String prepend

From Rosetta Code
Task
String prepend
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

Create a string variable equal to any text value.

Prepend the string variable with another string literal.

If your language supports any idiomatic ways to do this without referring to the variable twice in one expression, include such solutions.


To illustrate the operation, show the content of the variable.

11l

Translation of: Python
V s = ‘12345678’
s = ‘0’s
print(s)
Output:
012345678

360 Assembly

*        String prepend - 14/04/2020
PREPEND  CSECT
         USING  PREPEND,13         base register
         B      72(15)             skip savearea
         DC     17F'0'             savearea
         SAVE   (14,12)            save previous context
         ST     13,4(15)           link backward
         ST     15,8(13)           link forward
         LR     13,15              set addressability
         MVC    C+L'B(L'A),A       c=a
         MVC    C(L'B),B           c=b+c  (prepend)
         XPRNT  C,L'C              print buffer
         L      13,4(0,13)         restore previous savearea pointer
         RETURN (14,12),RC=0       restore registers from calling sav
A        DC     C'world!'          a
B        DC     C'Hello '          b
C        DC     CL80' '            c
         END    PREPEND
Output:
Hello world!

AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits
/* ARM assembly AARCH64 Raspberry PI 3B */
/*  program appendstr64.s   */

/*******************************************/
/* Constantes file                         */
/*******************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc"

/*******************************************/
/* Initialized data                        */
/*******************************************/
.data
szMessString:            .asciz "British Museum.\n"
szComplement:            .skip 80
szStringStart:           .asciz "The rosetta stone is at "
szCarriageReturn:        .asciz "\n"
/*******************************************/
/* UnInitialized data                      */
/*******************************************/
.bss 
/*******************************************/
/*  code section                           */
/*******************************************/
.text
.global main 
main: 
 
    ldr x0,qAdrszMessString               // display message
    bl affichageMess

    ldr x0,qAdrszMessString
    ldr x1,qAdrszStringStart
    bl prepend                             // append sting2 to string1
    ldr x0,qAdrszMessString
    bl affichageMess

    ldr x0,qAdrszCarriageReturn
    bl affichageMess

 
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
qAdrszStringStart:        .quad szStringStart
qAdrszCarriageReturn:     .quad szCarriageReturn
/**************************************************/
/*     append two strings                         */ 
/**************************************************/
/* x0 contains the address of the string1 */
/* x1 contains the address of the string2 */
prepend:
    stp x1,lr,[sp,-16]!            // save  registers
    mov x3,#0                                // length counter 
1:                                           // compute length of string 1
    ldrb w4,[x0,x3]
    cmp w4,#0
    cinc  x3,x3,ne                           // increment to one if not equal
    bne 1b                                   // loop if not equal
    mov x5,#0                                // length counter insertion string
2:                                           // compute length of insertion string
    ldrb w4,[x1,x5]
    cmp x4,#0
    cinc  x5,x5,ne                           // increment to one if not equal
    bne 2b
    cmp x5,#0
    beq 99f                                  // string empty -> error
    add x3,x3,x5                             // add 2 length
    add x3,x3,#1                             // +1 for final zero
    mov x6,x0                                // save address string 1
    mov x0,#0                                // allocation place heap
    mov x8,BRK                               // call system 'brk'
    svc #0
    mov x5,x0                                // save address heap for output string
    add x0,x0,x3                             // reservation place x3 length
    mov x8,BRK                               // call system 'brk'
    svc #0
    cmp x0,#-1                               // allocation error
    beq 99f
    mov x4,#0                      // counter byte string 2
3:
    ldrb w3,[x1,x4]                // load byte string 2
    cbz x3,4f                      // zero final ?
    strb w3,[x5,x4]                // store byte string 2 in heap
    add x4,x4,1                    // increment counter 1
    b 3b                           // no -> loop
4:
    mov x2,#0                      // counter byte string 1
5:
    ldrb w3,[x6,x2]                // load byte string 1
    strb w3,[x5,x4]                // store byte string in heap
    cbz x3,6f                    // zero final ?
    add x2,x2,1                    // no -> increment counter 1
    add x4,x4,1                    // no -> increment counter 2
    b 5b                           // no -> loop
6:                                 // recopie heap in string 1
    mov x2,#0                      // counter byte string 
7:
    ldrb w3,[x5,x2]                // load byte string in heap
    strb w3,[x6,x2]                // store byte string 1
    cbz x3,100f                    // zero final ?
    add x2,x2,1                    // no -> increment counter 1
    b 7b                           // no -> loop
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:
British Museum.
The rosetta stone is at British Museum.

