Display a substring:

Task
Substring
You are encouraged to solve this task according to the task description, using any language you may know.

Basic Data Operation
This is a basic data operation. It represents a fundamental action on a basic data type.

You may see other such operations in the Basic Data Operations category, or:

Integer Operations
Arithmetic | Comparison

Boolean Operations
Bitwise | Logical

String Operations
Concatenation | Interpolation | Comparison | Matching

Memory Operations
Pointers & references | Addresses


Task
  •   starting from   n   characters in and of   m   length;
  •   starting from   n   characters in,   up to the end of the string;
  •   whole string minus the last character;
  •   starting from a known   character   within the string and of   m   length;
  •   starting from a known   substring   within the string and of   m   length.


If the program uses UTF-8 or UTF-16,   it must work on any valid Unicode code point, whether in the   Basic Multilingual Plane   or above it.

The program must reference logical characters (code points),   not 8-bit code units for UTF-8 or 16-bit code units for UTF-16.

Programs for other encodings (such as 8-bit ASCII, or EUC-JP) are not required to handle all Unicode characters.


Other tasks related to string operations:
Metrics
Counting
Remove/replace
Anagrams/Derangements/shuffling
Find/Search/Determine
Formatting
Song lyrics/poems/Mad Libs/phrases
Tokenize
Sequences



11l

Translation of: Python
V s = ‘abcdefgh’
V n = 2
V m = 3
V char = ‘d’
V chars = ‘cd’
print(s[n - 1 .+ m])          // starting from n=2 characters in and m=3 in length
print(s[n - 1 ..])            // starting from n characters in, up to the end of the string
print(s[0 .< (len)-1])        // whole string minus last character
print(s[s.index(char) .+ m])  // starting from a known character char="d" within the string and of m length
print(s[s.index(chars) .+ m]) // starting from a known substring chars="cd" within the string and of m length
Output:
bcd
bcdefgh
abcdefg
def
cde

AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits
/* ARM assembly AARCH64 Raspberry PI 3B */
/*  program subString64.s   */
 
/*******************************************/
/* Constantes file                         */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"

/*******************************************/
/* Initialized data                        */
/*******************************************/
.data
szMessString:            .asciz "Result : " 
szString1:               .asciz "abcdefghijklmnopqrstuvwxyz"
szStringStart:           .asciz "abcdefg"
szCarriageReturn:        .asciz "\n"
/*******************************************/ 
/* UnInitialized data                      */
/*******************************************/
.bss 
szSubString:             .skip 500             // buffer result
 
/*******************************************/
/*  code section                           */
/*******************************************/
.text
.global main 
main: 
 
    ldr x0,qAdrszString1                        // address input string
    ldr x1,qAdrszSubString                      // address output string
    mov x2,22                                   // location
    mov x3,4                                    // length
    bl subStringNbChar                          // starting from n characters in and of m length
    ldr x0,qAdrszMessString                     // display message
    bl affichageMess
    ldr x0,qAdrszSubString                      // display substring result
    bl affichageMess
    ldr x0,qAdrszCarriageReturn                 // display line return
    bl affichageMess
    //
    ldr x0,qAdrszString1
    ldr x1,qAdrszSubString
    mov x2,15                                   // location
    bl subStringEnd                             //starting from n characters in, up to the end of the string
    ldr x0,qAdrszMessString                     // display message
    bl affichageMess
    ldr x0,qAdrszSubString
    bl affichageMess
    ldr x0,qAdrszCarriageReturn                 // display line return
    bl affichageMess
    //
    ldr x0,qAdrszString1
    ldr x1,qAdrszSubString
    bl subStringMinus                           // whole string minus last character
    ldr x0,qAdrszMessString                     // display message
    bl affichageMess
    ldr x0,qAdrszSubString
    bl affichageMess
    ldr x0,qAdrszCarriageReturn                 // display line return
    bl affichageMess
    //
    ldr x0,qAdrszString1
    ldr x1,qAdrszSubString
    mov x2,'c'                                  // start character
    mov x3,5                                    // length
    bl subStringStChar                          //starting from a known character within the string and of m length
    cmp x0,-1                                   // error ?
    beq 2f
    ldr x0,qAdrszMessString                     // display message
    bl affichageMess
    ldr x0,qAdrszSubString
    bl affichageMess
    ldr x0,qAdrszCarriageReturn                 // display line return
    bl affichageMess
    //
2:
    ldr x0,qAdrszString1
    ldr x1,qAdrszSubString
    ldr x2,qAdrszStringStart                    // sub string to start
    mov x3,10                                   // length
    bl subStringStString                        // starting from a known substring within the string and of m length
    cmp x0,-1                                   // error ?
    beq 3f
    ldr x0,qAdrszMessString                     // display message
    bl affichageMess
    ldr x0,qAdrszSubString
    bl affichageMess
    ldr x0,qAdrszCarriageReturn                 // display line return
    bl affichageMess
3:
100:                                            // standard end of the program
    mov x0,0                                    // return code
    mov x8,EXIT                                 // request to exit program
    svc 0                                       // perform system call
qAdrszMessString:         .quad szMessString
qAdrszString1:            .quad szString1
qAdrszSubString:          .quad szSubString
qAdrszStringStart:        .quad szStringStart
qAdrszCarriageReturn:     .quad szCarriageReturn
/******************************************************************/
/*     sub strings  index start  number of characters             */ 
/******************************************************************/
/* x0 contains the address of the input string */
/* x1 contains the address of the output string */
/* x2 contains the start index                  */
/* x3 contains numbers of characters to extract */
/* x0 returns number of characters or -1 if error */
subStringNbChar:
    stp x1,lr,[sp,-16]!            // save  registers
    mov x14,#0                     // counter byte output string 
1:
    ldrb w15,[x0,x2]               // load byte string input
    cbz x15,2f                     // zero final ?
    strb w15,[x1,x14]              // store byte output string
    add x2,x2,1                    // increment counter
    add x14,x14,1
    cmp x14,x3                     // end ?
    blt 1b                         // no -> loop
2:
    strb wzr,[x1,x14]              // store final zero byte string 2
    mov x0,x14
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/******************************************************************/
/*     sub strings  index start at end of string             */ 
/******************************************************************/
/* x0 contains the address of the input string */
/* x1 contains the address of the output string */
/* x2 contains the start index                  */
/* x0 returns number of characters or -1 if error */
subStringEnd:
    stp x2,lr,[sp,-16]!            // save  registers
    mov x14,0                      // counter byte output string 
1:
    ldrb w15,[x0,x2]               // load byte string 1
    cbz x15,2f                     // zero final ?
    strb w15,[x1,x14]
    add x2,x2,1
    add x14,x14,1
    b 1b                           // loop
2:
    strb wzr,[x1,x14]              // store final zero byte string 2
    mov x0,x14
100:

    ldp x2,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/******************************************************************/
/*      whole string minus last character                        */ 
/******************************************************************/
/* x0 contains the address of the input string */
/* x1 contains the address of the output string */
/* x0 returns number of characters or -1 if error */
subStringMinus:
    stp x1,lr,[sp,-16]!            // save  registers
    mov x12,0                      // counter byte input string
    mov x14,0                      // counter byte output string 
1:
    ldrb w15,[x0,x12]              // load byte string 
    cbz x15,2f                     // zero final ?
    strb w15,[x1,x14]
    add x12,x12,1
    add x14,x14,1
    b 1b                           //  loop
2:
    sub x14,x14,1
    strb wzr,[x1,x14]              // store final zero byte string 2
    mov x0,x14
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/******************************************************************/
/*   starting from a known character within the string and of m length  */ 
/******************************************************************/
/* x0 contains the address of the input string */
/* x1 contains the address of the output string */
/* x2 contains the character    */
/* x3 contains the length
/* x0 returns number of characters or -1 if error */
subStringStChar:
    stp x1,lr,[sp,-16]!            // save  registers
    mov x16,0                      // counter byte input string
    mov x14,0                      // counter byte output string 
1:
    ldrb w15,[x0,x16]              // load byte string 
    cbz x15,4f                     // zero final ?
    cmp x15,x2                     // character find ?
    beq 2f                         // yes
    add x16,x16,1                  // no -> increment indice
    b 1b                           //  loop
2:
    strb w15,[x1,x14]
    add x16,x16,1
    add x14,x14,1
    cmp x14,x3
    bge 3f
    ldrb w15,[x0,x16]              // load byte string 
    cbnz x15,2b                    // loop if no zero final
3:
    strb wzr,[x1,x14]              // store final zero byte string 2
    mov x0,x14
    b 100f
4:
    strb w15,[x1,x14]
    mov x0,#-1
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/******************************************************************/
/*   starting from a known substring within the string and of m length  */ 
/******************************************************************/
/* x0 contains the address of the input string */
/* x1 contains the address of the output string */
/* x2 contains the address of string to start    */
/* x3 contains the length
/* x0 returns number of characters or -1 if error */
subStringStString:
    stp x1,lr,[sp,-16]!            // save  registers
    stp x20,x21,[sp,-16]!          // save  registers
    mov x20,x0                     // save address
    mov x21,x1                     // save address output string
    mov x1,x2
    bl searchSubString
    cmp x0,-1                      // not found ?
    beq 100f
    mov x16,x0                     // counter byte input string
    mov x14,0
1:
    ldrb w15,[x20,x16]             // load byte string 
    strb w15,[x21,x14]
    cmp x15,#0                     // zero final ?
    csel x0,x14,x0,eq
    beq 100f
    add x14,x14,1
    cmp x14,x3
    add x15,x16,1
    csel x16,x15,x16,lt
    blt 1b                         //  loop
    strb wzr,[x21,x14]
    mov x0,x14                     // return indice
100:
    ldp x20,x21,[sp],16              // restaur  2 registers
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/******************************************************************/
/*   search a substring in the string                            */ 
/******************************************************************/
/* x0 contains the address of the input string */
/* x1 contains the address of substring */
/* x0 returns index of substring in string or -1 if not found */
searchSubString:
    stp x1,lr,[sp,-16]!            // save  registers
    mov x12,0                      // counter byte input string
    mov x13,0                      // counter byte string 
    mov x16,-1                     // index found
    ldrb w14,[x1,x13]
1:
    ldrb w15,[x0,x12]              // load byte string 
    cbz x15,4f                     // zero final ?
    cmp x15,x14                    // compare character 
    beq 2f
    mov x16,-1                     // no equals - > raz index 
    mov x13,0                      // and raz counter byte
    add x12,x12,1                  // and increment counter byte
    b 1b                           // and loop
2:                                 // characters equals
    cmp x16,-1                     // first characters equals ?
    csel x16,x12,x16,eq
   // moveq x6,x2                  // yes -> index begin in x6
    add x13,x13,1                  // increment counter substring
    ldrb w14,[x1,x13]              // and load next byte
    cbz x14,3f                     // zero final ? yes -> end search
    add x12,x12,1                  // else increment counter string
    b 1b                           // and loop
3:
    mov x0,x16                     // return indice
    b 100f
4:
   mov x0,#-1                      // yes returns error
100:
    ldp x1,lr,[sp],16              // restaur  2 registers
    ret                            // return to address lr x30
/********************************************************/
/*        File Include fonctions                        */
/********************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"
Output:
Result : wxyz
Result : pqrstuvwxyz
Result : abcdefghijklmnopqrstuvwxy
Result : cdefg
Result : abcdefghij

Action!

BYTE FUNC FindC(CHAR ARRAY text CHAR c)
  BYTE i

  i=1
  WHILE i<=text(0)
  DO
    IF text(i)=c THEN
      RETURN (i)
    FI
    i==+1
  OD
RETURN (0)

BYTE FUNC FindS(CHAR ARRAY text,sub)
  BYTE i,j,found

  i=1
  WHILE i<=text(0)-sub(0)+1
  DO
    found=0
    FOR j=1 TO sub(0)
    DO
      IF text(i+j-1)#sub(j) THEN
        found=0 EXIT
      ELSE
        found=1
      FI
    OD
    IF found THEN
      RETURN (i)
    FI
    i==+1
  OD
RETURN (0)

PROC Main()
  CHAR ARRAY text="qwertyuiop"
  CHAR ARRAY sub="tyu"
  CHAR ARRAY res(20)
  BYTE n,m
  CHAR c

  PrintF("Original string:%E  ""%S""%E%E",text)

  n=3 m=5
  SCopyS(res,text,n,n+m-1)
  PrintF("Substring start from %B and length %B:%E  ""%S""%E%E",n,m,res)

  n=4
  SCopyS(res,text,n,text(0))
  PrintF("Substring start from %B up to the end:%E  ""%S""%E%E",n,res)

  SCopyS(res,text,1,text(0)-1)
  PrintF("Whole string without the last char:%E  ""%S""%E%E",res)

  c='w m=4
  n=FindC(text,c)
  IF n=0 THEN
    PrintF("Character '%C' not found in string%E%E",c)
  ELSE
    SCopyS(res,text,n,n+m-1)
    PrintF("Substring start from '%C' and len %B:%E  ""%S""%E%E",c,m,res)
  FI

  n=FindS(text,sub)
  m=6
  IF n=0 THEN
    PrintF("String ""%S"" not found in string%E%E",sub)
  ELSE
    SCopyS(res,text,n,n+m-1)
    PrintF("Substring start from '%S' and len %B:  ""%S""%E%E",sub,m,res)
  FI
RETURN
Output:

Screenshot from Atari 8-bit computer

Original string:
  "qwertyuiop"

Substring start from 3 and length 5:
  "ertyu"

Substring start from 4 up to the end:
  "rtyuiop"

Whole string without the last char:
  "qwertyuio"

Substring start from 'w' and len 4:
  "wert"

Substring start from 'tyu' and len 6:
  "tyuiop"

Ada

String in Ada is an array of Character elements indexed by Positive:

type String is array (Positive range <>) of Character;

Substring is a first-class object in Ada, an anonymous subtype of String. The language uses the term slice for it. Slices can be retrieved, assigned and passed as a parameter to subprograms in mutable or immutable mode. A slice is specified as:

A (<first-index>..<last-index>)

A string array in Ada can start with any positive index. This is why the implementation below uses Str'First in all slices, which in this concrete case is 1, but intentionally left in the code because the task refers to N as an offset to the string beginning rather than an index in the string. In Ada it is unusual to deal with slices in such way. One uses plain string index instead.

with Ada.Text_IO;        use Ada.Text_IO;
with Ada.Strings.Fixed;  use Ada.Strings.Fixed;

procedure Test_Slices is
   Str : constant String := "abcdefgh";
   N : constant := 2;
   M : constant := 3;
begin
   Put_Line (Str (Str'First + N - 1..Str'First + N + M - 2));
   Put_Line (Str (Str'First + N - 1..Str'Last));
   Put_Line (Str (Str'First..Str'Last - 1));
   Put_Line (Head (Tail (Str, Str'Last - Index (Str, "d", 1)), M));
   Put_Line (Head (Tail (Str, Str'Last - Index (Str, "de", 1) - 1), M));
end Test_Slices;
Output:
bcd
bcdefgh
abcdefg
efg
fgh

Aikido

Aikido uses square brackets for slices. The syntax is [start:end]. If you want to use length you have to add to the start. Shifting strings left or right removes characters from the ends.

const str = "abcdefg"
var n = 2
var m = 3

println (str[n:n+m-1])    // pos 2 length 3
println (str[n:])           // pos 2 to end
println (str >> 1)      // remove last character
var p = find (str, 'c')
println (str[p:p+m-1])    // from pos of p length 3

var s = find (str, "bc")
println (str[s, s+m-1])    // pos of bc length 3

Aime

text s;
data b, d;

s = "The quick brown fox jumps over the lazy dog.";

o_text(cut(s, 4, 15));
o_newline();
o_text(cut(s, 4, length(s)));
o_newline();
o_text(delete(s, -1));
o_newline();
o_text(cut(s, index(s, 'q'), 5));
o_newline();

b_cast(b, s);
b_cast(d, "brown");
o_text(cut(s, b_find(b, d), 15));
o_newline();
Output:
quick brown fox
quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog
quick
brown fox jumps

ALGOL 68

Translation of: python
Works with: ALGOL 68 version Standard - no extensions to language used
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny
main: (
  STRING s = "abcdefgh";
  INT n = 2, m = 3; 
  CHAR char = "d"; 
  STRING chars = "cd";

  printf(($gl$, s[n:n+m-1]));
  printf(($gl$, s[n:]));
  printf(($gl$, s[:UPB s-1]));
 
  INT pos; 
  char in string("d", pos, s);
  printf(($gl$, s[pos:pos+m-1]));
  string in string("de", pos, s);
  printf(($gl$, s[pos:pos+m-1]))
)
Output:
bcd
bcdefgh
abcdefg
def
def

Apex

In Apex, the substring method returns a new String that begins with the character at the specified zero-based startIndex and extends to the end of the String.

String x = 'testing123';
//Test1: testing123
System.debug('Test1: ' + x.substring(0,x.length()));
//Test2: esting123
System.debug('Test2: ' + x.substring(1,x.length()));
//Test3: testing123
System.debug('Test3: ' + x.substring(0));
//Test4: 3
System.debug('Test4: ' + x.substring(x.length()-1));
//Test5: 
System.debug('Test5: ' + x.substring(1,1));
//Test 6: testing123
System.debug('Test6: ' + x.substring(x.indexOf('testing')));
//Test7: e
System.debug('Test7: ' + x.substring(1,2));

AppleScript

Expressed in terms of some familiar functional primitives, so that we can focus more on the task, without too much distraction by the parochial quirks of a particular scripting language.

Translation of: JavaScript

(Functional primitives version)

Translation of: Haskell
-- SUBSTRINGS -----------------------------------------------------------------

--  take :: Int -> Text -> Text
on take(n, s)
    text 1 thru n of s
end take

--  drop :: Int -> Text -> Text
on drop(n, s)
    text (n + 1) thru -1 of s
end drop

-- breakOn :: Text -> Text -> (Text, Text)
on breakOn(strPattern, s)
    set {dlm, my text item delimiters} to {my text item delimiters, strPattern}
    set lstParts to text items of s
    set my text item delimiters to dlm
    {item 1 of lstParts, strPattern & (item 2 of lstParts)}
end breakOn

--  init :: Text -> Text
on init(s)
    if length of s > 0 then
        text 1 thru -2 of s
    else
        missing value
    end if
end init


-- TEST -----------------------------------------------------------------------
on run
    set str to "一二三四五六七八九十"
    
    set legends to {¬
        "from n in, of n length", ¬
        "from n in, up to end", ¬
        "all but last", ¬
        "from matching char, of m length", ¬
        "from matching string, of m length"}
    
    set parts to {¬
        take(3, drop(4, str)), ¬
        drop(3, str), ¬
        init(str), ¬
        take(3, item 2 of breakOn("五", str)), ¬
        take(4, item 2 of breakOn("六七", str))}
    
    script tabulate
        property strPad : "                                        "
        
        on |λ|(l, r)
            l & drop(length of l, strPad) & r
        end |λ|
    end script
    
    linefeed & intercalate(linefeed, ¬
        zipWith(tabulate, ¬
            legends, parts)) & linefeed
end run

-- GENERIC FUNCTIONS FOR TEST -------------------------------------------------

-- intercalate :: Text -> [Text] -> Text
on intercalate(strText, lstText)
    set {dlm, my text item delimiters} to {my text item delimiters, strText}
    set strJoined to lstText as text
    set my text item delimiters to dlm
    return strJoined
end intercalate

-- min :: Ord a => a -> a -> a
on min(x, y)
    if y < x then
        y
    else
        x
    end if
end min

-- Lift 2nd class handler function into 1st class script wrapper 
-- mReturn :: Handler -> Script
on mReturn(f)
    if class of f is script then
        f
    else
        script
            property |λ| : f
        end script
    end if
end mReturn

-- zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
on zipWith(f, xs, ys)
    set lng to min(length of xs, length of ys)
    set lst to {}
    tell mReturn(f)
        repeat with i from 1 to lng
            set end of lst to |λ|(item i of xs, item i of ys)
        end repeat
        return lst
    end tell
end zipWith
Output:
from n in, of n length                  五六七
from n in, up to end                    四五六七八九十
all but last                            一二三四五六七八九
from matching char, of m length         五六七
from matching string, of m length       六七八九

ARM Assembly

Works with: as version Raspberry Pi
/* ARM assembly Raspberry PI  */
/*  program substring.s   */

/* Constantes    */
.equ STDOUT, 1                           @ Linux output console
.equ EXIT,   1                           @ Linux syscall
.equ WRITE,  4                           @ Linux syscall

.equ BUFFERSIZE,          100

/* Initialized data */
.data
szMessString:            .asciz "Result : " 
szString1:               .asciz "abcdefghijklmnopqrstuvwxyz"
szStringStart:           .asciz "abcdefg"
szCarriageReturn:        .asciz "\n"

/* UnInitialized data */
.bss 
szSubString:             .skip 500             @ buffer result