Action!

PROC Append(CHAR ARRAY text,suffix)
  BYTE POINTER srcPtr,dstPtr
  BYTE len

  len=suffix(0)
  IF text(0)+len>255 THEN
    len=255-text(0)
  FI
  IF len THEN
    srcPtr=suffix+1
    dstPtr=text+text(0)+1
    MoveBlock(dstPtr,srcPtr,len)
    text(0)==+suffix(0)
  FI
RETURN

PROC Prepend(CHAR ARRAY text,prefix)
  CHAR ARRAY tmp(256)

  SCopy(tmp,text)
  SCopy(text,prefix)
  Append(text,tmp)
RETURN

PROC TestPrepend(CHAR ARRAY text,preffix)
  PrintF("Source ""%S"" at address %H%E",text,text)
  PrintF("Prepend ""%S""%E",preffix)
  Prepend(text,preffix)
  PrintF("Result ""%S"" at address %H%E",text,text)
  PutE()
RETURN

PROC Main()
  CHAR ARRAY text(256)

  text(0)=0
  TestPrepend(text,"World!")
  TestPrepend(text,"Hello ")
RETURN
Output:

Screenshot from Atari 8-bit computer

Source "" at address $2A8A
Prepend "World!"
Result "World!" at address $2A8A

Source "World!" at address $2A8A
Prepend "Hello "
Result "Hello World!" at address $2A8A

Ada

In Ada, a variable of type String cannot change its length. So the variable S which we will change, need to be of the type Unbounded_String. Thus the need for conversions from String literal to Unbounded_String for initialization, and from Unbounded_String to String for printing.

with Ada.Text_IO; with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;

procedure Prepend_String is   
   S: Unbounded_String := To_Unbounded_String("World!"); 
begin
   S := "Hello " & S;-- this is the operation to prepend "Hello " to S. 
   Ada.Text_IO.Put_Line(To_String(S));
end Prepend_String;
Output:
Hello World!

ALGOL 68

Works with: ALGOL 68 version Revision 1.
Works with: ALGOL 68G version Any - tested with release algol68g-2.7.
Works with: ELLA ALGOL 68 version Any (with appropriate job cards).

File: String_prepend.a68

#!/usr/bin/a68g --script #
# -*- coding: utf-8 -*- #

STRING str := "12345678";
"0" +=: str;
print(str)
Output:
012345678

AppleScript

AppleScript text is immutable, so prepending is only possible by creating a new text through concatenation of the variable's existing contents to the other string:

set aVariable to "world!"
set aVariable to "Hello " & aVariable
return aVariable
Output:
"Hello world!"

It's a similar situation with NSString class in AppleScriptObjC. This has various ways of achieving the same thing, probably the most sensible of which is the first of the following:

use AppleScript version "2.4" -- OS X 10.10 (Yosemite) or later
use framework "Foundation"

set aVariable to current application's class "NSString"'s stringWithString:("world!")
set aVariable to aVariable's stringByReplacingCharactersInRange:({0, 0}) withString:("Hello ")
-- return aVariable as text

-- Or:
set aVariable to current application's class "NSString"'s stringWithString:("world!")
set aVariable to current application's class "NSString"'s stringWithFormat_("%@%@", "Hello ", aVariable)
-- return aVariable as text

-- Or:
set aVariable to current application's class "NSString"'s stringWithString:("world!")
set aVariable to aVariable's stringByReplacingOccurrencesOfString:("^") withString:("Hello ") ¬
    options:(current application's NSRegularExpressionSearch) range:({0, 0})
-- return aVariable as text

But there's also an NSMutableString class. This has 'replace' versions of the 'stringByReplacing' methods above and also this insertString:atIndex: method:

use AppleScript version "2.4" -- OS X 10.10 (Yosemite) or later
use framework "Foundation"

set aVariable to current application's class "NSMutableString"'s stringWithString:("world!")
tell aVariable to insertString:("Hello ") atIndex:(0)
return aVariable as text
Output:
"Hello world!"