/*  code section */
.text
.global main 
main: 

    ldr r0,iAdrszString1                        @ address input string
    ldr r1,iAdrszSubString                      @ address output string
    mov r2,#22                                  @ location
    mov r3,#4                                   @ length
    bl subStringNbChar                          @ starting from n characters in and of m length
    ldr r0,iAdrszMessString                     @ display message
    bl affichageMess
    ldr r0,iAdrszSubString                      @ display substring result
    bl affichageMess
    ldr r0,iAdrszCarriageReturn                 @ display line return
    bl affichageMess
    @
    ldr r0,iAdrszString1
    ldr r1,iAdrszSubString
    mov r2,#15                                  @ location
    bl subStringEnd                             @starting from n characters in, up to the end of the string
    ldr r0,iAdrszMessString                     @ display message
    bl affichageMess
    ldr r0,iAdrszSubString
    bl affichageMess
    ldr r0,iAdrszCarriageReturn                 @ display line return
    bl affichageMess
    @
    ldr r0,iAdrszString1
    ldr r1,iAdrszSubString
    bl subStringMinus                           @ whole string minus last character
    ldr r0,iAdrszMessString                     @ display message
    bl affichageMess
    ldr r0,iAdrszSubString
    bl affichageMess
    ldr r0,iAdrszCarriageReturn                 @ display line return
    bl affichageMess
    @
    ldr r0,iAdrszString1
    ldr r1,iAdrszSubString
    mov r2,#'c'                                 @ start character
    mov r3,#5                                   @ length
    bl subStringStChar                          @starting from a known character within the string and of m length
    cmp r0,#-1                                  @ error ?
    beq 2f
    ldr r0,iAdrszMessString                     @ display message
    bl affichageMess
    ldr r0,iAdrszSubString
    bl affichageMess
    ldr r0,iAdrszCarriageReturn                 @ display line return
    bl affichageMess
    @
2:
    ldr r0,iAdrszString1
    ldr r1,iAdrszSubString
    ldr r2,iAdrszStringStart                    @ sub string to start
    mov r3,#10                                  @ length
    bl subStringStString                        @ starting from a known substring within the string and of m length
    cmp r0,#-1                                  @ error ?
    beq 3f
    ldr r0,iAdrszMessString                     @ display message
    bl affichageMess
    ldr r0,iAdrszSubString
    bl affichageMess
    ldr r0,iAdrszCarriageReturn                 @ display line return
    bl affichageMess
3:
100:                                            @ standard end of the program
    mov r0, #0                                  @ return code
    mov r7, #EXIT                               @ request to exit program
    svc 0                                       @ perform system call
iAdrszMessString:         .int szMessString
iAdrszString1:            .int szString1
iAdrszSubString:            .int szSubString
iAdrszStringStart:            .int szStringStart
iAdrszCarriageReturn:     .int szCarriageReturn
/******************************************************************/
/*     sub strings  index start  number of characters             */ 
/******************************************************************/
/* r0 contains the address of the input string */
/* r1 contains the address of the output string */
/* r2 contains the start index                  */
/* r3 contains numbers of characters to extract */
/* r0 returns number of characters or -1 if error */
subStringNbChar:
    push {r1-r5,lr}                             @ save  registers 
    mov r4,#0                                   @ counter byte output string 
1:
    ldrb r5,[r0,r2]                             @ load byte string input
    cmp r5,#0                                   @ zero final ?
    beq 2f
    strb r5,[r1,r4]                             @ store byte output string
    add r2,#1                                   @ increment counter
    add r4,#1
    cmp r4,r3                                   @ end ?
    blt 1b                                      @ no -> loop
2:
    mov r5,#0
    strb r5,[r1,r4]                             @ load byte string 2
    mov r0,r4
100:
    pop {r1-r5,lr}                              @ restaur registers
    bx lr                                       @ return
/******************************************************************/
/*     sub strings  index start at end of string             */ 
/******************************************************************/
/* r0 contains the address of the input string */
/* r1 contains the address of the output string */
/* r2 contains the start index                  */
/* r0 returns number of characters or -1 if error */
subStringEnd:
    push {r1-r5,lr}                             @ save registers 
    mov r4,#0                                   @ counter byte output string 
1:
    ldrb r5,[r0,r2]                             @ load byte string 1
    cmp r5,#0                                   @ zero final ?
    beq 2f
    strb r5,[r1,r4]
    add r2,#1
    add r4,#1
    b 1b                                        @ loop
2:
    mov r5,#0
    strb r5,[r1,r4]                             @ load byte string 2
    mov r0,r4
100:
    pop {r1-r5,lr}                              @ restaur registers
    bx lr   
/******************************************************************/
/*      whole string minus last character                        */ 
/******************************************************************/
/* r0 contains the address of the input string */
/* r1 contains the address of the output string */
/* r0 returns number of characters or -1 if error */
subStringMinus:
    push {r1-r5,lr}                             @ save  registers 
    mov r2,#0                                   @ counter byte input string
    mov r4,#0                                   @ counter byte output string 
1:
    ldrb r5,[r0,r2]                             @ load byte string 
    cmp r5,#0                                   @ zero final ?
    beq 2f
    strb r5,[r1,r4]
    add r2,#1
    add r4,#1
    b 1b                                        @  loop
2:
    sub r4,#1
    mov r5,#0
    strb r5,[r1,r4]                             @ load byte string 2
    mov r0,r4
100:
    pop {r1-r5,lr}                              @ restaur registers
    bx lr   
/******************************************************************/
/*   starting from a known character within the string and of m length  */ 
/******************************************************************/
/* r0 contains the address of the input string */
/* r1 contains the address of the output string */
/* r2 contains the character    */
/* r3 contains the length
/* r0 returns number of characters or -1 if error */
subStringStChar:
    push {r1-r5,lr}                             @ save  registers 
    mov r6,#0                                   @ counter byte input string
    mov r4,#0                                   @ counter byte output string 

1:
    ldrb r5,[r0,r6]                             @ load byte string 
    cmp r5,#0                                   @ zero final ?
    streqb r5,[r1,r4]
    moveq r0,#-1
    beq 100f
    cmp r5,r2
    beq 2f
    add r6,#1
    b 1b                                        @  loop
2:
    strb r5,[r1,r4]
    add r6,#1
    add r4,#1
    cmp r4,r3
    bge 3f
    ldrb r5,[r0,r6]                             @ load byte string 
    cmp r5,#0
    bne 2b
3:
    mov r5,#0
    strb r5,[r1,r4]                             @ load byte string 2
    mov r0,r4
100:
    pop {r1-r5,lr}                              @ restaur registers
    bx lr   

/******************************************************************/
/*   starting from a known substring within the string and of m length  */ 
/******************************************************************/
/* r0 contains the address of the input string */
/* r1 contains the address of the output string */
/* r2 contains the address of string to start    */
/* r3 contains the length
/* r0 returns number of characters or -1 if error */
subStringStString:
    push {r1-r8,lr}                             @ save  registers 
    mov r7,r0                                   @ save address
    mov r8,r1                                   @ counter byte string 
    mov r1,r2
    bl searchSubString
    cmp r0,#-1
    beq 100f
    mov r6,r0                                   @ counter byte input string
    mov r4,#0
1:
    ldrb r5,[r7,r6]                             @ load byte string 
    strb r5,[r8,r4]
    cmp r5,#0                                   @ zero final ?
    moveq r0,r4
    beq 100f
    add r4,#1
    cmp r4,r3
    addlt r6,#1
    blt 1b                                      @  loop
    mov r5,#0
    strb r5,[r8,r4]
    mov r0,r4
100:
    pop {r1-r8,lr}                              @ restaur registers
    bx lr   

/******************************************************************/
/*   search a substring in the string                            */ 
/******************************************************************/
/* r0 contains the address of the input string */
/* r1 contains the address of substring */
/* r0 returns index of substring in string or -1 if not found */
searchSubString:
    push {r1-r6,lr}                       @ save registers 
    mov r2,#0                             @ counter byte input string
    mov r3,#0                             @ counter byte string 
    mov r6,#-1                            @ index found
    ldrb r4,[r1,r3]
1:
    ldrb r5,[r0,r2]                       @ load byte string 
    cmp r5,#0                             @ zero final ?
    moveq r0,#-1                          @ yes returns error
    beq 100f
    cmp r5,r4                             @ compare character 
    beq 2f
    mov r6,#-1                            @ no equals - > raz index 
    mov r3,#0                             @ and raz counter byte
    add r2,#1                             @ and increment counter byte
    b 1b                                  @ and loop
2:                                        @ characters equals
    cmp r6,#-1                            @ first characters equals ?
    moveq r6,r2                           @ yes -> index begin in r6
    add r3,#1                             @ increment counter substring
    ldrb r4,[r1,r3]                       @ and load next byte
    cmp r4,#0                             @ zero final ?
    beq 3f                                @ yes -> end search
    add r2,#1                             @ else increment counter string
    b 1b                                  @ and loop
3:
    mov r0,r6
100:
    pop {r1-r6,lr}                        @ restaur registers
    bx lr   

/******************************************************************/
/*     display text with size calculation                         */ 
/******************************************************************/
/* r0 contains the address of the message */
affichageMess:
    push {r0,r1,r2,r7,lr}                       @ save  registers 
    mov r2,#0                                   @ counter length */
1:                                              @ loop length calculation
    ldrb r1,[r0,r2]                             @ read octet start position + index 
    cmp r1,#0                                   @ if 0 its over
    addne r2,r2,#1                              @ else add 1 in the length
    bne 1b                                      @ and loop 
                                                @ so here r2 contains the length of the message 
    mov r1,r0                                   @ address message in r1 
    mov r0,#STDOUT                              @ code to write to the standard output Linux
    mov r7, #WRITE                              @ code call system "write" 
    svc #0                                      @ call system
    pop {r0,r1,r2,r7,lr}                        @ restaur registers
    bx lr                                       @ return

Arturo

str: "abcdefgh"
n: 2
m: 3

; starting from n=2 characters in and m=3 in length
print slice str n-1 n+m-2

; starting from n characters in, up to the end of the string
print slice str n-1 (size str)-1

; whole string minus last character
print slice str 0 (size str)-2

; starting from a known character char="d" 
; within the string and of m length
print slice str index str "d" m+(index str "d")-1

; starting from a known substring chars="cd" 
; within the string and of m length
print slice str index str "cd" m+(index str "cd")-1
Output:
bcd
bcdefgh
abcdefg
def
cde

AutoHotkey

The code contains some alternatives.

String := "abcdefghijklmnopqrstuvwxyz"
; also: String = abcdefghijklmnopqrstuvwxyz
n := 12
m := 5

; starting from n characters in and of m length;
subString := SubStr(String, n, m)
; alternative:  StringMid, subString, String, n, m
MsgBox % subString

; starting from n characters in, up to the end of the string;
subString := SubStr(String, n)
; alternative:  StringMid, subString, String, n
MsgBox % subString

; whole string minus last character;
StringTrimRight, subString, String, 1
; alternatives: subString := SubStr(String, 1, StrLen(String) - 1)
;               StringMid, subString, String, 1, StrLen(String) - 1
MsgBox % subString

; starting from a known character within the string and of m length;
findChar := "q"
subString := SubStr(String, InStr(String, findChar), m)
; alternatives: RegExMatch(String, findChar . ".{" . m - 1 . "}", subString)
;               StringMid, subString, String, InStr(String, findChar), m
MsgBox % subString

; starting from a known character within the string and of m length;
findString := "pq"
subString := SubStr(String, InStr(String, findString), m)
; alternatives: RegExMatch(String, findString . ".{" . m - StrLen(findString) . "}", subString)
;               StringMid, subString, String, InStr(String, findString), m
MsgBox % subString
Output:
 lmnop
 lmnopqrstuvwxyz
 abcdefghijklmnopqrstuvwxy
 qrstu
 pqrst

AWK

Translation of: AutoHotKey
BEGIN {
	str = "abcdefghijklmnopqrstuvwxyz"
	n = 12
	m = 5

	print substr(str, n, m)
	print substr(str, n)
	print substr(str, 1, length(str) - 1)
	print substr(str, index(str, "q"), m)
	print substr(str, index(str, "pq"), m)
}
Output:
$ awk -f substring.awk  
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
qrstu
pqrst

Axe

This example is in need of improvement:

Add an example for substring start index.

Lbl SUB1
0→{r₁+r₂+r₃}
r₁+r₂
Return

Lbl SUB2
r₁+r₂
Return

Lbl SUB3
0→{r₁+length(r₁)-1}
r₁
Return

Lbl SUB4
inData(r₂,r₁)-1→I
0→{r₁+I+r₃}
r₁+I
Return

BASIC

Applesoft BASIC

0 READ N, M, S$ : L = LEN(S$) : GOSUB 1 : END : DATA 5,11,THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG,J,FOX

REM          starting from   n   characters in and of   m   length;
1 PRINT MID$(S$,N,M)

REM          starting from   n   characters in,   up to the end of the string;
2 PRINT RIGHT$(S$,L-N+1)

REM          whole string minus the last character;
3 PRINT LEFT$(S$,L-1)

REM          starting from a known   character   within the string and of   m   length;
4 READ F$ :GOSUB 6

REM          starting from a known   substring   within the string and of   m   length.
5 READ F$

6 FOR I = 1 TO L : IF MID$(S$,I,LEN(F$)) = F$ THEN PRINT MID$(S$,I,M) : RETURN
7 NEXT : RETURN

ASIC

REM Substring
Base$ = "abcdefghijklmnopqrstuvwxyz"
N = 12
M = 5

REM Starting from N characters in and of M length.
Sub$ = MID$(Base$, N, M)
PRINT Sub$

REM Starting from N characters in, up to the end of the string.
L = LEN(Base$)
L = L - N 
L = L + 1
Sub$ = MID$(Base$, N, L)
PRINT Sub$

REM Whole string minus last character.
L = LEN(Base$)
L = L - 1
Sub$ = LEFT$(Base$, L)
PRINT Sub$

REM Starting from a known character within the string and of M length.
B = INSTR(Base$, "b")
Sub$ = MID$(Base$, B, M)
PRINT Sub$

REM Starting from a known substring within the string and of M length.
Find$ = "pq"
B = INSTR(Base$, Find$)
Sub$ = MID$(Base$, B, M)
PRINT Sub$
END
Output:
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
bcdef
pqrst

BASIC256

c$ = "abcdefghijklmnopqrstuvwxyz"
n = 12
m = 5
# starting from n characters in and of m length;
print mid(c$, n, m)
# starting from n characters in, up to the end of the string;
print mid(c$, n, length(c$))
# whole string minus last character;
print left(c$, length(c$) - 1)
# starting from a known character within the string and of m length;
print mid(c$, instr(c$, "b"), m)
# starting from a known substring within the string and of m length.
f$ = "pq"
print mid(c$, instr(c$, f$), m)
end
Output:
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
bcdef
pqrst

BBC BASIC

      basestring$ = "The five boxing wizards jump quickly"
      n% = 10
      m% = 5
      
      REM starting from n characters in and of m length:
      substring$ = MID$(basestring$, n%, m%)
      PRINT substring$
      
      REM starting from n characters in, up to the end of the string:
      substring$ = MID$(basestring$, n%)
      PRINT substring$
      
      REM whole string minus last character:
      substring$ = LEFT$(basestring$)
      PRINT substring$
      
      REM starting from a known character within the string and of m length:
      char$ = "w"
      substring$ = MID$(basestring$, INSTR(basestring$, char$), m%)
      PRINT substring$
      
      REM starting from a known substring within the string and of m length:
      find$ = "iz"
      substring$ = MID$(basestring$, INSTR(basestring$, find$), m%)
      PRINT substring$
Output:
boxin
boxing wizards jump quickly
The five boxing wizards jump quickl
wizar
izard

Commodore BASIC

10 REM SUBSTRING ... ROSETTACODE.ORG
20 A$ = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG"
30 X$ = "J" : S$ = "FOX"
40 N = 5: M = 11
50 PRINT "THE STRING:"
60 PRINT A$
70 PRINT
80 PRINT "SUBSTRING STARTING FROM" N "CHARACTERS IN AND OF" M "LENGTH:"
90 PRINT MID$(A$,N,M)
100 PRINT
110 PRINT "STARTING FROM" N "CHARACTERS IN, UP TO THE END OF THE STRING:"
120 PRINT RIGHT$(A$,LEN(A$)+1-N)
130 PRINT
140 PRINT "WHOLE STRING MINUS LAST CHARACTER:"
150 PRINT LEFT$(A$,LEN(A$)-1)
160 PRINT
170 PRINT "STARTING FROM '";X$;"' AND OF" M "LENGTH:"
180 I = 1
190 IF MID$(A$,I,1)=X$ THEN 220
200 I = I+1
210 GOTO 190
220 PRINT RIGHT$(A$,LEN(A$)+1-I)
230 PRINT
240 PRINT "STARTING FROM '";S$;"' AND OF" M "LENGTH:"
250 I = 1
260 IF MID$(A$,I,LEN(S$))=S$ THEN 290
270 I = I+1
280 GOTO 260
290 PRINT RIGHT$(A$,LEN(A$)+1-I)
300 END
Output:
THE STRING:
THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG

SUBSTRING STARTING FROM 5 CHARACTERS IN AND OF 11 LENGTH:
QUICK BROWN

STARTING FROM 5 CHARACTERS IN, UP TO THE END OF THE STRING:
QUICK BROWN FOX JUMPS OVER THE LAZY DOG

WHOLE STRING MINUS LAST CHARACTER:
THE QUICK BROWN FOX JUMPS OVER THE LAZY DO

STARTING FROM 'J' AND OF 11 LENGTH:
JUMPS OVER THE LAZY DOG

STARTING FROM 'FOX' AND OF 11 LENGTH:
FOX JUMPS OVER THE LAZY DOG

FreeBASIC

' FB 1.05.0 Win64

Dim s As String = "123456789"
Dim As Integer n = 3, m = 4
Print Mid(s, n, m)
Print Mid(s, n)
Print Left(s, Len(s) - 1)
'start from "5" say
Print Mid(s, Instr(s, "5"), m)
' start from "12" say
Print Mid(s, Instr(s, "12"), m)
Sleep
Output:
3456
3456789
12345678
5678
1234

FutureBasic

include "NSLog.incl"

void local fn DoIt
  CFStringRef string = @"abcdefghijklmnopqrstuvwxyz"
  
  NSLog(@"%@",mid(string,3,6))
  
  NSLog(@"%@",fn StringSubstringFromIndex( string, 10 ))
  
  NSLog(@"%@",left(string,len(string)-1))
  
  CFRange range = fn StringRangeOfString( string, @"r" )
  NSLog(@"%@",mid(string,range.location,6))
  
  range = fn StringRangeOfString( string, @"pqr" )
  NSLog(@"%@",mid(string,range.location,7))
end fn

fn DoIt

HandleEvents
Output:
defghi
klmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
rstuvw
pqrstuv

Gambas

Click this link to run this code

Public Sub Main()
Dim sString As String = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG"

Print Mid(sString, 11, 5)                     'Starting from n characters in and of m length
Print Mid(sString, 17)                        'Starting from n characters in, up to the end of the string
Print Left(sString, -1)                       'Whole string minus last character
Print Mid(sString, InStr(sString, "B"), 9)    'Starting from a known character within the string and of m length
Print Mid(sString, InStr(sString, "OVER"), 8) 'Starting from a known substring within the string and of m length

End

Output:

BROWN
FOX JUMPS OVER THE LAZY DOG
THE QUICK BROWN FOX JUMPS OVER THE LAZY DO
BROWN FOX
OVER THE

IS-BASIC

100 LET A$="abcdefghijklmnopqrstuvwxyz"
110 LET N=10:LET M=7
120 PRINT A$(N:N+M-1)
130 PRINT A$(N:)
140 PRINT A$(:LEN(A$)-1)
150 LET I=POS(A$,"g")
160 PRINT A$(I:I+M-1)
170 LET I=POS(A$,"ijk")
180 PRINT A$(I:I+M-1)

Liberty BASIC

'These tasks can be completed with various combinations of Liberty Basic's
'built in Mid$()/ Instr()/ Left$()/ Right$()/ and Len() functions, but these
'examples only use the Mid$()/ Instr()/ and Len() functions.

baseString$ = "Thequickbrownfoxjumpsoverthelazydog."
n = 12
m = 5

'starting from n characters in and of m length
Print Mid$(baseString$, n, m)

'starting from n characters in, up to the end of the string
Print Mid$(baseString$, n)

'whole string minus last character
Print Mid$(baseString$, 1, (Len(baseString$) - 1))

'starting from a known character within the string and of m length
Print Mid$(baseString$, Instr(baseString$, "f", 1), m)

'starting from a known substring within the string and of m length
Print Mid$(baseString$, Instr(baseString$, "jump", 1), m)

Nascom BASIC

Works with: Nascom ROM BASIC version 4.7
10 REM Substring
20 BAS$="abcdefghijklmnopqrstuvwxyz"
30 N=12:M=5
40 REM Starting from N characters in  
50 REM and of M length
60 SB$=MID$(BAS$,N,M)
70 PRINT SB$
80 REM Starting from N characters in, 
90 REM up to the end of the string
100 SB$=MID$(BAS$,N,LEN(BAS$)-N+1)
110 PRINT SB$
120 REM Whole string minus last character
130 SB$=LEFT$(BAS$,LEN(BAS$)-1)
140 PRINT SB$
150 REM Starting from a known character 
160 REM within the string and of M length
170 A$=BAS$:B$="b":GOSUB 270
180 SB$=MID$(BAS$,C,M)
190 PRINT SB$
200 REM Starting from a known substring 
210 REM within the string and of M length
220 A$=BAS$:B$="pq":GOSUB 270
230 SB$=MID$(BAS$,C,M)
240 PRINT SB$
250 END
260 REM ** INSTR subroutine
270 LB=LEN(B$):C=0 
280 FOR I=1 TO LEN(A$)-LB+1
290 IF MID$(A$,I,LB)=B$ THEN C=I:RETURN
300 NEXT I
310 RETURN
Output:
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
bcdef
pqrst

PureBasic

If OpenConsole()

  Define baseString.s, m, n
 
  baseString = "Thequickbrownfoxjumpsoverthelazydog."
  n = 12
  m = 5
 
  ;Display the substring starting from n characters in and of m length.
  PrintN(Mid(baseString, n, m))
 
  ;Display the substring starting from n characters in, up to the end of the string.
  PrintN(Mid(baseString, n)) ;or PrintN(Right(baseString, Len(baseString) - n))
 
  ;Display the substring whole string minus last character
  PrintN(Left(baseString, Len(baseString) - 1))
 
  ;Display the substring starting from a known character within the string and of m length.
  PrintN(Mid(baseString, FindString(baseString, "b", 1), m))

  ;Display the substring starting from a known substring within the string and of m length.
  PrintN(Mid(baseString, FindString(baseString, "ju", 1), m))

  Print(#CRLF$ + #CRLF$ + "Press ENTER to exit")
  Input()
  CloseConsole()
EndIf
Output:
wnfox
wnfoxjumpsoverthelazydog.
Thequickbrownfoxjumpsoverthelazydog
brown
jumps

QB64

DefStr S
DefInt I
string1 = "abcdefghijklmnopqrstuvwxyz"
substring = "klm"
Dim Achar As String * 1
Istart = 6
Ilength = 10
Achar = "c"

'  starting from   n   characters in and of   m   length;
Print Mid$(string1, Istart, Ilength)
'  starting from   n   characters in,   up to the end of the string;
Print Mid$(string1, Istart)
Print Right$(string1, Len(string1) - Istart + 1)
'  whole string minus the last character;
Print Left$(string1, Len(string1) - 1)
Print Mid$(string1, 1, Len(string1) - 1)
'  starting from a known   character   within the string and of   m   length;
Print Mid$(string1, InStr(string1, Achar), Ilength)
'  starting from a known   substring   within the string and of   m   length.
Print Mid$(string1, InStr(string1, substring), Ilength)
End

QuickBASIC

Works with: QBasic
DIM baseString AS STRING, subString AS STRING, findString AS STRING
DIM m AS INTEGER, n AS INTEGER

baseString = "abcdefghijklmnopqrstuvwxyz"
n = 12
m = 5

' starting from n characters in and of m length;
subString = MID$(baseString, n, m)
PRINT subString

' starting from n characters in, up to the end of the string;
subString = MID$(baseString, n)
PRINT subString

' whole string minus last character;
subString = LEFT$(baseString, LEN(baseString) - 1)
PRINT subString

' starting from a known character within the string and of m length;
subString = MID$(baseString, INSTR(baseString, "b"), m)
PRINT subString

' starting from a known substring within the string and of m length.
findString = "pq"
subString = MID$(baseString, INSTR(baseString, findString), m)
PRINT subString
Output:
 lmnop
 lmnopqrstuvwxyz
 abcdefghijklmnopqrstuvwxy
 bcdef
 pqrst

Run BASIC

n  = 2
m  = 3
s$ = "abcd"
a$ = mid$(a$,n,m)                  ' starting from n characters in and of m length
a$ = mid$(a$,n)                    ' starting from n characters in, up to the end of the string
a$ = Print mid$(a$,1,(len(a$)-1))  ' whole string minus last character
a$ = mid$(a$,instr(a$,s$,1),m)     ' starting from a known character within the string and of m length
a$ = mid$(a$,instr(a$,s$,1), m)    ' starting from a known substring within the string and of m length.

True BASIC

LET basestring$ = "abcdefghijklmnopqrstuvwxyz"
LET n = 12
LET m = 5
! starting from n characters in and of m length;
PRINT (basestring$)[n:n + m - 1]
! starting from n characters in, up to the end of the string;
PRINT (basestring$)[n:MAXNUM]
! whole string minus last character;
PRINT (basestring$)[1:LEN(basestring$) - 1]
! starting from a known character within the string and of m length;
PRINT (basestring$)[POS(basestring$,"b"):POS(basestring$,"b") + m - 1]
! starting from a known subString$ within the string and of m length.
LET findstring$ = "pq"
PRINT (basestring$)[POS(basestring$,findstring$):POS(basestring$,findstring$) + m - 1]
END

VBA

Translation of: Phix
Public Sub substring()
'(1) starting from n characters in and of m length;
'(2) starting from n characters in, up to the end of the string;
'(3) whole string minus last character;
'(4) starting from a known character within the string and of m length;
'(5) starting from a known substring within the string and of m length.
 
    sentence = "the last thing the man said was the"
    n = 10: m = 5
       
    '(1)
    Debug.Print Mid(sentence, n, 5)
    '(2)
    Debug.Print Right(sentence, Len(sentence) - n + 1)
    '(3)
    Debug.Print Left(sentence, Len(sentence) - 1)
    '(4)
    k = InStr(1, sentence, "m")
    Debug.Print Mid(sentence, k, 5)
    '(5)
    k = InStr(1, sentence, "aid")
    Debug.Print Mid(sentence, k, 5)
End Sub
Output:
thing
thing the man said was the
the last thing the man said was th
man s
aid w

VBScript

s = "rosettacode.org"

'starting from n characters in and of m length
WScript.StdOut.WriteLine Mid(s,8,4)

'starting from n characters in, up to the end of the string
WScript.StdOut.WriteLine Mid(s,8,Len(s)-7)

'whole string minus last character
WScript.StdOut.WriteLine Mid(s,1,Len(s)-1)

'starting from a known character within the string and of m length
WScript.StdOut.WriteLine Mid(s,InStr(1,s,"c"),4)

'starting from a known substring within the string and of m length
WScript.StdOut.WriteLine Mid(s,InStr(1,s,"ose"),6)
Output:
code
code.org
rosettacode.or
code
osetta

Yabasic

c$ = "abcdefghijklmnopqrstuvwxyz"
n = 12
m = 5
// starting from n characters in and of m length;
print mid$(c$, n, m)
// starting from n characters in, up to the end of the string;
print mid$(c$, n)
// whole string minus last character;
print left$(c$, len(c$) - 1)
// starting from a known character within the string and of m length;
print mid$(c$, instr(c$, "b"), m)
// starting from a known substring within the string and of m length.
f$ = "pq"
print mid$(c$, instr(c$, f$), m)
end
Output:
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
bcdef
pqrst

ZX Spectrum Basic

ZX Spectrum Basic has unfortunately no direct way to find a substring within a string, however a similar effect can be done searching with a for loop:

10 LET A$="abcdefghijklmnopqrstuvwxyz"
15 LET n=10: LET m=7
20 PRINT A$(n TO n+m-1)
30 PRINT A$(n TO )
40 PRINT A$( TO LEN (A$)-1)
50 FOR i=1 TO LEN (A$)
60 IF A$(i)="g" THEN PRINT A$(i TO i+m-1): LET i=LEN (A$): GO TO 70
70 NEXT i
80 LET B$="ijk"
90 FOR i=1 TO LEN (A$)-LEN (B$)+1
100 IF A$(i TO i+LEN (B$)-1)=B$ THEN PRINT A$(i TO i+m-1): LET i=LEN (A$)-LEN (B$)+1:  GO TO 110
110 NEXT i
120 STOP

Without superfluous code:

10 LET A$="abcdefghijklmnopqrstuvwxyz": LET la=LEN A$
20 LET n=10: LET m=7
30 PRINT A$(n TO n+m-1)
40 PRINT A$(n TO )
50 PRINT A$( TO la-1)
60 FOR i=1 TO la
70 IF A$(i)="g" THEN PRINT A$(i TO i+m-1): LET i=la
80 NEXT i
90 LET B$="ijk": LET lb=LEN b$
100 FOR i=1 TO la-lb+1
110 IF A$(i TO i+lb-1)=B$ THEN PRINT A$(i TO i+m-1): LET i=la-lb+1
120 NEXT i
Output:
jklmnop
jklmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
ghijklm
ijklmno

BQN

Similar to: J

(take) and (drop) are the main tools to use here. In CBQN these produce a slice type and thus take constant time regardless of the size of the argument or result.

   53"Marshmallow"
"shmal"
   3"Marshmallow"
"shmallow"
   ¯1"Marshmallow"
"Marshmallo"
   (/'m'=)"Marshmallow"
"mallow"
   (/"sh")"Marshmallow"
"shmallow"

Bracmat

Translation of: BBC BASIC
( (basestring = "The five boxing wizards jump quickly")
& (n = 10)
& (m = 5)

  { starting from n characters in and of m length: }
& @(!basestring:? [(!n+-1) ?substring [(!n+!m+-1) ?)
& out$!substring

  { starting from n characters in, up to the end of the string: }
& @(!basestring:? [(!n+-1) ?substring)
& out$!substring

  { whole string minus last character: }
& @(!basestring:?substring [-2 ?)
& out$!substring

  { starting from a known character within the string and of m length: }
& (char = "w")
& @(!basestring:? ([?p !char ?: ?substring [(!p+!m) ?))
& out$!substring

  { starting from a known substring within the string and of m length: }
& (find = "iz")
& @(!basestring:? ([?p !find ?: ?substring [(!p+!m) ?))
& out$!substring
&
)
Output:
boxin
boxing wizards jump quickly
The five boxing wizards jump quickl
wizar
izard

Burlesque

blsq ) "RosettaCode"5.+
"Roset"
blsq ) "RosettaCode"5.+2.-
"set"
blsq ) "RosettaCode""set"ss
2
blsq ) "RosettaCode"J"set"ss.-
"settaCode"
blsq ) "RosettaCode"~]
"RosettaCod"
blsq ) "RosettaCode"[-
"osettaCode"

Selecting/Deleting individual characters

blsq ) "RosettaCode"{0 1 3 5}si
"Roet"
blsq ) "RosettaCode"{0 1 3 5}di
"oetaCde"

C

C: ASCII version

/*
 * RosettaCode: Substring, C89
 *
 * In this task display a substring: starting from n characters in and of m
 * length; starting from n characters in, up to the end of the string; whole
 * string minus last character; starting from a known character within the
 * string and of m length; starting from a known substring within the string
 * and of m length.
 *
 * This example program DOES NOT make substrings. The program simply displays
 * certain parts of the input string.
 * 
 */
#define _CRT_SECURE_NO_WARNINGS /* MSVS compilers need this */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * Put no more than m characters from string to standard output.
 *
 * It is worth noting that printf("%*s",width,string) does not limit the number
 * of characters to be printed.
 *
 * @param string null terminated string
 * @param m      number of characters to display
 */
void putm(char* string, size_t m)
{
    while(*string && m--)
        putchar(*string++);
}

int main(void)
{

    char string[] = 
        "Programs for other encodings (such as 8-bit ASCII, or EUC-JP)."

    int n = 3;
    int m = 4;
    char knownCharacter = '(';
    char knownSubstring[] = "encodings";

    putm(string+n-1, m );                       putchar('\n');
    puts(string+n+1);                           putchar('\n');
    putm(string, strlen(string)-1);             putchar('\n');
    putm(strchr(string, knownCharacter), m );   putchar('\n');
    putm(strstr(string, knownSubstring), m );   putchar('\n');

    return EXIT_SUCCESS;
}

C: Unicode version

/*
 * RosettaCode: Substring, C89, Unicode
 *
 * In this task display a substring: starting from n characters in and of m
 * length; starting from n characters in, up to the end of the string; whole
 * string minus last character; starting from a known character within the
 * string and of m length; starting from a known substring within the string
 * and of m length.
 *
 * This example program DOES NOT make substrings. The program simply displays
 * certain parts of the input string.
 * 
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * Put all characters from string to standard output AND write newline.
 * BTW, _putws may not be avaliable.
 */
void put(wchar_t* string)
{
    while(*string)
        putwchar(*string++);
    putwchar(L'\n');
}

/*
 * Put no more than m characters from string to standard output AND newline.
 */
void putm(wchar_t* string, size_t m)
{
    while(*string && m--)
        putwchar(*string++);
    putwchar(L'\n');
}

int main(void)
{
    wchar_t string[] = 
        L"Programs for other encodings (such as 8-bit ASCII).";

    int n = 3;
    int m = 4;
    wchar_t knownCharacter = L'(';
    wchar_t knownSubstring[] = L"encodings";

    putm(string+n-1,m);                        
    put (string+n+1);                         
    putm(string, wcslen(string)-1);           
    putm(wcschr(string, knownCharacter), m ); 
    putm(wcsstr(string, knownSubstring), m ); 

    return EXIT_SUCCESS;
}

C: another version

#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char *substring(const char *s, size_t n, ptrdiff_t m)
{
  char *result;
  /* check for null s */
  if (NULL == s)
    return NULL;
  /* negative m to mean 'up to the mth char from right' */
  if (m < 0) 
    m = strlen(s) + m - n + 1;

  /* n < 0 or m < 0 is invalid */
  if (n < 0 || m < 0)
    return NULL;

  /* make sure string does not end before n 
   * and advance the "s" pointer to beginning of substring */
  for ( ; n > 0; s++, n--)
    if (*s == '\0')
      /* string ends before n: invalid */
      return NULL;

  result = malloc(m+1);
  if (NULL == result)
    /* memory allocation failed */
    return NULL;
  result[0]=0;
  strncat(result, s, m); /* strncat() will automatically add null terminator
                          * if string ends early or after reading m characters */
  return result;
}

char *str_wholeless1(const char *s)
{
  return substring(s, 0, strlen(s) - 1);
}

char *str_fromch(const char *s, int ch, ptrdiff_t m)
{
  return substring(s, strchr(s, ch) - s, m);
}

char *str_fromstr(const char *s, char *in, ptrdiff_t m)
{
  return substring(s, strstr(s, in) - s , m);
}


#define TEST(A) do {		\
    char *r = (A);		\
    if (NULL == r)		\
      puts("--error--");	\
    else {			\
      puts(r);			\
      free(r);			\
    }				\
  } while(0)

int main()
{
  const char *s = "hello world shortest program";

  TEST( substring(s, 12, 5) );		// get "short"
  TEST( substring(s, 6, -1) );		// get "world shortest program"
  TEST( str_wholeless1(s) );		// "... progra"
  TEST( str_fromch(s, 'w', 5) );	// "world"
  TEST( str_fromstr(s, "ro", 3) );	// "rog"

  return 0;
}

C++

#include <iostream>
#include <string>

int main()
{
  std::string s = "0123456789";

  int const n = 3;
  int const m = 4;
  char const c = '2';
  std::string const sub = "456";

  std::cout << s.substr(n, m)<< "\n";
  std::cout << s.substr(n) << "\n";
  std::cout << s.substr(0, s.size()-1) << "\n";
  std::cout << s.substr(s.find(c), m) << "\n";
  std::cout << s.substr(s.find(sub), m) << "\n";
}

C#

using System;
namespace SubString
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = "0123456789";
            const int n = 3;
            const int m = 2;
            const char c = '3';
            const string z = "345";

            // A: starting from n characters in and of m length;
            Console.WriteLine(s.Substring(n, m));
            // B: starting from n characters in, up to the end of the string;
            Console.WriteLine(s.Substring(n, s.Length - n));
            // C: whole string minus the last character;
            Console.WriteLine(s.Substring(0, s.Length - 1));
            // D: starting from a known character within the string and of m length;
            Console.WriteLine(s.Substring(s.IndexOf(c), m));
            // E: starting from a known substring within the string and of m length.
            Console.WriteLine(s.Substring(s.IndexOf(z), m));
        }
    }
}

As of C# 8, we can use the Range syntax. Cases B and C can be written more succinctly.

// B: starting from n characters in, up to the end of the string;
Console.WriteLine(s[n..]);
// C: whole string minus the last character;
Console.WriteLine(s[..^1]);

Clojure

(def string "alphabet")
(def n 2)
(def m 4)
(def len (count string))

;starting from n characters in and of m length;
(println
 (subs string n (+ n m)))              ;phab
;starting from n characters in, up to the end of the string;
(println
 (subs string n))                      ;phabet
;whole string minus last character;
(println
 (subs string 0 (dec len)))            ;alphabe
;starting from a known character within the string and of m length;
(let [pos (.indexOf string (int \l))]
  (println
   (subs string pos (+ pos m))))     ;lpha
;starting from a known substring within the string and of m length.
(let [pos (.indexOf string "ph")]
  (println
   (subs string pos (+ pos m))))      ;phab

COBOL

       identification division.
       program-id. substring.

       environment division.
       configuration section.
       repository.
           function all intrinsic.

       data division.
       working-storage section.
       01 original.
          05 value "this is a string".
       01 starting  pic 99 value 3.
       01 width     pic 99 value 8.
       01 pos       pic 99.
       01 ender     pic 99.
       01 looking   pic 99.
       01 indicator pic x.
          88 found  value high-value when set to false is low-value.
       01 look-for  pic x(8).

       procedure division.
       substring-main.

       display "Original |" original "|, n = " starting " m = " width
       display original(starting : width)
       display original(starting :)
       display original(1 : length(original) - 1)

       move "a" to look-for
       move 1 to looking
       perform find-position
       if found
           display original(pos : width)
       end-if

       move "is a st" to look-for
       move length(trim(look-for)) to looking
       perform find-position
       if found
           display original(pos : width)
       end-if
       goback.

       find-position.
       set found to false
       compute ender = length(original) - looking
       perform varying pos from 1 by 1 until pos > ender
           if original(pos : looking) equal look-for then
               set found to true
               exit perform
           end-if
       end-perform
       .

       end program substring.
Output:
prompt$ cobc -xj substring.cob
Original |this is a string|, n = 03 m = 08
is is a
is is a string
this is a strin
a string
is a str

ColdFusion

Classic tag based CFML

<cfoutput>
	<cfset str = "abcdefg">
	<cfset n = 2>
	<cfset m = 3>

	<!--- Note: In CF index starts at 1 rather than 0
	starting from n characters in and of m length --->
	#mid( str, n, m )#
	<!--- starting from n characters in, up to the end of the string --->
	<cfset countFromRight = Len( str ) - n + 1>
	#right( str, countFromRight )#
	<!--- whole string minus last character --->
	<cfset allButLast = Len( str ) - 1>
	#left( str, allButLast )#
	<!--- starting from a known character within the string and of m length --->
	<cfset startingIndex = find( "b", str )>
	#mid( str, startingIndex, m )#
	<!--- starting from a known substring within the string and of m length --->
	<cfset startingIndexSubString = find( "bc", str )>
	#mid( str, startingIndexSubString, m )#

</cfoutput>
Output:
bcd
bcdefg
abcdef
bcd
bcd

Script Based CFML

<cfscript>
	str="abcdefg";
	n = 2;
	m = 3;

	// Note: In CF index starts at 1 rather than 0
	// starting from n characters in and of m length
	writeOutput( mid( str, n, m ) );
	// starting from n characters in, up to the end of the string
	countFromRight = Len( str ) - n + 1;
	writeOutput( right( str, countFromRight ) );
	// whole string minus last character
	allButLast = Len( str ) - 1;
	writeOutput( left( str, allButLast ) );
	// starting from a known character within the string and of m length
	startingIndex = find( "b", str );
	writeOutput( mid( str, startingIndex, m ) );
	// starting from a known substring within the string and of m length
	startingIndexSubString = find( "bc", str );
	writeOutput( mid( str, startingIndexSubString, m ) );
</cfscript>
Output:
bcd
bcdefg
abcdef
bcd
bcd

Common Lisp

(let ((string "0123456789")
      (n 2)
      (m 3)
      (start #\5)
      (substring "34"))
  (list (subseq string n (+ n m))
        (subseq string n)
        (subseq string 0 (1- (length string)))
        (let ((pos (position start string)))
          (subseq string pos (+ pos m)))
        (let ((pos (search substring string)))
          (subseq string pos (+ pos m)))))

Component Pascal

BlackBox Component Builder

MODULE Substrings;
IMPORT StdLog,Strings;

PROCEDURE Do*;
CONST
	aStr = "abcdefghijklmnopqrstuvwxyz";
VAR
	str: ARRAY 128 OF CHAR;
	pos: INTEGER;
BEGIN
	Strings.Extract(aStr,3,10,str);
	StdLog.String("from 3, 10 characters:> ");StdLog.String(str);StdLog.Ln;
	Strings.Extract(aStr,3,LEN(aStr) - 3,str);
	StdLog.String("from 3, until the end:> ");StdLog.String(str);StdLog.Ln;
	Strings.Extract(aStr,0,LEN(aStr) - 1,str);
	StdLog.String("whole string but last:> ");StdLog.String(str);StdLog.Ln;
	Strings.Find(aStr,'d',0,pos);
	Strings.Extract(aStr,pos + 1,10,str);
	StdLog.String("from 'd', 10 characters:> ");StdLog.String(str);StdLog.Ln;
	Strings.Find(aStr,"de",0,pos);
	Strings.Extract(aStr,pos + LEN("de"),10,str);
	StdLog.String("from 'de', 10 characters:> ");StdLog.String(str);StdLog.Ln;
END Do;

END Substrings.