Arturo

a: "World"
a: "Hello" ++ a
print a

b: "World"
b: append "Hello" b
print a

c: "World"
prefix 'c "Hello"
print c

d: "World"
print prefix d "Hello"
Output:
HelloWorld
HelloWorld
HelloWorld
HelloWorld

Asymptote

string s1 = " World!";
write("Hello" + s1);
write("Hello", s1);
string s2 = "Hello" + s1;
write(s2);

AutoHotkey

s := "foo"
s := s "bar"
Msgbox % s
Output:
foobar

AWK

# syntax: GAWK -f STRING_PREPEND.AWK
BEGIN {
    s = "bar"
    s = "foo" s
    print(s)
    exit(0)
}
Output:
foobar

BaCon

s$ = "prepend"
s$ = "String " & s$
PRINT s$
Output:
String prepend

BASIC

S$ = " World!"
S$ = "Hello" + S$
PRINT S$
Output:
Hello World!

Applesoft BASIC

100 LET S$=" World!"
110 LET S$="Hello"+S$
120 PRINT S$

BASIC256

a$ = " World!"
a$ = "Hello"; a$
print a$

# would also be valid 
a$ = "Hello" + a$
# and
a$ = "Hello" & a$

Chipmunk Basic

Works with: Chipmunk Basic version 3.6.4
Works with: Applesoft BASIC
Works with: BASICA
Works with: GW-BASIC
Works with: QBasic
Works with: MSX BASIC
10 A$ = " World!"
20 A$ = "Hello" + A$
30 PRINT A$

GW-BASIC

Works with: PC-BASIC version any
Works with: Applesoft BASIC
Works with: BASICA
Works with: Chipmunk Basic
Works with: QBasic
Works with: MSX BASIC
10 A$ = " World!"
20 A$ = "Hello" + A$
30 PRINT A$

IS-BASIC

100 LET S$=" World!"
110 LET S$="Hello"&S$
120 PRINT S$

MSX Basic

Works with: MSX BASIC version any
Works with: Applesoft BASIC
Works with: BASICA
Works with: Chipmunk Basic
Works with: QBasic
10 A$ = " World!"
20 A$ = "Hello" + A$
30 PRINT A$

Run BASIC

Works with: BASIC256
Works with: Liberty BASIC
Works with: QB64
Works with: QBasic
Works with: Yabasic
a$ = " World!"
a$ = "Hello" + a$
print a$

' en RB, LB and BASIC256 would also be valid
a$ = "Hello"; a$

Quite BASIC

Works with: BASICA
Works with: Chipmunk Basic
Works with: GW-BASIC
Works with: MSX BASIC
Works with: QBasic
10 LET A$ = " World!"
20 LET A$ = "Hello" + A$
30 PRINT A$

True BASIC

Works with: BASIC256
LET a$ = " World!"
LET a$ = "Hello" & a$
PRINT a$
END

Yabasic

Works with: BASIC256
Works with: Liberty BASIC
Works with: QB64
Works with: QBasic
Works with: Run BASIC
a$ = " World!"
a$ = "Hello" + a$
print a$

Binary Lambda Calculus

BLC program

18 16 46 80 05 bc bc fd f6 e0 67 6d 61

based on https://github.com/tromp/AIT/blob/master/rosetta/catstrings.lam prepends "ma" to "gma" to output "magma".

Bracmat

  World!:?string
& str$("Hello " !string):?string
& out$!string
Hello World!

C

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

int main()
{
    char str[100]="my String";
    char *cstr="Changed ";
    char *dup;
    sprintf(str,"%s%s",cstr,(dup=strdup(str)));
    free(dup);
    printf("%s\n",str);
    return 0;
}
Output:
Changed my String

C#

using System;

namespace PrependString
{
    class Program
    {
        static void Main(string[] args)
        {
            string str = "World";
            str = "Hello " + str;
            Console.WriteLine(str);
            Console.ReadKey();
        }
    }
}
Hello World

C++

include <vector>
#include <algorithm>
#include <string>
#include <iostream>

int main( ) {
   std::vector<std::string> myStrings { "prepended to" , "my string" } ;
   std::string prepended = std::accumulate( myStrings.begin( ) , 
	 myStrings.end( ) , std::string( "" ) , []( std::string a , 
	    std::string b ) { return a + b ; } ) ;
   std::cout << prepended << std::endl ;
   return 0 ;
}
Output:
prepended tomy string

Clojure

A pure function implementation with immutability

(defn str-prepend [a-string, to-prepend]
  (str to-prepend a-string))

REPL demonstrations with mutability in mind

a) with the atom data structure

(def s (atom "World"))
(swap! s #(str "Hello, " %))

user=> @s
user=> "Hello, Wolrd"

b) with the ref data structure

(def s (ref "World"))
(dosync (alter s #(str "Hello " %)))

user=> @s
user=> "Hello World"

COBOL

       identification division.
       program-id. prepend.
       data division.
       working-storage section.
       1 str pic x(30) value "World!".
       1 binary.
        2 len pic 9(4) value 0.
        2 scratch pic 9(4) value 0.
       procedure division.
       begin.
           perform rev-sub-str
           move function reverse ("Hello ") to str (len + 1:)
           perform rev-sub-str
           display str
           stop run
           .

       rev-sub-str.
           move 0 to len scratch
           inspect function reverse (str)
           tallying scratch for leading spaces
               len for characters after space
           move function reverse (str (1:len)) to str
           .
       end program prepend.
Hello World!
Works with: GNU Cobol version 2.0
       >>SOURCE FREE
PROGRAM-ID. prepend.

DATA DIVISION.
WORKING-STORAGE SECTION.
01  str                                 PIC X(30) VALUE "world!".

PROCEDURE DIVISION.
    MOVE FUNCTION CONCATENATE("Hello, ", str) TO str
    DISPLAY str
    .
END PROGRAM prepend.

ColdFusion

Classic tag based CFML

<cfoutput>
	<cfset who = "World!">
	#"Hello " & who#
</cfoutput>
Output:
Hello World! 

Script Based CFML

<cfscript>
	who = "World!";
	greeting = "Hello " & who;
	writeOutput( greeting );
</cfscript>
Output:
Hello World! 

Common Lisp

A macro is necessary in order to prepend a string in-place:

(defmacro prependf (s &rest strs)
  "Prepend the given string variable with additional strings. The string variable is modified in-place."
  `(setf ,s (concatenate 'string ,@strs ,s)))

(defvar *str* "foo")
(prependf *str* "bar")
(format T "~a~%" *str*)
Output:
barfoo

D

import std.stdio;

void main() {
    string s = "world!";
    s = "Hello " ~ s; 
    writeln(s);
}
Output:
Hello world!

Delphi

program String_preappend;

{$APPTYPE CONSOLE}

uses
  System.SysUtils;

type
  TStringHelper = record helper for string
    procedure Preappend(str: string);
  end;

{ TStringHelper }

procedure TStringHelper.Preappend(str: string);
begin
  Self := str + self;
end;

begin
  var h: string;

  // with + operator
  h := 'World';
  h := 'Hello ' + h;
  writeln(h);

  // with a function concat
  h := 'World';
  h := concat('Hello ', h);
  writeln(h);

  // with helper
  h := 'World';
  h.Preappend('Hello ');
  writeln(h);
  readln;
end.
Output:
Hello World
Hello World
Hello World

Dyalect

var s = "world!"
s = "Hello " + s
print(s)

Déjà Vu

local :s "world!"
set :s concat( "Hello " s)
!print s
Output:
Hello world!