Execute: ^Q Substrings.Do

Output:
from 3, 10 characters:> defghijklm
from 3, until the end:> defghijklmnopqrstuvwxyz
whole string but last:> abcdefghijklmnopqrstuvwxy
from 'd', 10 characters:> efghijklmn
from 'de', 10 characters:> fghijklmno

Crystal

def substring_demo(string, n, m, known_character, known_substring)
    n -= 1

    puts string[n...n+m]

    puts string[n...]

    puts string.rchop

    known_character_index = string.index(known_character).not_nil!
    puts string[known_character_index...known_character_index+m]

    known_substring_index = string.index(known_substring).not_nil!
    puts string[known_substring_index...known_substring_index+m]
end

substring_demo("crystalline", 3, 5, 't', "st")
Output:
ystal
ystalline
crystallin
talli
stall

D

Works with: D version 2
import std.stdio, std.string;

void main() {
    const s = "the quick brown fox jumps over the lazy dog";
    enum n = 5, m = 3;

    writeln(s[n .. n + m]);

    writeln(s[n .. $]);

    writeln(s[0 .. $ - 1]);

    const i = s.indexOf("q");
    writeln(s[i .. i + m]);

    const j = s.indexOf("qu");
    writeln(s[j .. j + m]);
}
Output:
uic
uick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog
qui
qui

DBL

;starting from n characters in and of m length;
SUB_STR = STR(n:m)
 
;starting from n characters in, up to the end of the string;
SUB_STR = STR(n,$LEN(STR))
 
;whole string minus last character;
SUB_STR = STR(1,%TRIM(STR)-1)
 
;starting from a known character f within the string and of m length;
;starting from a known substring f within the string and of m length.
SUB_STR = STR(%INSTR(1,STR,f):m)

Delphi

program ShowSubstring;

{$APPTYPE CONSOLE}

uses SysUtils;

const
  s = '0123456789';
  n = 3;
  m = 4;
  c = '2';
  sub = '456';
begin
  Writeln(Copy(s, n, m));             // starting from n characters in and of m length;
  Writeln(Copy(s, n, Length(s)));     // starting from n characters in, up to the end of the string;
  Writeln(Copy(s, 1, Length(s) - 1)); // whole string minus last character;
  Writeln(Copy(s, Pos(c, s), m));     // starting from a known character within the string and of m length;
  Writeln(Copy(s, Pos(sub, s), m));   // starting from a known substring within the string and of m length.
end.
Output:
2345
23456789
012345678
2345
4567

Dyalect

let s = "0123456789"
let n = 3
let m = 2
let c = '3'
let z = "345"
 
// A: starting from n characters in and of m length;
print(s.Substring(n, m))
// B: starting from n characters in, up to the end of the string;
print(s[n..])
// C: whole string minus the last character;
print(s[..-1])
// D: starting from a known character within the string and of m length;
print(s.Substring(s.IndexOf(c),m))
// E: starting from a known substring within the string and of m length.
print(s.Substring(s.IndexOf(z),m))

E

def string := "aardvarks"
def n := 4
def m := 4
println(string(n, n + m))
println(string(n))
println(string(0, string.size() - 1))
println({string(def i := string.indexOf1('d'), i + m)})
println({string(def i := string.startOf("ard"), i + m)})
Output:
vark
varks
aardvark
dvar
ardv

EasyLang

a$ = timestr systime
print substr a$ 12 5
print substr a$ 12 99
#
a$ = "Hallo Österreich!"
print substr a$ 1 (len a$ - 1)
#
c$ = "Ö"
m = 2
i = 1
while substr a$ i 1 <> c$
   i += 1
.
print substr a$ i m
#
c$ = "re"
m = 5
i = 1
while substr a$ i len c$ <> c$
   i += 1
.
print substr a$ i m

ECL

/* In this task display a substring:
   
1.       starting from n characters in and of m length;
2.       starting from n characters in, up to the end of the string;
3.       whole string minus last character;
4.       starting from a known character within the string and of m length;
5.       starting from a known substring within the string and of m length. 
*/

IMPORT STD; //imports a standard string library	
	
TheString := 'abcdefghij';
CharIn    := 3; //n
StrLength := 4; //m
KnownChar := 'f';
KnownSub  := 'def'; 	
FindKnownChar := STD.Str.Find(TheString, KnownChar,1);
FindKnownSub  := STD.Str.Find(TheString, KnownSub,1);
	
OUTPUT(TheString[Charin..CharIn+StrLength-1]); //task1	
OUTPUT(TheString[Charin..]);                   //task2
OUTPUT(TheString[1..LENGTH(TheString)-1]);     //task3
OUTPUT(TheString[FindKnownChar..FindKnownChar+StrLength-1]);//task4
OUTPUT(TheString[FindKnownSub..FindKnownSub+StrLength-1]);  //task5	

/* OUTPUTS:
   defg
   cdefghij	
   abcdefghi
   fghi
   defg	
*/

Ecstasy

module Substrings {
    void run(String[] args = []) {
        @Inject Console console;
        if (args.size < 4) {
            console.print(
                $|
                 |Usage:
                 |
                 |  xec Substrings <str> <offset> <count> <substr>
                 |
            );
            return;
        }

        String s   = args[0];
        Int    n   = new Int(args[1]);
        Int    m   = new Int(args[2]);
        String sub = args[3];
        Char   c   = sub[0];

        console.print($|
                       |{s                   .quoted()=}
                       |{substring(s, n, m  ).quoted()=}
                       |{substring(s, n     ).quoted()=}
                       |{substring(s        ).quoted()=}
                       |{substring(s, c, m  ).quoted()=}
                       |{substring(s, sub, m).quoted()=}
                       |
                     );
    }

    // starting from n characters in and of m length
    static String substring(String s, Int n, Int m) {
        assert 0 <= n <= n+m;
        return n < s.size ? s[n..<(n+m).notGreaterThan(s.size)] : "";
    }

    // starting from n characters in, up to the end of the string
    static String substring(String s, Int n) {
        assert 0 <= n;
        return s.substring(n);
    }

    // whole string minus the last character
    static String substring(String s) {
        return s.size > 1 ? s[0..<s.size-1] : "";
    }

    // starting from a known character within the string and of m length
    static String substring(String s, Char c, Int m){
        assert 0 <= m;
        return substring(s, s.indexOf(c) ?: 0, m);
    }

    // starting from a known substring within the string and of m length
    static String substring(String s, String sub, Int m){
        assert 0 <= m;
        return substring(s, s.indexOf(sub) ?: 0, m);
    }
}
Output:
x$ xec doc/examples/Substrings scaryaardvark 5 4 ard

s                   .quoted()="scaryaardvark"
substring(s, n, m  ).quoted()="aard"
substring(s, n     ).quoted()="aardvark"
substring(s        ).quoted()="scaryaardvar"
substring(s, c, m  ).quoted()="arya"
substring(s, sub, m).quoted()="ardv"

ed

# by Artyom Bologov
H
t0
t0
t0
t0
1s/..\(.\{2\}\).*/\1/
2s/..\(.*\)/\1/
3s/.$//
4s/.*\(c.\{2\}\).*/\1/
5s/.*\(cd.\{3\}\).*/\1/
,p
Q
Output:
$ ed -s substring.input < substring.ed 
Newline appended
cd
cdefgh
abcdefg
cde
cdefg

Eero

#import <Foundation/Foundation.h>

int main()
  autoreleasepool
    str := 'abcdefgh'
    n := 2
    m := 3 
    Log( '%@', str[0 .. str.length-1] )                     // abcdefgh
    Log( '%@', str[n .. m]            )                     // cd
    Log( '%@', str[n .. str.length-1] )                     // cdefgh
    Log( '%@', str.substringFromIndex: n                  ) // cdefgh
    Log( '%@', str[(str.rangeOfString:'b').location .. m] ) // bcd
  return 0

Eiffel

Github Test code

Explainer video - 2 mins

Substring feature explainer video - 1 min

Each task in the description is coded with one or two lines of setup and then a pair of assertions to ensure that the proper result from the substring call. Because the {STRING} class in Eiffel is high-level, it covers both 8-bit and 32-bit strings (ASC and Unicode). If one wants to specifically code for Unicode, all one really needs to do is use {STRING_32} in the space of {STRING}.

class
	RC_SUBSTRING_TEST_SET

inherit
	TEST_SET_SUPPORT

feature -- Test routines

	rc_substring_test
			-- New test routine
		note
			task: "[
				Display a substring:

				- starting from   n   characters in and of   m   length;
				- starting from   n   characters in,   up to the end of the string;
				- whole string minus the last character;
				- starting from a known   character   within the string and of   m   length;
				- starting from a known   substring   within the string and of   m   length.
				]"
			testing:
				"execution/isolated",
				"execution/serial"
			local
				str, str2: STRING
				n, m: INTEGER
			do
				str := "abcdefgh"

				m := 2

					-- starting from   n   characters in and of   m   length;
				n := str.index_of ('e', 1)
				str2 := str.substring (n, n + m - 1)
				assert_strings_equal ("start_n", "ef", str2)
				assert_integers_equal ("m_length_1", 2, str2.count)

					-- starting from   n   characters in,   up to the end of the string;
				str2 := str.substring (n, n + (str.count - n))
				assert_strings_equal ("start_n_to_end", "efgh", str2)
				assert_integers_equal ("len_1a", 4, str2.count)

					-- whole string minus the last character;
				str2 := str.substring (1, str.count - 1)
				assert_strings_equal ("one_less_than_whole", "abcdefg", str2)
				assert_integers_equal ("len_1b", 7, str2.count)

					-- starting from a known   character   within the string and of   m   length;
				n := str.index_of ('d', 1)
				str2 := str.substring (n, n + m - 1)
				assert_strings_equal ("known_char", "de", str2)
				assert_integers_equal ("m_length_2", 2, str2.count)

					-- starting from a known   substring   within the string and of   m   length.
				n := str.substring_index ("bc", 1)
				str2 := str.substring (n, n + m - 1)
				assert_strings_equal ("known_substr", "bc", str2)
				assert_integers_equal ("m_length_3", 2, str2.count)
			end

end

Elena

ELENA 4.x :

import extensions;
 
public program()
{
    var s := "0123456789";
    var n := 3;
    var m := 2;
    var c := $51;
    var z := "345";
 
    console.writeLine(s.Substring(n, m));
    console.writeLine(s.Substring(n, s.Length - n));
    console.writeLine(s.Substring(0, s.Length - 1));
    console.writeLine(s.Substring(s.indexOf(0, c), m));
    console.writeLine(s.Substring(s.indexOf(0, z), m))
}
Output:
34
3456789
012345678
34
34

Elixir

s = "abcdefgh"
String.slice(s, 2, 3)           #=> "cde"
String.slice(s, 1..3)           #=> "bcd"
String.slice(s, -3, 2)          #=> "fg"
String.slice(s, 3..-1)          #=> "defgh"

# UTF-8
s = "αβγδεζηθ"
String.slice(s, 2, 3)           #=> "γδε"
String.slice(s, 1..3)           #=> "βγδ"
String.slice(s, -3, 2)          #=> "ζη"
String.slice(s, 3..-1)          #=> "δεζηθ"

Erlang

Interactive session in Erlang shell showing built in functions doing the task.

1> N = 3.            
2> M = 5.
3> string:sub_string( "abcdefghijklm", N ).
"cdefghijklm"
4> string:sub_string( "abcdefghijklm", N, N + M - 1 ).
"cdefg"
6> string:sub_string( "abcdefghijklm", 1, string:len("abcdefghijklm") - 1 ).
"abcdefghijkl"
7> Start_character = string:chr( "abcdefghijklm", $e ).
8> string:sub_string( "abcdefghijklm", Start_character, Start_character + M - 1 ).
"efghi"
9> Start_string = string:str( "abcdefghijklm", "efg" ).
10> string:sub_string( "abcdefghijklm", Start_string, Start_string + M - 1 ).
"efghi"

Euphoria

sequence baseString, subString, findString
integer findChar
integer m, n

baseString = "abcdefghijklmnopqrstuvwxyz"

-- starting from n characters in and of m length;
n = 12
m = 5
subString = baseString[n..n+m-1]
puts(1, subString )
puts(1,'\n')

-- starting from n characters in, up to the end of the string;
n = 12
subString = baseString[n..$]
puts(1, subString )
puts(1,'\n')

-- whole string minus last character;
subString = baseString[1..$-1]
puts(1, subString )
puts(1,'\n')

-- starting from a known character within the string and of m length;
findChar = 'o'
m = 5
n = find(findChar,baseString)
subString = baseString[n..n+m-1]
puts(1, subString )
puts(1,'\n')

-- starting from a known substring within the string and of m length.
findString = "pq"
m = 5
n = match(findString,baseString)
subString = baseString[n..n+m-1]
puts(1, subString )
puts(1,'\n')
Output:
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
opqrs
pqrst

F#

[<EntryPoint>]
let main args =
    let s = "一二三四五六七八九十"
    let n, m  = 3, 2
    let c = '六'
    let z = "六七八"

    printfn "%s" (s.Substring(n, m))
    printfn "%s" (s.Substring(n))
    printfn "%s" (s.Substring(0, s.Length - 1))
    printfn "%s" (s.Substring(s.IndexOf(c), m))
    printfn "%s" (s.Substring(s.IndexOf(z), m))
    0
Output:
四五
四五六七八九十
一二三四五六七八九
六七
六七

Factor

USING: math sequences kernel ;

! starting from n characters in and of m length
: subseq* ( from length seq -- newseq ) [ over + ] dip subseq ;

! starting from n characters in, up to the end of the string
: dummy ( seq n -- tailseq ) tail ;

! whole string minus last character
: dummy1 ( seq -- headseq ) but-last ;

USING: fry sequences kernel ;
! helper word
: subseq-from-* ( subseq len seq quot -- seq ) [ nip ] prepose 2keep subseq* ; inline

! starting from a known character within the string and of m length;
: subseq-from-char ( char len seq -- seq ) [ index ] subseq-from-* ;

! starting from a known substring within the string and of m length. 
: subseq-from-seq ( subseq len seq -- seq ) [ start ] subseq-from-* ;

Falcon

VBA/Python programmer's approach not sure if it's the most falconic way

/* created by Aykayayciti Earl Lamont Montgomery
April 9th, 2018 */
s = "FalconPL is not just a multi-paradign language but also fun"
n = 12
m = 5

> "starting from n characters in and of m length: ", s[n:n+m]
> "starting from n characters in, up to the end of the string: ", s[n:]
> "whole string minus last character: ", s[0:len(s)-1]
new_n = s.find("j", 0)
> "starting from a known character within the string and of m length: ", s[new_n:new_n+m]
new_n = s.find("mu", 0)
> "starting from a known character within the string and of m length: ", s[new_n:new_n+m]
Output:
starting from n characters in and of m length: not j
starting from n characters in, up to the end of the string: not just a multi-paradign language but also fun
whole string minus last character: FalconPL is not just a multi-paradign language but also fu
starting from a known character within the string and of m length: just 
starting from a known character within the string and of m length: multi
[Finished in 2.3s]

Forth

/STRING and SEARCH are standard words. SCAN is widely implemented. Substrings represented by address/length pairs require neither mutation nor allocation.

2 constant Pos
3 constant Len
: Str ( -- c-addr u )  s" abcdefgh" ;

Str Pos /string drop Len type    \ cde
Str Pos /string type             \ cdefgh
Str 1- type                      \ abcdefg
Str char d scan drop Len type    \ def
Str s" de" search 2drop Len type \ def

Fortran

Works with: Fortran version 90 and later
program test_substring

  character (*), parameter :: string = 'The quick brown fox jumps over the lazy dog.'
  character (*), parameter :: substring = 'brown'
  character    , parameter :: c = 'q'
  integer      , parameter :: n = 5
  integer      , parameter :: m = 15
  integer                  :: i

! Display the substring starting from n characters in and of length m.
  write (*, '(a)') string (n : n + m - 1)
! Display the substring starting from n characters in, up to the end of the string.
  write (*, '(a)') string (n :)
! Display the whole string minus the last character.
  i = len (string) - 1
  write (*, '(a)') string (: i)
! Display the substring starting from a known character and of length m.
  i = index (string, c)
  write (*, '(a)') string (i : i + m - 1)
! Display the substring starting from a known substring and of length m.
  i = index (string, substring)
  write (*, '(a)') string (i : i + m - 1)

end program test_substring
Output:
quick brown fox
quick brown fox jumps over the lazy dog.
The quick brown fox jumps over the lazy dog
quick brown fox
brown fox jumps

Note that in Fortran positions inside character strings are one-based, i. e. the first character is in position one.

Free Pascal

s[n..n+m]
s[n..high(nativeUInt)]
s[1..length(s)-1]
s[pos(c, s)..pos(c, s)+m]
s[pos(p, s)..pos(p, s)+m]

Frink

Although Frink runs on a Java Virtual Machine (JVM), its string operations like substr or indexOf do not have the broken behavior of Java on high Unicode characters. These return correct values for all Unicode codepoints.

String indices are zero-based.

test = "🐱abcdefg😾"
n = 3
m = 2
println[substrLen[test, n, m]]
println[right[test, -m]]
println[left[test, -1]]
pos = indexOf["c"]
if pos != -1
    println[substrLen[test, pos, m]]
pos = indexOf[test, "cd"]
if pos != -1
    println[substrLen[test, pos, m]]
Output:
cd
bcdefg😾
🐱abcdefg
cd
cd

GAP

LETTERS;
# "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
LETTERS{[5 .. 10]};
# "EFGHIJ"

Go

ASCII

The task originally had no mention of unicode. This solution works with ASCII data.

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "ABCDEFGH"
    n, m := 2, 3
    // for reference
    fmt.Println("Index: ", "01234567")
    fmt.Println("String:", s)
    // starting from n characters in and of m length
    fmt.Printf("Start %d, length %d:    %s\n", n, m, s[n : n+m])
    // starting from n characters in, up to the end of the string
    fmt.Printf("Start %d, to end:      %s\n", n, s[n:])
    // whole string minus last character
    fmt.Printf("All but last:         %s\n", s[:len(s)-1])
    // starting from a known character within the string and of m length
    dx := strings.IndexByte(s, 'D')
    fmt.Printf("Start 'D', length %d:  %s\n", m, s[dx : dx+m])
    // starting from a known substring within the string and of m length
    sx := strings.Index(s, "DE")
    fmt.Printf(`Start "DE", length %d: %s`+"\n", m, s[sx : sx+m])
}
Output:
Index:  01234567
String: ABCDEFGH
Start 2, length 3:    CDE
Start 2, to end:      CDEFGH
All but last:         ABCDEFG
Start 'D', length 3:  DEF
Start "DE", length 3: DEF

UTF-8

Strings are generally handled as UTF-8 in Go.

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "αβγδεζηθ"
    r := []rune(s)
    n, m := 2, 3
    kc := 'δ'  // known character
    ks := "δε" // known string
    // for reference
    fmt.Println("Index: ", "01234567")
    fmt.Println("String:", s)
    // starting from n characters in and of m length
    fmt.Printf("Start %d, length %d:    %s\n", n, m, string(r[n:n+m]))
    // starting from n characters in, up to the end of the string
    fmt.Printf("Start %d, to end:      %s\n", n, string(r[n:]))
    // whole string minus last character
    fmt.Printf("All but last:         %s\n", string(r[:len(r)-1]))
    // starting from a known character within the string and of m length
    dx := strings.IndexRune(s, kc)
    fmt.Printf("Start %q, length %d:  %s\n", kc, m, string([]rune(s[dx:])[:m]))
    // starting from a known substring within the string and of m length
    sx := strings.Index(s, ks)
    fmt.Printf("Start %q, length %d: %s\n", ks, m, string([]rune(s[sx:])[:m]))
}
Output:
Index:  01234567
String: αβγδεζηθ
Start 2, length 3:    γδε
Start 2, to end:      γδεζηθ
All but last:         αβγδεζη
Start 'δ', length 3:  δεζ
Start "δε", length 3: δεζ

Groovy

Strings in Groovy are 0-indexed.

def str = 'abcdefgh'
def n = 2
def m = 3
// #1
println str[n..n+m-1]
/* or */
println str[n..<(n+m)]
// #2
println str[n..-1]
// #3
println str[0..-2]
// #4
def index1 = str.indexOf('d')
println str[index1..index1+m-1]
/* or */
println str[index1..<(index1+m)]
// #5
def index2 = str.indexOf('de')
println str[index2..index2+m-1]
/* or */
println str[index2..<(index2+m)]

Haskell

Strings

Works with: Haskell version 6.10.4

A string in Haskell is a list of chars: [Char]

  • The first three tasks are simply:
*Main> take 3 $ drop 2 "1234567890"
"345"

*Main> drop 2 "1234567890"
"34567890"

*Main> init "1234567890"
"123456789"
  • The last two can be formulated with the following function:
t45 n c s | null sub = []
          | otherwise = take n. head $ sub
  where sub = filter(isPrefixOf c) $ tails s
*Main> t45 3 "4" "1234567890"
"456"

*Main> t45 3 "45" "1234567890"
"456"

*Main> t45 3 "31" "1234567890"
""

Data.Text

Testing with an extended set of characters, and using Data.Text functions, including breakOn:

Works with: Haskell version 8.0.2
{-# LANGUAGE OverloadedStrings #-}

import qualified Data.Text as T (Text, take, drop, init, breakOn)
import qualified Data.Text.IO as O (putStrLn)

fromMforN :: Int -> Int -> T.Text -> T.Text
fromMforN n m s = T.take m (T.drop n s)

fromNtoEnd :: Int -> T.Text -> T.Text
fromNtoEnd = T.drop

allButLast :: T.Text -> T.Text
allButLast = T.init

fromCharForN, fromStringForN :: Int -> T.Text -> T.Text -> T.Text
fromCharForN m needle haystack = T.take m $ snd $ T.breakOn needle haystack

fromStringForN = fromCharForN

-- TEST ---------------------------------------------------
main :: IO ()
main =
  mapM_
    O.putStrLn
    ([ fromMforN 9 10
     , fromNtoEnd 20
     , allButLast
     , fromCharForN 6 "话"
     , fromStringForN 6 "大势"
     ] <*>
     ["天地不仁仁者人也🐒话说天下大势分久必合🍑合久必分🔥"])
Output:
话说天下大势分久必合
合久必分🔥
天地不仁仁者人也🐒话说天下大势分久必合🍑合久必分
话说天下大势
大势分久必合

HicEst

CHARACTER :: string = 'ABCDEFGHIJK', known = 'B',  substring = 'CDE'
REAL, PARAMETER :: n = 5,  m = 8
 
WRITE(Messagebox) string(n : n + m - 1), "| substring starting from n, length m"
WRITE(Messagebox) string(n :), "| substring starting from n, to  end of string"
WRITE(Messagebox) string(1: LEN(string)-1), "| whole string minus last character"

pos_known = INDEX(string, known)
WRITE(Messagebox) string(pos_known : pos_known+m-1), "| substring starting from pos_known, length m"

pos_substring = INDEX(string, substring)
WRITE(Messagebox) string(pos_substring : pos_substring+m-1), "| substring starting from pos_substring, length m"

Icon and Unicon

procedure main(arglist)
write("Usage: substring  <string> <first position> <second position> <single character> <substring>")
s := \arglist[1] | "aardvarks"
n := \arglist[2] | 5 
m := \arglist[3] | 4
c := \arglist[4] | "d"
ss := \arglist[5] | "ard"

write( s[n+:m] )           
write( s[n:0] )                          
write( s[1:-1] )                    
write( s[find(c,s)+:m] )        
write( s[find(ss,s)+:m] )     
end

J

   5{.3}.'Marshmallow'
shmal
   3}.'Marshmallow'
shmallow
   }.'Marshmallow'
arshmallow
   }:'Marshmallow'
Marshmallo
   5{.(}.~ i.&'m')'Marshmallow'
mallo
   5{.(}.~ I.@E.~&'sh')'Marshmallow'
shmal

Note that there are other, sometimes better, ways of accomplishing this task.