EasyLang

string$ = "Lang"
string$ = "Easy" & string$
print string$
Output:
EasyLang

EchoLisp

define-syntax-rule 
    (set!-string-prepend a before) 
    (set! a (string-append before a)))
    #syntax:set!-string-prepend

(define name "Presley")
     name
(set!-string-prepend name "Elvis ")
name
     "Elvis Presley"

ed

Port of #sed solution.

s/^/String literal/

Elena

ELENA 6.x:

import extensions;
import extensions'text;
 
public program()
{
    var s := "World";
    s := "Hello " + s;
    console.writeLine(s);
 
    // Alternative way
    var s2 := StringWriter.load("World");
    s2.insert(0, "Hello ");
    console.writeLine(s2);
    console.readChar()
}

Elixir

str1 = "World!"
str = "Hello, " <> str1
Output:

"Hello, World!"

Emacs Lisp

While strings in Emacs Lisp are mutable, they're fixed size. Therefore the concat function creates a new string and the existing string must be referenced twice:

(defvar str "bar")
(setq str (concat "foo" str))
str ;=> "foobar"

This can be hidden by using a macro such as cl-callf2 which expands into the above code:

Library: cl-lib
(require 'cl-lib)

(defvar str "bar")
(cl-callf2 concat "foo" str)
str ;=> "foobar"

Buffers can be thought of as expandable strings:

(let ((buf (get-buffer-create "*foo*")))
  (with-current-buffer buf
    (insert "bar"))
  (with-current-buffer buf
    (goto-char (point-min))
    (insert "foo")
    (buffer-string)))
;; => "foobar"

EMal

text greeting = "world"
^|basic concatenation|^
writeLine("hello " + greeting)
^|changing the text in place|^
writeLine(greeting.insert(0, "hello "))
writeLine(greeting)
Output:
hello world
hello world
hello world

Erlang

Output:
1> S = "world".
"world"
2> "Hello " ++ S.
"Hello world"

ERRE

......
S$=" World!"
S$="Hello"+S$
PRINT(S$)
......
Output:
Hello World!

F#

let mutable s = "world!"
s <- "Hello, " + s
printfn "%s" s

Factor

"world"
"Hello " prepend

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 = "fun "
s = s + "Falcon"
> s
Output:
fun Falcon
[Finished in 0.2s]

Forth

Forth has no string prepend word, but adding it is not difficult. This demonstration starts from the low level operations that Forth gives us and quickly builds a simple set of "WORDS" (sub-routines) that let us move strings from address to address. Strings are just an address on the data stack so we can reference them as many times as we need to. Our prepend word makes use of the Return stack as a temporary storage for the address of the string we want to prepend. Standard Forth also provides a named general purpose buffer called PAD, so we make use of that too. With this PREPEND becomes part of the language.

\ the following functions are commonly native to a Forth system. Shown for completeness

: C+!     ( n addr -- ) dup c@ rot + swap c! ;             \ primitive: increment a byte at addr by n

: +PLACE  ( addr1 length addr2 -- )                        \ Append addr1 length to addr2
          2dup 2>r  count + swap move 2r> c+! ;

: PLACE   ( addr1 len addr2 -- )                           \ addr1 and length, placed at addr2 as counted string
          2dup 2>r  1+  swap  move  2r> c! ;

\ Example begins here
: PREPEND ( addr len addr2 -- addr2)
           >R                                              \ push addr2 to return stack
           PAD PLACE                                       \ place the 1st string in PAD
           R@  count PAD +PLACE                            \ append PAD with addr2 string
           PAD count R@   PLACE                            \ move the whole thing back into addr2
           R> ;                                            \ leave a copy of addr2 on the data stack

: writeln ( addr -- ) cr count type ;                      \ syntax sugar for testing

Test our language extensions interactively at the console

256 buffer: string1 ok                                     
s" needs no introduction!" string1 place  ok                
string1 writeln 
needs no introduction! ok

s" This string "  string1 prepend writeln
This string needs no introduction! ok

Fortran

Early inability

Early Fortran had almost no ability to manipulate text except via overwriting text literals in a FORMAT statement used in a READ, that would then appear when the same FORMAT statement was used in a WRITE (!) perhaps as a heading.