   'Marshmallow'{~(+i.)/3 5
shmal

Or, probably more efficient when the desired substring is large:

   (,.3 5)];.0 'Marshmallow'
shmal

The taketo / takeafter and dropto / dropafter utilities from the strings script further simplify these types of tasks.

   require 'strings'
   'sh' dropto 'Marshmallow'
shmallow
   5{. 'sh' dropto 'Marshmallow'
shmal
   'sh' takeafter 'Marshmallow'
mallow

Note also that these operations work the same way on lists of numbers that they do on this example list of characters.

   3}. 2 3 5 7 11 13 17 19
7 11 13 17 19
   7 11 dropafter 2 3 5 7 11 13 17 19
2 3 5 7 11

Java

public static String Substring(String str, int n, int m){
    return str.substring(n, n+m);
}
public static String Substring(String str, int n){
    return str.substring(n);
}
public static String Substring(String str){
    return str.substring(0, str.length()-1);
}
public static String Substring(String str, char c, int m){
    return str.substring(str.indexOf(c), str.indexOf(c)+m+1);
}
public static String Substring(String str, String sub, int m){
    return str.substring(str.indexOf(sub), str.indexOf(sub)+m+1);
}

JavaScript

The String object has two similar methods: substr and substring.

  • substr(start, [len]) returns a substring beginning at a specified location and having a specified length.
  • substring(start, [end]) returns a string containing the substring from start up to, but not including, end.
var str = "abcdefgh";

var n = 2;
var m = 3;

//  *  starting from n characters in and of m length;
str.substr(n, m);  // => "cde"

//  * starting from n characters in, up to the end of the string;
str.substr(n);  // => "cdefgh"
str.substring(n);  // => "cdefgh"

//  * whole string minus last character;
str.substring(0, str.length - 1);  // => "abcdefg"

//  * starting from a known character within the string and of m length;
str.substr(str.indexOf('b'), m);  // => "bcd"

//  * starting from a known substring within the string and of m length. 
str.substr(str.indexOf('bc'), m);  // => "bcd"


Or, in terms of some familiar functional primitives, translating broadly from Haskell:

(function () {
    'use strict';

    //  take :: Int -> Text -> Text
    function take(n, s) {
        return s.substr(0, n);
    }

    //  drop :: Int -> Text -> Text
    function drop(n, s) {
        return s.substr(n);
    }


    // init :: Text -> Text
    function init(s) {
        var n = s.length;
        return (n > 0 ? s.substr(0, n - 1) : undefined);
    }
    
    // breakOn :: Text -> Text -> (Text, Text)
    function breakOn(strPattern, s) {
        var i = s.indexOf(strPattern);
        return i === -1 ? [strPattern, ''] : [s.substr(0, i), s.substr(i)];
    }
    

    var str = '一二三四五六七八九十';


    return JSON.stringify({
    
        'from n in, of m length': (function (n, m) {
            return take(m, drop(n, str));
        })(4, 3),
        
        
        'from n in, up to end' :(function (n) {
            return drop(n, str);
        })(3),
        
        
        'all but last' : init(str),
        
        
        'from matching char, of m length' : (function (pattern, s, n) {
            return take(n, breakOn(pattern, s)[1]);
        })('五', str, 3),
        
        
        'from matching string, of m length':(function (pattern, s, n) {
            return take(n, breakOn(pattern, s)[1]);
        })('六七', str, 4)
        
    }, null, 2);

})();
Output:
{
  "from n in, of m length": "五六七",
  "from n in, up to end": "四五六七八九十",
  "all but last": "一二三四五六七八九",
  "from matching char, of m length": "五六七",
  "from matching string, of m length": "六七八九"
}

jq

Works with: jq version 1.4

For this exercise we use the Chinese characters for 1 to 10, the character for "10" being "十":

def s: "一二三四五六七八九十";

jq strings are UTF-8 strings, and array-based string indexing and most string functions, such as length/0, are based on Unicode code points. However, the function index/1 currently uses character counts when its input is a string, and therefore in the following we use ix/1 defined as follows:

def ix(s): explode | index(s|explode);

(Users who have access to the regex function match/1 can use it, as illustrated in the comments below.)

Since jq arrays and strings have an index origin of 0, "n characters in" is interpreted to require an index of (n+1).

# starting from n characters in and of m length:  .[n+1: n+m+1]
"s[1:2] => \( s[1:2] )",
  
# starting from n characters in, up to the end of the string:  .[n+1:]
"s[9:] => \( s[9:] )",

# whole string minus last character: .[0:length-1]
"s|.[0:length-1] => \(s | .[0:length-1] )",

# starting from a known character within the string and of m length:
  # jq 1.4: ix(c) as $i | .[ $i: $i + m]
  # jq>1.4: match(c).offset as $i | .[ $i: $i + m]
"s | ix(\"五\") as $i | .[$i: $i + 1] => \(s | ix("五") as $i | .[$i: $i + 1] )",


# starting from a known substring within the string and of m length:
  # jq 1.4: ix(sub) as $i | .[ $i: $i + m]
  # jq>1.4: match(sub).offset as $i | .[ $i: $i + m]
"s | ix(\"五六\") as $i | .[$i: $i + 2] => " +
 "\( s | ix("五六") as $i | .[$i: $i + 2] )"
Output:
$ jq -M -n -r -f Substring.jq
s[1:2] => 二
s[9:] => 十
s|.[0:length-1] => 一二三四五六七八九
s | ix("五") as $i | .[$i: $i + 1] => 五
s | ix("五六") as $i | .[$i: $i + 2] => 五六

Jsish

Translation of: Javascript
#!/usr/local/bin/jsish -u %s

var str = "abcdefgh";
 
var n = 2;
var m = 3;

// In jsish, semi-colon first character lines are echoed with result
;str;
;n;
;m;

//  *  starting from n characters in and of m length;
;str.substr(n, m);
 
//  * starting from n characters in, up to the end of the string;
;str.substr(n);
;str.substring(n);
 
//  * whole string minus last character;
;str.substring(0, str.length - 1);
 
//  * starting from a known character within the string and of m length;
;str.substr(str.indexOf('b'), m);
 
//  * starting from a known substring within the string and of m length. 
;str.substr(str.indexOf('bc'), m);


/* Functional */
var res = (function () {
    'use strict';
 
    //  take :: Int -> Text -> Text
    function take(n, s) {
        return s.substr(0, n);
    }
 
    //  drop :: Int -> Text -> Text
    function drop(n, s) {
        return s.substr(n);
    }
 
 
    // init :: Text -> Text
    function init(s) {
        var n = s.length;
        return (n > 0 ? s.substr(0, n - 1) : undefined);
    }
 
    // breakOn :: Text -> Text -> (Text, Text)
    function breakOn(strPattern, s) {
        var i = s.indexOf(strPattern);
        return i === -1 ? [strPattern, ''] : [s.substr(0, i), s.substr(i)];
    }
 
 
    var str = 'abcdefgh';
 
 
    return JSON.stringify({
 
        'from 4 in, of 3 length': (function (n, m) {
            return take(m, drop(n, str));
        })(4, 3),
 
 
        'from 3 in, up to end' : (function (n) {
            return drop(n, str);
        })(3),
 
 
        'all but last' : init(str),
 
 
        'from matching b, of length 3' : (function (pattern, s, n) {
            return take(n, breakOn(pattern, s)[1]);
        })('b', str, 3),
 

        'from matching bc, of length 4':(function (pattern, s, n) {
            return take(n, breakOn(pattern, s)[1]);
        })('bc', str, 4)

    }, true);

})();
;res;
Output:
prompt$ jsish --U substringing.jsi
str ==> abcdefgh
n ==> 2
m ==> 3
str.substr(n, m) ==> cde
str.substr(n) ==> cdefgh
str.substring(n) ==> cdefgh
str.substring(0, str.length - 1) ==> abcdefgh
str.substr(str.indexOf('b'), m) ==> bcd
str.substr(str.indexOf('bc'), m) ==> bcd
res ==> { "all but last":"abcdefg", "from 3 in, up to end":"defgh", "from 4 in, of 3 length":"efg", "from matching b, of length 3":"bcd", "from matching bc, of length 4":"bcde" }

prompt$ jsish -u -update true substringing.jsi
Created substringing.jsi

prompt$ jsish -u substringing.jsi
[PASS] substringing.jsi

The initial --U is a run with echo mode. The -u -update true puts jsish in unit test mode, and will add a comparison block. After the test pass, the code file is changed to

#!/usr/local/bin/jsish -u %s

var str = "abcdefgh";
 
var n = 2;
var m = 3;

// In jsish, semi-colon first character lines are echoed with result
;str;
;n;
;m;

//  *  starting from n characters in and of m length;
;str.substr(n, m);
 
//  * starting from n characters in, up to the end of the string;
;str.substr(n);
;str.substring(n);
 
//  * whole string minus last character;
;str.substring(0, str.length - 1);
 
//  * starting from a known character within the string and of m length;
;str.substr(str.indexOf('b'), m);
 
//  * starting from a known substring within the string and of m length. 
;str.substr(str.indexOf('bc'), m);


/* Functional */
var res = (function () {
    'use strict';
 
    //  take :: Int -> Text -> Text
    function take(n, s) {
        return s.substr(0, n);
    }
 
    //  drop :: Int -> Text -> Text
    function drop(n, s) {
        return s.substr(n);
    }
 
 
    // init :: Text -> Text
    function init(s) {
        var n = s.length;
        return (n > 0 ? s.substr(0, n - 1) : undefined);
    }
 
    // breakOn :: Text -> Text -> (Text, Text)
    function breakOn(strPattern, s) {
        var i = s.indexOf(strPattern);
        return i === -1 ? [strPattern, ''] : [s.substr(0, i), s.substr(i)];
    }
 
 
    var str = 'abcdefgh';
 
 
    return JSON.stringify({
 
        'from 4 in, of length 3': (function (n, m) {
            return take(m, drop(n, str));
        })(4, 3),
 
 
        'from 3 in, up to end' : (function (n) {
            return drop(n, str);
        })(3),
 
 
        'all but last' : init(str),
 
 
        'from matching b, of length 3' : (function (pattern, s, n) {
            return take(n, breakOn(pattern, s)[1]);
        })('b', str, 3),
 
 
        'from matching bc, of length 4':(function (pattern, s, n) {
            return take(n, breakOn(pattern, s)[1]);
        })('bc', str, 4)

    }, true);

})();
;res;

/*
=!EXPECTSTART!=
str ==> abcdefgh
n ==> 2
m ==> 3
str.substr(n, m) ==> cde
str.substr(n) ==> cdefgh
str.substring(n) ==> cdefgh
str.substring(0, str.length - 1) ==> abcdefgh
str.substr(str.indexOf('b'), m) ==> bcd
str.substr(str.indexOf('bc'), m) ==> bcd
res ==> { "all but last":"abcdefg", "from 3 in, up to end":"defgh", "from 4 in, of length 3":"efg", "from matching b, of length 3":"bcd", "from matching bc, of length 4":"bcde" }
=!EXPECTEND!=
*/

Julia

By default, the type of the string is infered from its elements. In the example below, the string s is an ASCII string. In order to interpret the string as an UTF8 string with logical access to its argument, one should use CharString("/\ʕ•ᴥ•ʔ/\"...). Without the CharString declaration, the string is interpreted as an UTF8 string with access through its byte representation.

julia> s = "abcdefg"
"abcdefg"

julia> n = 3
3

julia> s[n:end]
"cdefg"

julia> m=2
2

julia> s[n:n+m]
"cde"

julia> s[1:end-1]
"abcdef"

julia> s[search(s,'c')]
'c'

julia> s[search(s,'c'):search(s,'c')+m]
"cde"

Kotlin

Strings in Kotlin are 0-indexed:

// version 1.0.6

fun main(args: Array<String>) {
    val s = "0123456789"
    val n = 3
    val m = 4
    val c = '5'
    val z = "12"
    var i: Int
    println(s.substring(n, n + m))
    println(s.substring(n))
    println(s.dropLast(1))
    i = s.indexOf(c)
    println(s.substring(i, i + m))
    i = s.indexOf(z)
    println(s.substring(i, i + m))
}
Output:
3456
3456789
012345678
5678
1234

Ksh

#!/bin/ksh

# Display a substring:
#	- starting from  n  characters in and of  m  length;
#	- starting from  n  characters in, up to the end of the string;
#	- whole string minus the last character;
#	- starting from a known character within the string and of  m  length;
#	- starting from a known substring within the string and of  m  length.

#	# Variables:
#

str='solve this task according to the task description,'
integer n=6 m=14
ch='v'
substr='acc'

#	# Functions:
#
#	# Function _length(str, start, length) - return substr from start, 
#	# length chars long (length=-1 = end-of-str)
#
function _length {
	typeset _str ; _str="$1"
	typeset _st ; integer _st=$2
	typeset _ln ; integer _ln=$3

	(( _ln == -1 )) && 	echo "${_str:${_st}}"

	echo "${_str:${_st}:${_ln}}"
}

 ######
# main #
 ######
print -- "--String (Length: ${#str} chars):"
print "${str}\n"

print -- "--From char ${n} and ${m} chars in length:"
_length "${str}" ${n} ${m}
echo

print -- "--From char ${n} to the end:"
_length "${str}" ${n} -1

print -- "--Last character removed:"	# Strings in ksh are zero based
_length "${str}" 0 $(( ${#str}-1 ))
echo

print -- "-From char:'${ch}' and ${m} chars in length:"
foo=${str%${ch}*}
_length "${str}" ${#foo} ${m}
echo

print -- "-From substr:'${substr}' and ${m} chars in length:"
foo=${str%${substr}*}
_length "${str}" ${#foo} ${m}
echo
Output:

--String (Length: 50 chars): solve this task according to the task description,

--From char 6 and 14 chars in length: this task acco

--From char 6 to the end: this task according to the task description,

--Last character removed: solve this task according to the task description

-From char:'v' and 14 chars in length: ve this task a

-From substr:'acc' and 14 chars in length: according to t

LabVIEW

To enhance readability, this task was split into two separate GUI's. In the second, note that "Known Substring" can be a single character.
1:  
2:  

Lambdatalk

{S.slice 1 2 hello brave new world}
-> brave new
{W.slice 4 11 www.rosetta.org}
-> rosetta

Lang

$txt = The Lang programming language!

$n = 9
$m = 11

$c = p

$searchTxt = prog

fn.println(fn.substring($txt, $n, parser.op($n + $m)))
# Output: programming

fn.println(fn.substring($txt, $n))
# Output: programming language!

fn.println(fn.substring($txt, 0, parser.op(fn.len($txt) - 1)))
# Output: The Lang programming language

fn.println(fn.substring($txt, fn.indexOf($txt, $c), parser.op(fn.indexOf($txt, $c) + $m)))
# Output: programming

fn.println(fn.substring($txt, fn.indexOf($txt, $searchTxt), parser.op(fn.indexOf($txt, $searchTxt) + $m)))
# Output: programming

Lang5

: cr "\n". ; [] '__A set : dip swap __A swap 1 compress append '__A set execute __A
    -1 extract nip ; : nip swap drop ; : tuck swap over ; : -rot rot rot ; : 0= 0 == ; : 1+ 1 + ;
: 2dip swap 'dip dip ; : 2drop drop drop ; : |a,b> over - iota + ; : bi* 'dip dip execute ; : bi@ dup bi* ;
: comb "" split ; : concat "" join ; : empty? length 0= ; : tail over lensize |a,b> subscript ;
: lensize length nip ; : while do 'dup dip 'execute 2dip rot if dup 2dip else break then loop 2drop ;

: <substr>  comb -rot over + |a,b> subscript concat ;
: str-tail  tail concat ;
: str-index
    : 2streq  2dup over lensize iota subscript eq '* reduce ;
    swap 'comb bi@ length -rot 0 -rot
    "2dup 'lensize bi@ <="
    "2streq if 0 reshape else '1+ 2dip 0 extract drop then"
    while empty? if 2drop tuck == if drop -1 then else 4 ndrop -1 then ;

'abcdefgh 'str set 2 'n set 3 'm set
n m str <substr>
str comb n str-tail
str "d" str-index m str <substr>
str "de" str-index m str <substr>

Lasso

local(str = 'The quick grey rhino jumped over the lazy green fox.')

//starting from n characters in and of m length;
#str->substring(16,5) //rhino

//starting from n characters in, up to the end of the string
#str->substring(16) //rhino jumped over the lazy green fox.

//whole string minus last character
#str->substring(1,#str->size - 1) //The quick grey rhino jumped over the lazy green fox

//starting from a known character within the string and of m length;
#str->substring(#str->find('g'),10) //grey rhino

//starting from a known substring within the string and of m length
#str->substring(#str->find('rhino'),12) //rhino jumped

LFE

Translation of: Erlang

From the LFE REPL:

> (set n 3)
3
> (set m 5)
5
> (string:sub_string "abcdefghijklm" n)
"cdefghijklm"
> (string:sub_string "abcdefghijklm" n (+ n m -1))
"cdefg"
> (string:sub_string "abcdefghijklm" 1 (- (length "abcdefghijklm") 1))
"abcdefghijkl"
> (set char-index (string:chr "abcdefghijklm" #\e))
5
> (string:sub_string "abcdefghijklm" char-index (+ char-index m -1))
"efghi"
> (set start-str (string:str "abcdefghijklm" "efg"))
5
> (string:sub_string "abcdefghijklm" start-str (+ start-str m -1))
"efghi"

Lingo

str = "The quick brown fox jumps over the lazy dog"

-- starting from n characters in and of m length
n = 5
m = 11
put str.char[n..n+m-1]
-- "quick brown"

-- starting from n characters in, up to the end of the string
n = 11
put str.char[n..str.length]
-- "brown fox jumps over the lazy dog"

-- whole string minus last character
put str.char[1..str.length-1]
-- "The quick brown fox jumps over the lazy do"

-- starting from a known character within the string and of m length
c = "x"
m = 7
pos = offset(c, str)
put str.char[pos..pos+m-1]
-- "x jumps"

-- starting from a known substring within the string and of m length
sub = "fox"
m = 9
pos = offset(sub, str)
put str.char[pos..pos+m-1]
-- "fox jumps"

LiveCode

put "pple" into x
answer char 2 to char 5 of x  // n = 2, m=5
answer char 2 to len(x) of x  // n = 2, m = len(x), can also use -1
answer char 1 to -2 of x  // n = 1, m = 1 less than length of string
answer char offset("p",x) to -1 of x // known char "p" to end of string
answer char offset("pl",x) to -1 of x // known "pl" to end of string

n.b. Offset also supports a third parameter "charsToSkip" allowing you to loop through subsequent matches of the substring.

Works with: UCB Logo

The following are defined to behave similarly to the built-in index operator ITEM. As with most Logo list operators, these are designed to work for both words (strings) and lists.

to items :n :thing
  if :n >= count :thing [output :thing]
  output items :n butlast :thing
end

to butitems :n :thing 
  if or :n <= 0 empty? :thing [output :thing]
  output butitems :n-1 butfirst :thing
end

to middle :n :m :thing
  output items :m-(:n-1) butitems :n-1 :thing
end

to lastitems :n :thing
  if :n >= count :thing [output :thing]
 output lastitems :n butfirst :thing
end

to starts.with :sub :thing
  if empty? :sub [output "true]
  if empty? :thing [output "false]
  if not equal? first :sub first :thing [output "false]
  output starts.with butfirst :sub butfirst :thing
end

to members :sub :thing
  output cascade [starts.with :sub ?] [bf ?] :thing
end

; note: Logo indices start at one
make "s "abcdefgh
print items 3 butitems 2 :s ; cde
print middle 3 5  :s   ; cde
print butitems 2  :s   ; cdefgh
print butlast     :s   ; abcdefg
print items 3 member  "d  :s ; def
print items 3 members "de :s ; def

Logtalk

Using atoms for representing strings and usng the same sample data as e.g. in the Java solution:

:- object(substring).

    :- public(test/5).

    test(String, N, M, Character, Substring) :-
        sub_atom(String, N, M, _, Substring1),
        write(Substring1), nl,
        sub_atom(String, N, _, 0, Substring2),
        write(Substring2), nl,
        sub_atom(String, 0, _, 1, Substring3),
        write(Substring3), nl,
        % there can be multiple occurences of the character
        once(sub_atom(String, Before4, 1, _, Character)),
        sub_atom(String, Before4, M, _, Substring4),
        write(Substring4), nl,
        % there can be multiple occurences of the substring
        once(sub_atom(String, Before5, _, _, Substring)),
        sub_atom(String, Before5, M, _, Substring5),
        write(Substring5), nl.

:- end_object.
Output:
| ?- ?- substring::test('abcdefgh', 2, 3, 'b', 'bc').
cde
cdefgh
abcdefg
bcd
bcd
yes

Lua

str = "abcdefghijklmnopqrstuvwxyz"
n, m = 5, 15

print( string.sub( str, n, m ) )    -- efghijklmno
print( string.sub( str, n, -1 ) )   -- efghijklmnopqrstuvwxyz
print( string.sub( str, 1, -2 ) )   -- abcdefghijklmnopqrstuvwxy

pos = string.find( str, "i" )
if pos ~= nil then print( string.sub( str, pos, pos+m ) ) end -- ijklmnopqrstuvwx

pos = string.find( str, "ijk" )
if pos ~= nil then print( string.sub( str, pos, pos+m ) ) end-- ijklmnopqrstuvwx 

-- Alternative (more modern) notation

print ( str:sub(n,m) )         -- efghijklmno
print ( str:sub(n) )           -- efghijklmnopqrstuvwxyz
print ( str:sub(1,-2) )        -- abcdefghijklmnopqrstuvwxy

pos = str:find "i"
if pos then print (str:sub(pos,pos+m)) end -- ijklmnopqrstuvwx 

pos = str:find "ijk"
if pos then print (str:sub(pos,pos+m)) end d-- ijklmnopqrstuvwx

M2000 Interpreter

By default a sting can contain anything, and has a maximum length of 2GBytes. Literals are always UTF-16LE. Print/edit done as UTF-16LE. But we can use Str$(a_string) to convert UTF-16LE to Ansi, using Locale id. To display it we can use Chr$(a_String), to convert back to UTF-16LE. Mid$, Right$, Left$, Instr,RInstr works for Ansi using "as byte". For Utf16-le, we get next 16bit value, not exactly next char, but for many languages it is exactly next char.

Function for length always return length as Words (two bytes), so we can get half, if we have an odd number of ansi characters. For Utf16-le there is another Len function,Len.Disp which returns the needed positions for displaying characters. So Print LEN.DISP("aããz")=4  : Print Len("̃ãz")=4

Module CheckAnsi {
      \\ ANSI STRING
      Locale 1033
      \\ convert UTF16-LE to ANSI 8bit
      s$ =Str$("ABCDEFG")
      Print Len(s$)=3.5  ' 3.5 words, means 7 bytes (3.5*2)
      AnsiLen=Len(s$)*2
      ' From 4th byte get 3 bytes
      n=4
      m=3
      substring$=Mid$(s$, n, m as byte)
      substring2End$=Mid$(s$, n , AnsiLen as byte)
      substringMinusOne$=Left$(s$, AnsiLen-1 as byte)
      substringFromKnownCharacter$=Mid$(s$, Instr(s$, str$("B") as byte) , m as byte)
      substringFromKnownSubstring$=Mid$(s$, Instr(s$, str$("BC") as byte) , m as byte)
      Print Len(substring$)*2=m
      
      \\ convert to UTF-16LE
      Print Chr$(substring$)="DEF"
      Print Chr$(substring2End$)="DEFG"
      Print Chr$(substringMinusOne$)="ABCDEF"
      Print Chr$(substringFromKnownCharacter$)="BCD"
      Print Chr$(substringFromKnownSubstring$)="BCD"
}
CheckAnsi
Module CheckUTF16LE {
      s$ ="ABCDEFG"
      Print Len(s$)=7
      Utf16Len=Len(s$)
      ' From 4th byte get 3 bytes
      n=4
      m=3
      substring$=Mid$(s$, n, m)
      substring2End$=Mid$(s$, n , Utf16Len)
      substringMinusOne$=Left$(s$, Utf16Len-1)
      substringFromKnownCharacter$=Mid$(s$, Instr(s$, "B") , m)
      substringFromKnownSubstring$=Mid$(s$, Instr(s$, "BC") , m)
      Print Len(substring$)=m
      
      \\ convert to UTF-16LE
      Print substring$="DEF"
      Print substring2End$="DEFG"
      Print substringMinusOne$="ABCDEF"
      Print substringFromKnownCharacter$="BCD"
      Print substringFromKnownSubstring$="BCD"
}
CheckUTF16LE

Maple

> n, m := 3, 5:
> s := "The Higher, The Fewer!":
> s[ n .. n + m - 1 ];
                     "e Hig"

There are a few ways to get everything from the n-th character on.

> s[ n .. -1 ] = s[ n .. ];
 "e Higher, The Fewer!" = "e Higher, The Fewer!"

> StringTools:-Drop( s, n - 1 );
              "e Higher, The Fewer!"

There are a few ways to get all but the last character.

> s[ 1 .. -2 ] = s[ .. -2 ];
"The Higher, The Fewer" = "The Higher, The Fewer"

> StringTools:-Chop( s );
             "The Higher, The Fewer"

The searchtext command returns the position of a matching substring.

> pos := searchtext( ",", s ):
> s[ pos .. pos + m - 1 ];
                     ", The"

> pos := searchtext( "Higher", s ):
> s[ pos .. pos + m - 1 ];         
                     "Highe"

But, note that searchtext returns 0 when there is no match, and 0 is not a valid index into a string.

Mathematica /Wolfram Language

The StringTake and StringDrop are relevant for this exercise.

n = 2
m = 3
StringTake["Mathematica", {n+1, n+m-1}]
StringDrop["Mathematica", n]
(* StringPosition returns a list of starting and ending character positions for a substring *)
pos = StringPosition["Mathematica", "e"][[1]][[1]]
StringTake["Mathematica", {pos, pos+m-1}]
(* Similar to above *)
pos = StringPosition["Mathematica", "the"][[1]]
StringTake["Mathematica", {pos, pos+m-1}]

MATLAB / Octave

Unicode, UTF-8, UTF-16 is only partially supported. In some cases, a conversion of unicode2native() or native2unicode() is necessary.

    % starting from n characters in and of m length;
        s(n+(1:m))
        s(n+1:n+m)
    % starting from n characters in, up to the end of the string;
        s(n+1:end)
    % whole string minus last character;
        s(1:end-1)
    % starting from a known character within the string and of m length;
        s(find(s==c,1)+[0:m-1])
    % starting from a known substring within the string and of m length. 
        s(strfind(s,pattern)+[0:m-1])

Maxima

s: "the quick brown fox jumps over the lazy dog";
substring(s, 17);
/* "fox jumps over the lazy dog" */
substring(s, 17, 20);
/* "fox" */

MUMPS

MUMPS has the first position in a string numbered as 1.

SUBSTR(S,N,M,C,K)
 ;show substring operations
 ;S is the string
 ;N is a position within the string (that is, n<length(string))
 ;M is an integer of positions to show
 ;C is a character within the string S
 ;K is a substring within the string S
 ;$Find returns the position after the substring
 NEW X
 WRITE !,"The base string is:",!,?5,"'",S,"'"
 WRITE !,"From position ",N," for ",M," characters:"
 WRITE !,?5,$EXTRACT(S,N,N+M-1)
 WRITE !,"From position ",N," to the end of the string:"
 WRITE !,?5,$EXTRACT(S,N,$LENGTH(S))
 WRITE !,"Whole string minus last character:"
 WRITE !,?5,$EXTRACT(S,1,$LENGTH(S)-1)
 WRITE !,"Starting from character '",C,"' for ",M," characters:"
 SET X=$FIND(S,C)-$LENGTH(C)
 WRITE !,?5,$EXTRACT(S,X,X+M-1)
 WRITE !,"Starting from string '",K,"' for ",M," characters:"
 SET X=$FIND(S,K)-$LENGTH(K)
 W !,?5,$EXTRACT(S,X,X+M-1)
 QUIT

Usage:

USER>D SUBSTR^ROSETTA("ABCD1234efgh",3,4,"D","23")
 
The base string is:
     'ABCD1234efgh'
From position 3 for 4 characters:
     CD12
From position 3 to the end of the string:
     CD1234efgh
Whole string minus last character:
     ABCD1234efg
Starting from character 'D' for 4 characters:
     D123
Starting from string '23' for 4 characters:
     234e

Nanoquery

str = "test string"

println substr(str, m, m + n)
println substr(str, n, len(str))
println substr(str, 0, len(str) - 1)
println substr(str, str.indexOf("s"), str.indexOf("s") + m)
println substr(str, str.indexOf("str"), str.indexOf("str") + m)

Nemerle

using System;
using System.Console;

module Substrings
{
    Main() : void
    {
        string s = "0123456789";
        def n = 3;
        def m = 2;
        def c = '3';
        def z = "345";

        WriteLine(s.Substring(n, m));
        WriteLine(s.Substring(n, s.Length - n));
        WriteLine(s.Substring(0, s.Length - 1));
        WriteLine(s.Substring(s.IndexOf(c,0,s.Length), m));
        WriteLine(s.Substring(s.IndexOf(z, 0, s.Length), m));
    }
}

NetRexx

Translation of: REXX
/* NetRexx */

options replace format comments java crossref savelog symbols

s = 'abcdefghijk'
n = 4
m = 3

say s
say s.substr(n, m)
say s.substr(n)
say s.substr(1, s.length - 1)
say s.substr(s.pos('def'), m) 
say s.substr(s.pos('g'), m)

return
Output:
abcdefghijk
def
defghijk
abcdefghij
def
ghi

newLISP

> (set 'str "alphabet" 'n 2 'm 4)
4
> ; starting from n characters in and of m length
> (slice str n m)
"phab"
> ; starting from n characters in, up to the end of the string
> (slice str n)
"phabet"
> ; whole string minus last character
> (chop str)
"alphabe"
> ; starting from a known character within the string and of m length
> (slice str (find "l" str) m)
"lpha"
> ; starting from a known substring within the string and of m length
> (slice str (find "ph" str) m)
"phab"

Nim

Nim allows to work with raw strings, ignoring the encoding, or with UTF-8 strings. The following program shows how to extract substrings in both cases.

import strformat, strutils, unicode

let
  s1 = "abcdefgh"   # ASCII string.
  s2 = "àbĉdéfgĥ"   # UTF-8 string.
  n = 2
  m = 3
  c = 'd'
  cs1 = "de"
  cs2 = "dé"

var pos: int

# ASCII strings.
# We can take a substring using "s.substr(first, last)" or "s[first..last]".
# The latter form can also be used as value to assign a substring.

echo "ASCII string: ", s1

echo &"Starting from n = {n} characters in and of m = {m} length: ", s1[(n - 1)..(n + m - 2)]
echo &"Starting from n = {n} characters in, up to the end of the string: ", s1[(n - 1)..^1]
echo "Whole string minus the last character: ", s1[0..^2]

pos = s1.find(c)
if pos > 0:
  echo &"Starting from character '{c}' within the string and of m = {m} length: ", s1[pos..<(pos + m)]
else:
  echo &"Character '{c}' not found."

pos = s1.find(cs1)
if pos > 0:
  echo &"Starting from substring “{cs1}” within the string and of m = {m} length: ", s1[pos..<(pos + m)]
else:
  echo &"String “{cs1}” not found."


# UTF-8 strings.

proc findUtf8(s: string; c: char): int =
  ## Return the codepoint index of the first occurrence of a given character in a string.
  ## Return - 1 if not found.
  s.toRunes.find(Rune(c))

proc findUtf8(s1, s2: string): int =
  ## Return the codepoint index of the first occurrence of a given string in a string.
  ## Return - 1 if not found.
  let s1 = s1.toRunes
  let s2 = s2.toRunes
  for i in 0..(s1.len - s2.len):
    if s1[i..(i + s2.len - 1)] == s2: return i
  result = -1

echo()
echo "UTF-8 string: ", s2

echo &"Starting from n = {n} characters in and of m = {m} length: ", s2.runeSubStr(n - 1, m)
echo &"Starting from n = {n} characters in, up to the end of the string: ", s2.runeSubstr(n - 1)
echo "Whole string minus the last character: ", s2.runeSubStr(0, s2.runeLen - 1)

pos = s2.findUtf8(c)
if pos > 0:
  echo &"Starting from character '{c}' within the string and of m = {m} length: ", s2.runeSubStr(pos, m)
else:
  echo &"String “{cs1}” not found."

pos = s2.findUtf8(cs2)
if pos > 0:
  echo &"Starting from substring “{cs2}” within the string and of m = {m} length: ", s2.runeSubStr(pos, m)
else:
  echo &"String “{cs2}” not found."
Output:
ASCII string: abcdefgh
Starting from n = 2 characters in and of m = 3 length: bcd
Starting from n = 2 characters in, up to the end of the string: bcdefgh
Whole string minus the last character: abcdefg
Starting from character 'd' within the string and of m = 3 length: def
Starting from substring “de” within the string and of m = 3 length: def

UTF-8 string: àbĉdéfgĥ
Starting from n = 2 characters in and of m = 3 length: bĉd
Starting from n = 2 characters in, up to the end of the string: bĉdéfgĥ
Whole string minus the last character: àbĉdéfg
Starting from character 'd' within the string and of m = 3 length: déf
Starting from substring “dé” within the string and of m = 3 length: déf

Niue

( based on the JavaScript code )
'abcdefgh 's ;
s str-len 'len ;
2 'n ;
3 'm ;

( starting from n characters in and of m length )
s n n m + substring . ( => cde ) newline

( starting from n characters in, up to the end of the string )
s n len substring . ( => cdefgh ) newline

( whole string minus last character )
s 0 len 1 - substring . ( => abcdefg ) newline

( starting from a known character within the string and of m length )
s s 'b str-find dup m + substring . ( => bcd ) newline

( starting from a known substring within the string and of m length )
s s 'bc str-find dup m + substring . ( => bcd ) newline

Objeck

bundle Default {
  class SubString {
    function : Main(args : String[]) ~ Nil {
      s := "0123456789";

      n := 3;
      m := 4;
      c := '2';
      sub := "456";

      s->SubString(n, m)->PrintLine();
      s->SubString(n)->PrintLine();
      s->SubString(0, s->Size())->PrintLine();
      s->SubString(s->Find(c), m)->PrintLine();
      s->SubString(s->Find(sub), m)->PrintLine();
    }
  }
}

OCaml

From the interactive toplevel:

$ ocaml
# let s = "ABCDEFGH" ;;
val s : string = "ABCDEFGH"

# let n, m = 2, 3 ;;
val n : int = 2
val m : int = 3

# String.sub s n m ;;
- : string = "CDE"

# String.sub s n (String.length s - n) ;;
- : string = "CDEFGH"

# String.sub s 0 (String.length s - 1) ;;
- : string = "ABCDEFG"

# String.sub s (String.index s 'D') m ;;
- : string = "DEF"

# #load "str.cma";;
# let n = Str.search_forward (Str.regexp_string "DE") s 0 in
  String.sub s n m ;;
- : string = "DEF"

Oforth

: substrings(s, n, m)
   s sub(n, m) println
   s right(s size n - 1 +) println
   s left(s size 1 - ) println
   s sub(s indexOf('d'), m) println
   s sub(s indexOfAll("de"), m) println ;
Output:
"abcdefgh" 2 3 substrings
bcd
bcdefgh
abcdefg
def
def

OmniMark

  • There are several ways to achieve this, depending on the broader scenario, in OmniMark.
  • The solution, which follows, considers the individual substring 'challenges' using the same input string.
  • It uses groups, which are useful for restricting find, element, or other rules to certain streams.
  • The more common scenario is for substring patterns to be wanted within find or element rules (e.g., the string is found by a find rule and the substring is then matched with 'do scan {pattern}...match' or 'repeat scan {pattern}...match'.
  • Unicode handling, including beyond the BMP, is what's been illustrated in this example (e.g., 𝓞 is U+1D4DE). It could be simplified if it was certain only up to U+00FF characters are in the input; in that case, the macro would be unnecessary and the 'utf8-char' instances could be changed to 'any' or 'any-text'. (Both the OmniMark compiler and the OmniMark language itself operate at the byte level. They make no automatic interpretation of bytes into character numbers. OmniMark and character encodings That has benefits and drawbacks, but that's beyond the scope of this example.)
macro utf8-char is
   (["%16r{00}" to "%16r{7F}"] |
    ["%16r{C0}" to "%16r{DF}"] ["%16r{80}" to "%16r{BF}"] |
    ["%16r{E0}" to "%16r{EF}"] ["%16r{80}" to "%16r{BF}"] {2} |
    ["%16r{F0}" to "%16r{F7}"] ["%16r{80}" to "%16r{BF}"] {3}) macro-end

process
  local stream s initial {'This 𝓲𝓼 the 𝓞𝓶𝓷𝓲𝓜𝓪𝓻𝓴 solution.'}
  using group StartingFrom_n_CharactersInAndOf_m_Length submit s
  using group StartingFrom_n_charactersInUpToTheEndOfTheString submit s
  using group WholeStringMinusTheLastCharacter submit s
  using group StartingFromKnownCharacterAndOf_m_Length submit s
  using group StartingFromKnownSubstringAndOf_m_Length submit s

group StartingFrom_n_CharactersInAndOf_m_Length
  find value-start utf8-char{12} utf8-char{8} => p
    output p || '%n'  ; outputs characters 13 to 20: 𝓞𝓶𝓷𝓲𝓜𝓪𝓻𝓴

group StartingFrom_n_charactersInUpToTheEndOfTheString
  find value-start utf8-char{12} utf8-char+ => p
    output p || '%n' ; outputs characters 13 to last: 𝓞𝓶𝓷𝓲𝓜𝓪𝓻𝓴 solution.

group WholeStringMinusTheLastCharacter
  find value-start  ((lookahead not (utf8-char value-end)) utf8-char)+ => p
    output p || '%n' ; outputs characters 1 to (last - 1), so without the .

group StartingFromKnownCharacterAndOf_m_Length
  find 'T' utf8-char{3} => p
    output p || '%n' ; outputs his following T

group StartingFromKnownSubstringAndOf_m_Length
  find '𝓞𝓶𝓷𝓲𝓜' utf8-char{3} => p
    output p || '%n' ; outputs 𝓪𝓻𝓴 following 𝓞𝓶𝓷𝓲𝓜

group #implied
  find utf8-char
    ; ensures no other characters go to the output
Output:
𝓞𝓶𝓷𝓲𝓜𝓪𝓻𝓴
𝓞𝓶𝓷𝓲𝓜𝓪𝓻𝓴 solution.
This 𝓲𝓼 the 𝓞𝓶𝓷𝓲𝓜𝓪𝓻𝓴 solution
his
𝓪𝓻𝓴

Oz

declare
  fun {DropUntil Xs Prefix}
     case Xs of nil then nil
     [] _|Xr then
        if {List.isPrefix Prefix Xs} then Xs
        else {DropUntil Xr Prefix}
        end
     end
  end

  Digits = "1234567890"
in
  {ForAll
   [{List.take {List.drop Digits 2} 3}     = "345"
    {List.drop Digits 2}                   = "34567890"
    {List.take Digits {Length Digits}-1}   = "123456789"
    {List.take {DropUntil Digits "4"} 3}   = "456"
    {List.take {DropUntil Digits "56"} 3}  = "567"
    {List.take {DropUntil Digits "31"} 3}  = ""
   ]
   System.showInfo}

PARI/GP

Works with: PARI/GP version 2.7.4 and above
\\ Returns the substring of string str specified by the start position s and length n.
\\ If n=0 then to the end of str.
\\ ssubstr() 3/5/16 aev
ssubstr(str,s=1,n=0)={
my(vt=Vecsmall(str),ve,vr,vtn=#str,n1);
if(vtn==0,return(""));
if(s<1||s>vtn,return(str));
n1=vtn-s+1; if(n==0,n=n1); if(n>n1,n=n1);
ve=vector(n,z,z-1+s); vr=vecextract(vt,ve); return(Strchr(vr));
}

{\\ TEST
my(s="ABCDEFG",ns=#s);
print(" *** Testing ssubstr():");
print("1.",ssubstr(s,2,3));
print("2.",ssubstr(s));
print("3.",ssubstr(s,,ns-1));
print("4.",ssubstr(s,2));
print("5.",ssubstr(s,,4));
print("6.",ssubstr(s,0,4));
print("7.",ssubstr(s,3,7));
print("8.|",ssubstr("",1,4),"|");
}
Output:
 *** Testing ssubstr():
1.BCD
2.ABCDEFG
3.ABCDEF
4.BCDEFG
5.ABCD
6.ABCDEFG
7.CDEFG
8.||

Pascal

See also Delphi and Free Pascal

Works with: Extended Pascal

Remember, in Extended Pascal (ISO standard 10206), string(…) variables’ indices are 1‑based. Pay attention to the constraints below.

program substring(output);
var
	sample: string(20) value 'Foobar';
	n, m: integer value 1;
begin
	{ starting from n characters in and of m length - - - - - - - - - - - - - - - }
	writeLn(subStr(sample, n, m));
	writeLn(subStr(sample, n):m);
	writeLn(sample[n .. n + m - 1]);
	
	{ starting from n characters in, up to the end of the string  - - - - - - - - }
	writeLn(subStr(sample, n));
	writeLn(sample[n .. length(sample)]);
	
	{ whole string minus the last character - - - - - - - - - - - - - - - - - - - }
	writeLn(subStr(sample, 1, length(sample) - 1));
	writeLn(sample[1 .. pred(length(sample))]);
	writeLn(sample:length(sample) - 1);
	{ To make this a permanent change you can use
	    writeStr(sample, sample:pred(length(sample)); }
	
	{ starting from a known character within the string and of m length - - - - - }
	writeLn(subStr(sample, index(sample, 'b'), m));
	writeLn(subStr(sample, index(sample, 'b')):m);
	writeLn(sample[index(sample, 'b') .. index(sample, 'b') + m - 1]);
	