Initial difficulty

With Fortran IV came the ability to use arrays of integers and the A1 format code in READ and WRITE statements for them. With sixteen-bit integers, one might use A2 and so forth, but the numerical values of the integers would not be convenient especially if the sign bit was involved. This would be even more difficult with floating-point variables. Still, the desire for good headings and annotations and flexible layout flogged one onwards. Following the Pascal "Hello world!" example, one might proceed somewhat as follows:

      INTEGER*4 I,TEXT(66)
      DATA TEXT(1),TEXT(2),TEXT(3)/"Wo","rl","d!"/

      WRITE (6,1) (TEXT(I), I = 1,3)
    1 FORMAT ("Hello ",66A2)

      DO 2 I = 1,3
    2   TEXT(I + 3) = TEXT(I)
      TEXT(1) = "He"
      TEXT(2) = "ll"
      TEXT(3) = "o "

      WRITE (6,3) (TEXT(I), I = 1,6)
    3 FORMAT (66A2)
      END

This old-style source is acceptable to the F90 compiler as it stands. By chance, two characters per integer fits nicely but in many cases having one character per variable is easier for manipulation. So, as usual with Fortran, it's all done with arrays. The DATA statement demonstrates that a quoted string is acceptable as a value for an integer; it is just a matter of bit patterns, and this type miscegnation will work with floating-point variables also though resulting in even stranger numerical values. Looking more closely, note that an INTEGER*4 variable can hold four eight-bit characters but only two-character text literals have been specified. Unlike integer constants, which might be considered to have leading zero digits, text literals are deemed to have trailing spaces as needed: "Wo" is deemed to be "Wo " to make up to the recipient's capacity for four characters, and when format code A2 is specified, the leftmost two characters in the variable are taken. The strange ideas of "little-endianism" have never flourished on mainframes! Thus, if the format code were to be A4, then "Wo " would appear, not " Wo".

The first output (to standard output: unit 6) thus prepends the text "Hello " via the workings of the nominated FORMAT statement without a further mention of variable TEXT, itself not being modified in this action. Thus, this is an example of a single-mention possibility.

Some versions of Fortran offered the ability to write to a variable such as an array rather than to a nominated output unit, via a statement like WRITE (TEXT,1) (TEXT(I),I = 1,3), which array could then itself be written to the actual output via normal statements. This would involve a working variable within the routines for formatted I/O to hold the output, and thus provides one of the reasons that Fortran I/O implementations seldom enable re-entrancy - as with a WRITE statement whose output expression list includes a function evaluation, which function itself attempts to WRITE something, say to a log file, with both WRITE statements employing formatting statements. More modern compilers now require the recipient for this sort of WRITE statement to be of type CHARACTER, so the older style is blocked - and re-entrancy is still a problem.

Still another variant involved writing to unit number zero, which did not actually send anything to an output recipient. Instead, the scratchpad used by the formatted I/O system would retain whatever was produced, which could then be read back via unit number zero. Indeed, reading from unit zero would reveal whatever had been the last line of the previous I/O statement. This would be of interest if a format error had been reported on a READ during some mass data acquisition, so that the error message could show the problematic input that had been obtained rather than just complain. But this facility was not common, and did not become a part of the F90 standard. Perhaps a BACKSPACE and re-read to a text variable will work instead...

Retreating from FORMAT usage to the case of manipulating a "string" variable so as to prepend a given text to the working variable, first the existing content must be moved right to make room (again, an even number of characters is involved) which is achieved via the DO-loop, using certain constants. If on the other hand, text were to be removed from the front, then a loop would be needed to shift the surviving content leftwards. In doing this, one must pay attention to any overlaps and the direction of the loop! By chance, this exercise starts the placement after the end of the existing text but if instead the shift were to be two units, then the first-placed unit would land atop the tail end of the existing text. Thus, for rightwards shifts, one should start with the end of the surviving text and work back to its start.

Having made space, the next statements merely assign some bit patterns to elements of TEXT, and then the result is revealed, again using known constants instead of the associated variables of the more general approach. The result from the two WRITE statements is of course

Hello world!
Hello world!

Character facility

With F77 came the CHARACTER type...