	{ starting from a known substring within the string and of m length - - - - - }
	writeLn(subStr(sample, index(sample, 'bar'), m));
	writeLn(subStr(sample, index(sample, 'bar')):m);
	writeLn(sample[index(sample, 'bar') .. index(sample, 'bar') + m - 1]);
end.
  • If a string(…) variable is designated bindable, for instance
    var myBindableStringVariable: bindable string(20);
    
    then it is not possible to use the array-like substring notation: That means
    myBindableStringVariable[firstCharacterIndex .. lastCharacterIndex]
    
    is not permitted since myBindableStringVariable is bindable.
  • It is mandatory that in sample[firstCharacterIndex .. lastCharacterIndex] both firstCharacterIndex and lastCharacterIndex are non-descending and denote valid indices in sample. That means both need to be in the range 1 .. length(sample). However, for an empty string this range would be empty. Therefore, the array-like substring notation cannot be used for an empty string.
  • In subStr(sample, firstCharacterIndex, substringLength) the substringLength has to be a non-negative integer less than or equal to length(sample). However, firstCharacterIndex + substringLength ‑ 1 may not exceed length(sample). Therefore, if sample is an empty string, the only permissible firstCharacterIndex value is 1 (positive one) and the only permissible substringLength is 0 (zero). Needless to say how pointless subStr('', 1, 0) is.
  • Furthermore, the totalWidth specification in write(myStringOrCharValue:totalWidth) (and writeLn/writeStr respectively) has to be greater than or equal to zero. To take advantage of this procedure in a fool-proof manner, you need to extend your width expression like this:
    write(sample:pred(length(sample), ord(length(sample) > 0))); { all but last char }
    

PascalABC.NET

{$zerobasedstrings}
const 
  n = 3;
  m = 2;

begin
  var s := '0123456789';
  Writeln(s.Substring(n, m));
  Writeln(s[n:]);
  Writeln(s[:^1]);
  Writeln(s.Substring(s.IndexOf('3'), m));
  Writeln(s.Substring(s.IndexOf('456'), m));
end.
Output:
34
3456789
012345678
34
45


Perl

my $str = 'abcdefgh';
print substr($str, 2, 3), "\n"; # Returns 'cde'
print substr($str, 2), "\n"; # Returns 'cdefgh'
print substr($str, 0, -1), "\n"; #Returns 'abcdefg'
print substr($str, index($str, 'd'), 3), "\n"; # Returns 'def'
print substr($str, index($str, 'de'), 3), "\n"; # Returns 'def'

Phix

Library: Phix/basics
--(1) starting from n characters in and of m length; 
--(2) starting from n characters in, up to the end of the string; 
--(3) whole string minus last character; 
--(4) starting from a known character within the string and of m length; 
--(5) starting from a known substring within the string and of m length. 
 
constant sentence = "the last thing the man said was the",
         n = 10, m = 5
integer k, l
l = n+m-1
if l<=length(sentence) then
    ?sentence[n..l]           -- (1)
end if
if n<=length(sentence) then
    ?sentence[n..-1]          -- (2) or [n..$]
end if
if length(sentence)>0 then
    ?sentence[1..-2]          -- (3) or [1..$-1]
end if
k = find('m',sentence)
l = k+m-1
if l<=length(sentence) then
    ?sentence[k..l]           -- (4)
end if
k = match("aid",sentence)
l = k+m-1
if l<=length(sentence) then
    ?sentence[k..l]           -- (5)
end if
Output:
"thing"
"thing the man said was the"
"the last thing the man said was th"
"man s"
"aid w"

Alternative version with no error handling, for those in a hurry (same ouput):

?sentence[n..n+m-1]
?sentence[n..-1]
?sentence[1..-2]
?(sentence[find('m',sentence)..$])[1..m]
?(sentence[match("aid",sentence)..$])[1..m]

If sentence is UTF-8 or UTF-16, you should explicitly use sequence utf32 = utf8_to_utf32(string utf8) or sequence utf32 = utf16_to_utf32(sequence utf16) before any slicing or find()/match(), and string utf8 = utf32_to_utf8(sequence utf32) or sequence utf16 = utf32_to_utf16(sequence utf32) before display. Note that unicode does not normally display correctly on a standard Windows console, but is fine in a GUI or Linux console or a web browser.

Phixmonti

include ..\Utilitys.pmt

/#
--(1) starting from n characters in and of m length; 
--(2) starting from n characters in, up to the end of the string; 
--(3) whole string minus last character; 
--(4) starting from a known character within the string and of m length; 
--(5) starting from a known substring within the string and of m length. 
#/

def myslice
    rot len var _|long
    rot rot
    over _|long swap - 1 +
    min   
    slice
enddef

"the last thing the man said was the"
10 var n 5 var m

n m myslice ?   /# (1) #/
len n swap myslice ?    /# (2) #/
dup -1 del ? /# (3) #/
'm' find m myslice ? /# (4) #/
"aid" find m myslice ? /# (5) #/

PHP

<?php
$str = 'abcdefgh';
$n = 2;
$m = 3;
echo substr($str, $n, $m), "\n"; //cde
echo substr($str, $n), "\n"; //cdefgh
echo substr($str, 0, -1), "\n"; //abcdefg
echo substr($str, strpos($str, 'd'), $m), "\n"; //def
echo substr($str, strpos($str, 'de'), $m), "\n"; //def
?>

Picat

go =>
  S = "Picat is fun",
  N = 3,
  M = 4,
  C = 'i', % must be a char
  SS = "is",
  test(S,N,M,C,SS).

test(S,N,M,C,SS) =>
  println($test(S,N,M,C,SS)),

  % - starting from n characters in and of m length;
  println(1=slice(S,N,N+M)),
  println(1=S[N..N+M]),  

  % - starting from n characters in, up to the end of the string;
  println(2=S.slice(N)),

  % - whole string minus last character;
  println(3=but_last(S)),
  println(3=S[1..S.len-1]),  

  % - starting from a known character within the string and of m length;
  println(4=substring4(S,C)),

  % - starting from a known substring within the string and of m length. 
  println(5=substring5(S,SS,M)),
  nl.
  
but_last(S) = slice(S,1,S.length-1).

substring4(S,C) = slice(S,S.find_first_of(C)).

% find is non-deterministic, hence the once/1
substring5(S,SS,M) = slice(S,Start,Start+M) =>  
  once(find(S,SS,Start,_End)).
Output:
test(Picat is fun,3,4,i,is)
1 = cat i
1 = cat i
2 = cat is fun
3 = Picat is fu
3 = Picat is fu
4 = icat is fun
5 = is fu


PicoLisp

(let Str (chop "This is a string")
   (prinl (head 4 (nth Str 6)))        # From 6 of 4 length
   (prinl (nth Str 6))                 # From 6 up to the end
   (prinl (head -1 Str))               # Minus last character
   (prinl (head 8 (member "s" Str)))   # From character "s" of length 8
   (prinl                              # From "isa" of length 8
      (head 8
         (seek '((S) (pre? "is a" S)) Str) ) ) )
Output:
is a
is a string
This is a strin
s is a s
is a str

PL/I

s='abcdefghijk';
n=4; m=3;
u=substr(s,n,m);
u=substr(s,n);
u=substr(s,1,length(s)-1);
u=left(s,length(s)-1);
u=substr(s,1,length(s)-1);
u=substr(s,index(s,'g'),m);

PowerShell

Since .NET and PowerShell use zero-based indexing, all character indexes have to be reduced by one.

# test string
$s = "abcdefgh"
# test parameters
$n, $m, $c, $s2 = 2, 3, [char]'d', $s2 = 'cd'

# starting from n characters in and of m length
# n = 2, m = 3
$s.Substring($n-1, $m)              # returns 'bcd'

# starting from n characters in, up to the end of the string
# n = 2
$s.Substring($n-1)                  # returns 'bcdefgh'

# whole string minus last character
$s.Substring(0, $s.Length - 1)      # returns 'abcdefg'

# starting from a known character within the string and of m length
# c = 'd', m =3
$s.Substring($s.IndexOf($c), $m)    # returns 'def'

# starting from a known substring within the string and of m length
# s2 = 'cd', m = 3
$s.Substring($s.IndexOf($s2), $m)   # returns 'cde'

Prolog

Works with: SWI Prolog version 7
substring_task(Str, N, M, Char, SubStr) :-
    sub_string(Str, N, M, _, Span),
    sub_string(Str, N, _, 0, ToEnd),
    sub_string(Str, 0, _, 1, MinusLast),
    string_from_substring_to_m(Str, Char, M, FromCharToMth),
    string_from_substring_to_m(Str, SubStr, M, FromSubToM),
    maplist( writeln,
            [ 'from n to m ':Span,
              'from n to end ': ToEnd,
              'string minus last char ': MinusLast,
              'form known char to m ': FromCharToMth,
              'from known substring to m ': FromSubToM ]).


string_from_substring_to_m(String, Sub, M, FromSubToM) :-
    sub_string(String, Before, _, _, Sub),
    sub_string(String, Before, M, _, FromSubToM).

Running it:

?- substring_task("abcdefghijk", 2, 4, "d", "ef").
from n to m :cdef
from n to end :cdefghijk
string minus last char :abcdefghij
form known char to m :defg
from known substring to m :efgh
true

Python

Python uses zero-based indexing, so the n'th character is at index n-1.

>>> s = 'abcdefgh'
>>> n, m, char, chars = 2, 3, 'd', 'cd'
>>> # starting from n=2 characters in and m=3 in length;
>>> s[n-1:n+m-1]
'bcd'
>>> # starting from n characters in, up to the end of the string;
>>> s[n-1:]
'bcdefgh'
>>> # whole string minus last character;
>>> s[:-1]
'abcdefg'
>>> # starting from a known character char="d" within the string and of m length;
>>> indx = s.index(char)
>>> s[indx:indx+m]
'def'
>>> # starting from a known substring chars="cd" within the string and of m length. 
>>> indx = s.index(chars)
>>> s[indx:indx+m]
'cde'
>>>

Quackery

find$ is defined at Count occurrences of a substring#Quackery.

  [ $ "abcdefgh" ] is s  ( --> $ )
  [ 2 ]            is n  ( --> n )
  [ 3 ]            is m  ( --> n )
  [ char d ]       is ch ( --> c )
  [ $ "cd" ]       is ss ( --> $ )

  s n split nip m split drop echo$ cr
  s n split nip echo$ cr
  s -1 split drop echo$ cr
  ch s tuck find split nip m split drop echo$ cr
  ss s tuck find$ split nip m split drop echo$ cr
Output:
cde
cdefgh
abcdefg
def
cde

R

s <- "abcdefgh"
n <- 2; m <- 2; char <- 'd'; chars <- 'cd'
substring(s, n, n + m)
substring(s, n)
substring(s, 1, nchar(s)-1)
indx <- which(strsplit(s, '')[[1]] %in% strsplit(char, '')[[1]])
substring(s, indx, indx + m)
indx <- which(strsplit(s, '')[[1]] %in% strsplit(chars, '')[[1]])[1]
substring(s, indx, indx + m)

Racket

#lang racket

(define str "abcdefghijklmnopqrstuvwxyz")

(define n 10)
(define m 2)
(define start-char #\x)
(define start-str "xy")

;; starting from n characters in and of m length;
(substring str n (+ n m)) ; -> "kl"

;; starting from n characters in, up to the end of the string;
(substring str m) ; -> "klmnopqrstuvwxyz"

;; whole string minus last character;
(substring str 0 (sub1 (string-length str))) ; -> "abcdefghijklmnopqrstuvwxy"

;; starting from a known character within the string and of m length;
(substring str (caar (regexp-match-positions (regexp-quote (string start-char))
                                             str))) ; -> "xyz"

;; starting from a known substring within the string and of m length.
(substring str (caar (regexp-match-positions (regexp-quote start-str)
                                             str))) ; -> "xyz"

Raku

(formerly Perl 6)

my $str = 'abcdefgh';
my $n = 2;
my $m = 3;
say $str.substr($n, $m);
say $str.substr($n);
say $str.substr(0, *-1);
say $str.substr($str.index('d'), $m);
say $str.substr($str.index('de'), $m);

Raven

define println use $s
   $s print "\n" print

"0123456789" as $str

$str 3 2 extract println      # at 4th pos get 2 chars
$str 8 4 extract println      # at 9th pos get 4 chars (when only 1 char available)


$str 3  $str length  extract println      # at 4th pos get all chars to end of str
$str 3  0x7FFFFFFF  extract println      # at 4th pos get all chars to end of str

$str 3 -1 extract println      # at 4th pos get rest of chars but last one
$str 0 -1 extract println      # all chars but last one

"3" as $matchChr               # starting chr for extraction
4 as $subLen                   # Nr chars after found starting char
$str $matchChr split as $l    
"" $l 0 set     $l $matchChr join 
0 $subLen extract println

"345" as $matchChrs            # starting chrs for extraction
6 as $subLen                   # Nr chars after found starting chars
$str $matchChrs split as $l    
"" $l 0 set     $l $matchChrs join 
0 $subLen extract println
Output:
34
89
3456789
3456789
345678
012345678
3456
345678

REBOL

REBOL [
	Title: "Retrieve Substring"
	URL: http://rosettacode.org/wiki/Substring#REBOL
]

s: "abcdefgh"  n: 2  m: 3  char: #"d"  chars: "cd"

; Note that REBOL uses base-1 indexing. Strings are series values,
; just like blocks or lists so I can use the same words to manipulate
; them. All these examples use the 'copy' function against the 's'
; string with a particular offset as needed.  

; For the fragment "copy/part  skip s n - 1  m", read from right to
; left.  First you have 'm', which we ignore for now. Then evaluate
; 'n - 1' (makes 1), to adjust the offset. Then 'skip' jumps from the
; start of the string by that offset. 'copy' starts copying from the
; new start position and the '/part' refinement limits the copy by 'm'
; characters. 

print ["Starting from n, length m:"  
	copy/part  skip s n - 1  m]

; It may be helpful to see the expression with optional parenthesis:

print ["Starting from n, length m (parens):"  
	(copy/part  (skip s (n - 1))  m)]

; This example is much simpler, so hopefully it's easier to see how
; the string start is position for the copy:

print ["Starting from n to end of string:" 
	copy skip s n - 1]

print ["Whole string minus last character:" 
	copy/part s (length? s) - 1]

print ["Starting from known character, length m:"
	copy/part  find s char  m]

print ["Starting from substring, length m:"
	copy/part  find s chars  m]
Output:
Script: "Retrieve Substring" (6-Dec-2009)
Starting from n, length m: bcd
Starting from n, length m (parens): bcd
Starting from n to end of string: bcdefgh
Whole string minus last character: abcdefg
Starting from known character, length m: def
Starting from substring, length m: cde

ReScript

let s = "ABCDEFGH"
let from = 2
let length = 3

Js.log2("Original string: ", s)

Js.log(Js.String.substrAtMost(~from, ~length, s))
Js.log(Js.String.substr(~from, s))
Js.log(Js.String.substrAtMost(~from=0, ~length=(Js.String2.length(s) - 1), s))

Js.log(Js.String.substrAtMost(~from=(Js.String.indexOf("B", s)), ~length, s))
Js.log(Js.String.substrAtMost(~from=(Js.String.indexOf("BC", s)), ~length, s))
Output:
$ bsc substr.res > substr.js
$ node substr.js

Original string: ABCDEFGH

CDE
CDEFGH
ABCDEFG
BCD
BCD

REXX

Note:   in REXX,   the 1st character   index   of a string is   1,   not   0.

/*REXX program demonstrates various ways to extract substrings from a  string  of characters.*/
$='abcdefghijk';  n=4;  m=3        /*define some constants: string, index, length of string. */
say 'original string='$            /* [↑]   M   can be zero  (which indicates a null string).*/
L=length($)                        /*the length of the  $  string   (in bytes or characters).*/
              say center(1,30,'═') /*show a centered title for the  1st  task requirement.   */
u=substr($, n, m)                  /*start from  N  characters in  and of  M  length.        */
say u
parse var $ =(n) a +(m)            /*an alternate method by using the  PARSE  instruction.   */
say a
              say center(2,30,'═') /*show a centered title for the  2nd  task requirement.   */
u=substr($,n)                      /*start from  N  characters in,  up to the end-of-string. */
say u
parse var $ =(n) a                 /*an alternate method by using the  PARSE  instruction.   */
say a
              say center(3,30,'═') /*show a centered title for the  3rd  task requirement.   */
u=substr($, 1, L-1)                /*OK:     the entire string  except  the last character.  */
say u
v=substr($, 1, max(0, L-1) )       /*better: this version handles the case of a null string. */
say v
lm=L-1
parse var $ a +(lm)                /*an alternate method by using the  PARSE  instruction.   */
say a
              say center(4,30,'═') /*show a centered title for the  4th  task requirement.   */
u=substr($,pos('g',$), m)          /*start from a known char within the string of length  M. */
say u
parse var $ 'g' a +(m)             /*an alternate method by using the  PARSE  instruction.   */
say a
              say center(5,30,'═') /*show a centered title for the  5th  task requirement.   */
u=substr($,pos('def',$),m)         /*start from a known substr within the string of length M.*/
say u
parse var $ 'def' a +(m)           /*an alternate method by using the  PARSE  instruction.   */
say a                              /*stick a fork in it, we're all done and Bob's your uncle.*/

output   when using the (internal) default strings:

original string=abcdefghijk
══════════════1═══════════════
def
def
══════════════2═══════════════
defghijk
defghijk
══════════════3═══════════════
abcdefghij
abcdefghij
abcdefghij
══════════════4═══════════════
ghi
ghi
══════════════5═══════════════
def
def

Programming note:   generally, the REXX   parse   statement is faster than using an assignment statement and using a BIF (built-in function), but the use of   parse   is more obtuse to novice programmers.

Ring

cStr = "a":"h"  # 'abcdefgh'
n = 3  m = 3
# starting from n characters in and of m length
See substr(cStr,n, m) + nl          #=> cde
# starting from n characters in, up to the end of the string
See substr(cStr,n) + nl             #=> cdefgh
# whole string minus last character
See substr(cstr,1,len(cStr)-1) + nl #=> abcdefg
# starting from a known character within the string and of m length
See substr(cStr,substr(cStr,"e"),m) +nl #=> efg
# starting from a known substring within the string and of m length
See substr(cStr,substr(cStr,"de"),m) +nl #=> def

RPG

      *                                         1...5....1....5....2....5..    
     D myString        S             30    inz('Liebe bewegt das Universum!')  
     D output          S             30    inz('')                             
     D n               S              2  0 inz(1)                              
     D m               S              2  0 inz(5)                              
     D length          S              2  0 inz(0)                              
     D find            S              2  0 inz(0)                              
                                                                               
      /free                                                                    
       *inlr = *on;                                                           
        dsply    %subst(myString:n:m);                   
        dsply    %subst(myString:7:20);                  
                                                         
        length = %len(%trim(myString));                  
        dsply    %subst(myString:1:length-1);            
                                                         
        find   = %scan('U':myString);                    
        dsply    %subst(myString:find:9);                
                                                         
        find   = %scan('bewegt':myString);               
        dsply    %subst(myString:find:%len('bewegt'));   
                                                         
        output = ' *** end *** ';                        
        dsply ' ' ' ' output;                            
      /end-free
Output:
DSPLY  Liebe                     
DSPLY  bewegt das Universum      
DSPLY  Liebe bewegt das Universum
DSPLY  Universum                 
DSPLY  bewegt                                   

RPL

Works with: Halcyon Calc version 4.2.7
Code Comments
≪  → string n m char sub ≪ 
   string n DUP m + 1 - SUB
   string n OVER SIZE SUB
   string 1 OVER SIZE 1 - SUB
   string DUP char POS DUP m + 1 - SUB
   string DUP sub  POS DUP m + 1 - SUB
≫ ≫ SHOWC STO
( string start length char sub -- sub1 .. sub5 )
 from n characters in and of m length
 from n characters in, up to the end of the string
 whole string minus the last character
 from a character within the string and of m length
 from a substring within the string and of m length

The following piece of code will deliver what is required:

"abcdefgh" 2 3 "d" "cd" SHOWC
Output:
5: bcd
4: bcdefgh
3: abcdefg
2: def
1: cde

Ruby

str = 'abcdefgh'
n = 2
m = 3
puts str[n, m]                  #=> cde
puts str[n..m]                  #=> cd
puts str[n..-1]                 #=> cdefgh
puts str[0..-2]                 #=> abcdefg
puts str[str.index('d'), m]     #=> def
puts str[str.index('de'), m]    #=> def
puts str[/a.*d/]                #=> abcd

Rust

let s = "abc文字化けdef";
let n = 2;
let m = 3;

    // Print 3 characters starting at index 2 (c文字)
println!("{}", s.chars().skip(n).take(m).collect::<String>());

    // Print all characters starting at index 2 (c文字化けdef)
println!("{}", s.chars().skip(n).collect::<String>());

    // Print all characters except the last (abc文字化けde)
println!("{}", s.chars().rev().skip(1).collect::<String>());

    // Print 3 characters starting with 'b' (bc文)
let cpos = s.find('b').unwrap();
println!("{}", s[cpos..].chars().take(m).collect::<String>());

    // Print 3 characters starting with "けd" (けde)
let spos = s.find("けd").unwrap();
println!("{}", s[spos..].chars().take(m).collect::<String>());

SAS

data _null_;
   a="abracadabra";
   b=substr(a,2,3); /* first number is position, starting at 1,
                       second number is length */
   put _all_;
run;

Sather

class MAIN is
  main is
    s ::= "hello world shortest program";
    #OUT + s.substring(12, 5) + "\n";
    #OUT + s.substring(6) + "\n";
    #OUT + s.head( s.size - 1) + "\n";
    #OUT + s.substring(s.search('w'), 5) + "\n";
    #OUT + s.substring(s.search("ro"), 3) + "\n";
  end;
end;

Scala

Library: Scala
object Substring {
  // Ruler             1         2         3         4         5         6
  //         012345678901234567890123456789012345678901234567890123456789012
  val str = "The good life is one inspired by love and guided by knowledge."
  val (n, m) = (21, 16) // An one-liner to set n = 21, m = 16

  // Starting from n characters in and of m length
  assert("inspired by love" == str.slice(n, n + m))
  
  // Starting from n characters in, up to the end of the string
  assert("inspired by love and guided by knowledge." == str.drop(n))
  
  // Whole string minus last character
  assert("The good life is one inspired by love and guided by knowledge" == str.init)
  
  // Starting from a known character within the string and of m length
  assert("life is one insp" == str.dropWhile(_ != 'l').take(m) )
  
  // Starting from a known substring within the string and of m length
  assert("good life is one" == { val i = str.indexOf("good"); str.slice(i, i + m) })
  // Alternatively
  assert("good life is one" == str.drop(str.indexOf("good")).take(m))
}

Scheme

Works with: Guile
(define s "Hello, world!")
(define n 5)
(define m (+ n 6))

(display (substring s n m))
(newline)

(display (substring s n))
(newline)

(display (substring s 0 (- (string-length s) 1)))
(newline)

(display (substring s (string-index s #\o) m))
(newline)

(display (substring s (string-contains s "lo") m))
(newline)

Sed

# 2 chars starting from 3rd
$ echo string | sed -r 's/.{3}(.{2}).*/\1/'
in
# remove first 3 chars
echo string | sed -r 's/^.{3}//'
# delete last char
$ echo string | sed -r 's/.$//'
strin
# `r' with two following chars
$ echo string | sed -r 's/.*(r.{2}).*/\1/'
rin

Seed7

$ include "seed7_05.s7i";

const proc: main is func
  local
    const string: stri is "abcdefgh";
    const integer: N is 2;
    const integer: M is 3;
  begin
    writeln(stri[N len M]);
    writeln(stri[N ..]);
    writeln(stri[.. pred(length(stri))]);
    writeln(stri[pos(stri, 'c') len M]);
    writeln(stri[pos(stri, "de") len M]);
  end func;
Output:
bcd
bcdefgh
abcdefg
cde
def

SenseTalk

Note: SenseTalk indexes from 1 and ranges are inclusive

set mainString to "87654321"
set n to 3
set m to 4
set c to "5"
set sub to "654"

put characters n + 1 to  n + m of mainString

put characters  n + 1 to end of mainString

put characters first to penultimate of mainString

set characterOffset to offset of c in mainString
put characters characterOffset to characterOffset + m - 1 of mainString

set subOffset to offset of sub in mainString
put characters subOffset to subOffset + m - 1 of mainString

Sidef

var str = 'abcdefgh';
var n = 2;
var m = 3;
say str.substr(n, m);                   #=> cde
say str.substr(n);                      #=> cdefgh
say str.substr(0, -1);                  #=> abcdefg
say str.substr(str.index('d'), m);      #=> def
say str.substr(str.index('de'), m);     #=> def

Slate

#s := 'hello world shortest program'.
#n := 13.
#m := 4.
inform: (s copyFrom: n to: n + m).
inform: (s copyFrom: n).
inform: s allButLast.
inform: (s copyFrom: (s indexOf: $w) to: (s indexOf: $w) + m).
inform: (s copyFrom: (s indexOfSubSeq: 'ro') to: (s indexOfSubSeq: 'ro') + m).

Smalltalk

The distinction between searching a single character or a string into another string is rather blurred. In the following code, instead of using 'w' (a string) we could use $w (a character), but it makes no difference.

|s|
s := 'hello world shortest program'.

(s copyFrom: 13 to: (13+4)) displayNl.
"4 is the length (5) - 1, since we need the index of the
 last char we want, which is included" 

(s copyFrom: 7) displayNl.
(s allButLast) displayNl.

(s copyFrom: ((s indexOfRegex: 'w') first) 
   to: ( ((s indexOfRegex: 'w') first) + 4) ) displayNl.
(s copyFrom: ((s indexOfRegex: 'ro') first)
   to: ( ((s indexOfRegex: 'ro') first) + 2) ) displayNl.

These last two examples in particular seem rather complex, so we can extend the string class.

Works with: GNU Smalltalk
String extend [
  copyFrom: index length: nChar [
    ^ self copyFrom: index to: ( index + nChar - 1 )
  ]
  copyFromRegex: regEx length: nChar [
    |i|
    i := self indexOfRegex: regEx.
    ^ self copyFrom: (i first) length: nChar
  ]
].

"and show it simpler..."

(s copyFrom: 13 length: 5) displayNl.
(s copyFromRegex: 'w' length: 5) displayNl.
(s copyFromRegex: 'ro' length: 3) displayNl.

SNOBOL4

	string = "abcdefghijklmnopqrstuvwxyz"
	n = 12
	m = 5
	known_char = "q"
	known_str = "pq"
*  starting from n characters in and of m length;
	string len(n - 1) len(m) . output	
* starting from n characters in, up to the end of the string;
	string len(n - 1) rem . output
* whole string minus last character;
	string rtab(1) . output
* starting from a known character within the string and of m length;
	string break(known_char) len(m) . output
* starting from a known substring <= m within the string and of m length. 
	string (known_str len(m - size(known_str))) . output
end
Output:
 lmnop
 lmnopqrstuvwxyz
 abcdefghijklmnopqrstuvwxy
 qrstu
 pqrst

SQL PL

Works with: Db2 LUW

In Db2, there are different ways to find the position of a character or substring. For this reason, several examples are shown. Please take a look at the documentation for more details.

select 'the quick brown fox jumps over the lazy dog' from sysibm.sysdummy1;
select substr('the quick brown fox jumps over the lazy dog', 5, 15) from sysibm.sysdummy1;
select substr('the quick brown fox jumps over the lazy dog', 32) from sysibm.sysdummy1;
select substr('the quick brown fox jumps over the lazy dog', 1, length ('the quick brown fox jumps over the lazy dog') - 1) from sysibm.sysdummy1;

select locate('j', 'the quick brown fox jumps over the lazy dog') from sysibm.sysdummy1;
select locate_in_string('the quick brown fox jumps over the lazy dog', 'j') from sysibm.sysdummy1;
select posstr('the quick brown fox jumps over the lazy dog', 'j') from sysibm.sysdummy1;
select position('j', 'the quick brown fox jumps over the lazy dog',  OCTETS) from sysibm.sysdummy1;

select substr('the quick brown fox jumps over the lazy dog', locate('j', 'the quick brown fox jumps over the lazy dog')) from sysibm.sysdummy1;

select locate('fox', 'the quick brown fox jumps over the lazy dog') from sysibm.sysdummy1;
select locate_in_string('the quick brown fox jumps over the lazy dog', 'fox') from sysibm.sysdummy1;
select posstr('the quick brown fox jumps over the lazy dog', 'fox') from sysibm.sysdummy1;
select position('fox', 'the quick brown fox jumps over the lazy dog',  OCTETS) from sysibm.sysdummy1;

select substr('the quick brown fox jumps over the lazy dog', locate('fox', 'the quick brown fox jumps over the lazy dog')) from sysibm.sysdummy1;

Output:

db2 => select 'the quick brown fox jumps over the lazy dog' from sysibm.sysdummy1;
1                                          
-------------------------------------------
the quick brown fox jumps over the lazy dog

  1 record(s) selected.
db2 => select substr('the quick brown fox jumps over the lazy dog', 5, 15) from sysibm.sysdummy1;
1              
---------------
quick brown fox

  1 record(s) selected.

db2 => select substr('the quick brown fox jumps over the lazy dog', 32) from sysibm.sysdummy1;
1                                          
-------------------------------------------
the lazy dog                               

  1 record(s) selected.

db2 => select substr('the quick brown fox jumps over the lazy dog', 1, length ('the quick brown fox jumps over the lazy dog') - 1) from sysibm.sysdummy1;
1                                          
-------------------------------------------
the quick brown fox jumps over the lazy do 

  1 record(s) selected.


db2 => select substr('the quick brown fox jumps over the lazy dog', locate('j', 'the quick brown fox jumps over the lazy dog')) from sysibm.sysdummy1;

1                                          
-------------------------------------------
jumps over the lazy dog                    

  1 record(s) selected.

db2 => select substr('the quick brown fox jumps over the lazy dog', locate('fox', 'the quick brown fox jumps over the lazy dog')) from sysibm.sysdummy1;

1                                          
-------------------------------------------
fox jumps over the lazy dog                

  1 record(s) selected.

Stata

s = "Ἐν ἀρχῇ ἐποίησεν ὁ θεὸς τὸν οὐρανὸν καὶ τὴν γῆν"

usubstr(s, 25, 11)
  τὸν οὐρανὸν

usubstr(s, 25, .)
  τὸν οὐρανὸν καὶ τὴν γῆν

usubstr(s, 1, ustrlen(s)-1)
  Ἐν ἀρχῇ ἐποίησεν ὁ θεὸς τὸν οὐρανὸν καὶ τὴν γῆ

usubstr(s, -3, .)
  γῆν

Swift

let string = "Hello, Swift language"
let (n, m) = (5, 4)

// Starting from `n` characters in and of `m` length.
do {
  let start = string.startIndex.advancedBy(n)
  let end = start.advancedBy(m)
  // Pure-Swift (standard library only):
  _ = string[start..<end]
  // With Apple's Foundation framework extensions:
  string.substringWithRange(start..<end)
}

// Starting from `n` characters in, up to the end of the string.
do {
  // Pure-Swift (standard library only):
  _ = String(
    string.characters.suffix(string.characters.count - n)
  )
  // With Apple's Foundation framework extensions:
  _ = string.substringFromIndex(string.startIndex.advancedBy(n))
}

// Whole string minus last character.
do {
  // Pure-Swift (standard library only):
  _ = String(
    string.characters.prefix(
      string.characters.count.predecessor()
    )
  )
  // With Apple's Foundation framework extensions:
  _ = string.substringToIndex(string.endIndex.predecessor())
}

// Starting from a known character within the string and of `m` length.
do {
  // Pure-Swift (standard library only):
  let character = Character("l")
  guard let characterIndex = string.characters.indexOf(character) else {
    fatalError("Index of '\(character)' character not found.")
  }
  let endIndex = characterIndex.advancedBy(m)
  _ = string[characterIndex..<endIndex]
}

// Starting from a known substring within the string and of `m` length.
do {
  // With Apple's Foundation framework extensions:
  let substring = "Swift"
  guard let range = string.rangeOfString(substring) else {
    fatalError("Range of substring \(substring) not found")
  }
  let start = range.startIndex
  let end = start.advancedBy(m)
  string[start..<end]
}

Tailspin

Tailspin doesn't really let you manipulate parts of strings. You can get a list of characters (or, really, clumps of combining characters) by

[$s...]

and manipulate parts of that list, and recombine as

'$a...;'

if you really want to. The better Tailspin way to handle parts of strings is to use a "composer" to compose meaningful structure from the string (and discard unwanted parts).

composer substr&{from:, length:}
  (<'.{$:$from-1;}'>) <'.{$length;}'> (<'.*'>)
end substr

'abcdef' -> substr&{from:3, length:2} -> !OUT::write
'
' -> !OUT::write

composer substrFrom&{from:}
  (<'.{$:$from-1;}'>) <'.*'>
end substrFrom

'abcdef' -> substrFrom&{from:4} -> !OUT::write
'
' -> !OUT::write

composer chopLast
  <'(.(?=.))*'> (<'.'>)
end chopLast

'abcdef' -> chopLast -> !OUT::write
'
' -> !OUT::write

composer substrStarting&{prefix:, length:}
  (<~='$prefix;'>) <'.{$length;}'> (<'.*'>)
end substrStarting

'abcdef' -> substrStarting&{prefix: 'b', length: 2} -> !OUT::write
'
' -> !OUT::write

'abcdef' -> substrStarting&{prefix: 'cd', length: 3} -> !OUT::write
'
' -> !OUT::write
Output:
cd
def
abcde
bc
cde

Tcl

set str "abcdefgh"
set n 2
set m 3

puts [string range $str $n [expr {$n+$m-1}]]
puts [string range $str $n end]
puts [string range $str 0 end-1]
# Because Tcl does substrings with a pair of indices, it is easier to express
# the last two parts of the task as a chained pair of [string range] operations.
# A maximally efficient solution would calculate the indices in full first.
puts [string range [string range $str [string first "d" $str] end] [expr {$m-1}]]
puts [string range [string range $str [string first "de" $str] end] [expr {$m-1}]]

# From Tcl 8.5 onwards, these can be contracted somewhat.
puts [string range [string range $str [string first "d" $str] end] $m-1]
puts [string range [string range $str [string first "de" $str] end] $m-1]

Of course, if you were doing 'position-plus-length' a lot, it would be easier to add another subcommand to string, like this:

Works with: Tcl version 8.5
# Define the substring operation, efficiently
proc ::substring {string start length} {
    string range $string $start [expr {$start + $length - 1}]
}
# Plumb it into the language
set ops [namespace ensemble configure string -map]
dict set ops substr ::substring
namespace ensemble configure string -map $ops

# Now show off by repeating the challenge!
set str "abcdefgh"
set n 2
set m 3

puts [string substr $str $n $m]
puts [string range $str $n end]
puts [string range $str 0 end-1]
puts [string substr $str [string first "d" $str] $m]
puts [string substr $str [string first "de" $str] $m]

TUSCRIPT

$$ MODE TUSCRIPT
string="abcdefgh", n=4,m=n+2
substring=EXTRACT (string,#n,#m)
  PRINT substring
substring=Extract (string,#n,0)
  PRINT substring
substring=EXTRACT (string,0,-1)
  PRINT substring
n=SEARCH (string,":d:"),m=n+2
substring=EXTRACT (string,#n,#m)
  PRINT substring
substring=EXTRACT (string,":{substring}:"|,0)
  PRINT substring
Output:
de
defgh
abcdefg
de
fgh

UNIX Shell

POSIX shells

Works with: Almquist Shell
str="abc qrdef qrghi"
n=6
m=3

expr "x$str" : "x.\{$n\}\(.\{1,$m\}\)"
expr "x$str" : "x.\{$n\}\(.*\)"
printf '%s\n' "${str%?}"
expr "r${str#*r}" : "\(.\{1,$m\}\)"
expr "qr${str#*qr}" : "\(.\{1,$m\}\)"
def
def qrghi
abc qrdef qrgh
rde
qrd

This program uses expr(1) to capture a substring.

Bourne Shell

Works with: Bourne Shell
str="abc qrdef qrghi"
n=6
m=3

expr "x$str" : "x.\{$n\}\(.\{1,$m\}\)"
expr "x$str" : "x.\{$n\}\(.*\)"
expr "x$str" : "x\(.*\)."

index() {
	i=0 s=$1
	until test "x$s" = x || expr "x$s" : "x$2" >/dev/null; do
		i=`expr $i + 1` s=`expr "x$s" : "x.\(.*\)"`
	done
	echo $i
}
expr "x$str" : "x.\{`index "$str" r`\}\(.\{1,$m\}\)"
expr "x$str" : "x.\{`index "$str" qr`\}\(.\{1,$m\}\)"
def
def qrghi
abc qrdef qrgh
rde
qrd

zsh

Works with: zsh

Note that the last two constructs won't work with bash as only zsh supports nested string manipulation.

#!/bin/zsh
string='abcdefghijk'
echo ${string:2:3}              # Display 3 chars starting 2 chars in ie: 'cde'
echo ${string:2}                # Starting 2 chars in, display to end of string
echo ${string:0:${#string}-1}   # Whole string minus last character
echo ${string%?}                 # Shorter variant of the above
echo ${${string/*c/c}:0:3}      # Display 3 chars starting with 'c'
echo ${${string/*cde/cde}:0:3}  # Display 3 chars starting with 'cde'

Pipe

This example shows how to cut(1) a substring from a string.

Translation of: AWK
Works with: Almquist Shell
#!/bin/sh
str=abcdefghijklmnopqrstuvwxyz
n=12
m=5

printf %s "$str" | cut -c $n-`expr $n + $m - 1`
printf %s "$str" | cut -c $n-
printf '%s\n' "${str%?}"
printf q%s "${str#*q}" | cut -c 1-$m
printf pq%s "${str#*pq}" | cut -c 1-$m
Output:
$ sh substring.sh                                                              
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
qrstu
pqrst
  • cut -c counts characters from 1.
  • cut(1) runs on each line of standard input, therefore the string must not contain a newline.
  • One can use the old style `expr $n + $m - 1` or the new style $((n + m - 1)) to calculate the index.
  • cut(1) prints the substring to standard output. To put the substring in a variable, use one of
    • var=`printf %s "$str" | cut -c $n-\`expr $n + $m - 1\``
    • var=$( printf %s "$str" | cut -c $n-$((n + m - 1)) )

Vala

string s = "Hello, world!";
int n = 1;
int m = 3;
// start at n and go m letters
string s_n_to_m = s[n:n+m];
// start at n and go to end
string s_n_to_end = s[n:s.length];
// start at beginning and show all but last
string s_notlast = s[0:s.length - 1];
// start from known letter and then go m letters
int index_of_l = s.index_of("l");
string s_froml_for_m = s[index_of_l:index_of_l + m];
// start from known substring then go m letters
int index_of_lo = s.index_of("lo");
string s_fromlo_for_m = s[index_of_lo:index_of_lo + m];

V (Vlang)

Translation of: AutoHotkey

1) Substring function argument in V (Vlang) uses end position versus length in AHK. 2) V (Vlang) arrays are 0 index based.

fn main() {
    str := "abcdefghijklmnopqrstuvwxyz"
    find_char := "q"
    find_string := "pq"
    n := 12
    m := 5
	
//  starting from n characters in and of m length
    println(str.substr(n - 1, (n - 1) + m))
	
//  starting from n characters in, up to the end of the string	
    println(str.substr(n - 1, str.len))
	
//  whole string minus last character		
    println(str.substr(0, str.len - 1))
	
//  starting from a known character within the string and of m length // returns nothing if not found	
    println(str.substr(str.index(find_char) or {return}, (str.index(find_char) or {return}) + m))
	
//  starting from a known character within the string and of m length // returns nothing if not found
    println(str.substr(str.index(find_string) or {return}, (str.index(find_string) or {return}) + m))
}
Output:
lmnop
lmnopqrstuvwxyz
abcdefghijklmnopqrstuvwxy
qrstu
pqrst

Wart

s <- "abcdefgh"
s.0
=> "a"

# starting from n characters in and of m length;
def (substr s start len)
  (s start start+len)
(substr s 3 2)
=> "de"

# starting from n characters in, up to the end of the string
(s 3 nil)
=> "defgh"

# whole string minus last character;
(s 3 -1)
=> "defg"

# starting from a known character within the string and of <tt>m</tt> length;
# starting from a known substring within the string and of <tt>m</tt> length.
let start (pos s pat)
  (s start start+m)

Wren

Translation of: Go
Library: Wren-str
import "./str" for Str
 
var s  = "αβγδεζηθ"
var n = 2
var m = 3
var kc = "δ"  // known character
var ks = "δε" // known string
// for reference
System.print("Index of characters:  01234567")
System.print("Complete string:      %(s)")
// starting from n characters in and of m length
System.print("Start %(n), length %(m):    %(Str.sub(s, n...n+m))")
// starting from n characters in, up to the end of the string
System.print("Start %(n), to end:      %(Str.sub(s, n..-1))")
// whole string minus last character
System.print("All but last:         %(Str.sub(s, 0..-2))")
// starting from a known character within the string and of m length
var dx = s.indexOf(kc)
if (dx >= 0) {
    System.print("Start '%(kc)', length %(m):  %(Str.sub(s[dx..-1], 0...m))")
}
// starting from a known substring within the string and of m length
var sx = s.indexOf(ks)
if (sx >= 0) {
    System.print("Start '%(ks)', length %(m): %(Str.sub(s[sx..-1], 0...m))")
}
Output:
Index of character:   01234567
Complete string:      αβγδεζηθ
Start 2, length 3:    γδε
Start 2, to end:      γδεζηθ
All but last:         αβγδεζη
Start 'δ', length 3:  δεζ
Start 'δε', length 3: δεζ

XPL0

include xpllib;         \provides StrLen and StrFind

proc PMid(S, N, M);     \Print string at Nth character M chars long
char S, N, M, I;
[for I:= 1 to M do ChOut(0, S(N-2+I));
CrLf(0);
];

char S;
def  N=2, M=3;
[S:= "abcdefgh";
PMid(S, N, M);                  \starting from N chars in and of M length
PMid(S, N, StrLen(S)-N+1);      \starting from N chars in, up to end of string
PMid(S, 1, StrLen(S)-1);        \whole string minus last character
PMid(StrFind(S, "d" ), 1, M);   \starting from known char and of M length
PMid(StrFind(S, "cd"), 1, M);   \starting from known substring and of M length
]
Output:
bcd
bcdefgh
abcdefg
def
cde

Yorick

str = "abcdefgh";
n = 2;
m = 3;

// starting from n character in and of m length
write, strpart(str, n:n+m-1);
// starting from n character in, up to the end of the string
write, strpart(str, n:);
// whole string minus last character
write, strpart(str, :-1);
// starting from a known character within the string and of m length
match = strfind("d", str);
write, strpart(str, [match(1), match(1)+m]);
// starting from a known substring within the string and of m length
match = strfind("cd", str);
write, strpart(str, [match(1), match(1)+m]);

zkl

8 bit ASCII

var str = "abcdefgh", n = 2, m = 3;
str[n,m]  //-->"cde"
str[n,*]  //-->"cdefgh"
str[0,-1] //-->"abcdefg"
str[str.find("d"),m]  //-->"def"
str[str.find("de"),m] //-->"def"