      CHARACTER*66 TEXT
      TEXT = "World!"
      TEXT = "Hello "//TEXT
      WRITE (6,*) TEXT
      END

This means that variable TEXT has space for 66 characters, addressed as TEXT(first:last) starting with one. There is no associated string length facility, so the first assignment places the six characters of the supplied literal, followed by spaces all the way to the end of TEXT. Alternatively, TEXT(1:6) = "World!" would place only six characters, leaving the rest of TEXT to hold whatever it may. This would probably be unsuitable for the next statement, which prepends "Hello " to the content of TEXT (including positions past six) and assigns the result to TEXT, overwriting its previous content - with the aid of a temporary working area. Although in principle there could be cunning schemes that update the recipient "in place" with a minimum of character copying to and fro, this doesn't happen. Only characters up to the capacity of the recipient will be transferred from the expression's result, and if the result is shorter than the capacity of the recipient, trailing spaces will be added. All of this is extra effort! And when TEXT is written out, all 66 characters will be sent forth. It is useful to have a function that locates the last non-blank character!

Modern

With F90, and standardised in F2003, came extensions that enable a variable to be "cut-to-fit" on each usage. The first assignment would discard any storage associated with TEXT and re-assign space matching the size of the expression's result, so TEXT would have six characters. In the next statement, the expression would be evaluated and produce twelve characters (six from "Hello ", and the six of the current size of TEXT), then the current storage for text would be discarded and TEXT re-allocated to be of size twelve. At some cost in overhead. On the other hand, rather than copy the result of an expression from the scratchpad to the recipient, with re-allocation, the recipient variable could be repointed to the result area: no copying needed.

FreeBASIC

' FB 1.05.0 Win64

Var s = "prepend"
s = "String " + s
Print s 
Sleep
Output:
String prepend

Free Pascal

Free Pascal supports everything shown in § Pascal (except the string schema data type, string(20) must be written like here). Furthermore, using the compiler directive {$COperators} the following is possible, too:

var
	line: string[20];
begin
	line := 'Hello ';
	{$COperators on}
	line += 'world!';
	writeLn(line)
end.

FutureBasic

include "NSLog.incl"

void local fn DoIt
  CFStringRef s = @"world!"
  s = fn StringByAppendingString( @"Hello ", s )
  NSLog(@"%@",s)
end fn

fn DoIt

HandleEvents
Output:
Hello world!

Gambas

Click this link to run this code

Public Sub Main()
Dim sString1 As String = "world!"
Dim sString2 As String = "Hello "

sString1 = sString2 & sString1

Print sString1

End

Output:

Hello world!

Go

s := "world!"
s = "Hello, " + s

Haskell

Prelude> let f = (++" World!")
Prelude> f "Hello"
Output:
"Hello world!"

Icon and Unicon

s := "world!"
s := "Hello, " || s

To demonstrate how this could be done with only one reference to the variable during the prepend:

procedure main()
   s := ", world"
   s[1:1] ||:= "Hello"
   write(s)
end
Output:
prompt$ unicon -s prepend.icn -x
Hello, world

Another take on it, using String Scanning:

procedure main()
   (s := ", world") ?:= "Hello" || tab(0)
   write(s)
end
Output:
prompt$ unicon -s prepend.icn -x
Hello, world

J

   s=: 'value'
   s
value
   s=: 'new ',s
   s
new value

Java

Java does not have a prepend method.
The most logical way to prepend a string value is with basic concatenation.

String string = "def";
string = "abc" + string;

You could also use the String.concat method.

String string = "def";
string = "abc".concat(string);

You could use the StringBuilder class which provides an insert method.

StringBuilder string = new StringBuilder();
string.append("def");
string.insert(0, "abc");

Additionally, you could use the String.format or String.formatted methods.

String string = "def";
string = String.format("abc%s", string);
String string = "def";
string = "abc%s".formatted(string);

All of these will produce the following output.

abcdef

JavaScript

// No built-in prepend
var s=", World"
s = "Hello" + s
print(s);

jq

"world!" as $s
| "Hello " + $s

Julia

s = "world!"
s = "Hello " * s

K

    s: "world!"
"world!"
    "Hello " , s
"Hello world!"

Kotlin

// version 1.0.6

fun main(args: Array<String>) {
    var s = "Obama"
    s = "Barack " + s
    println(s)

    // It's also possible to use this standard library function
    // though this is not what it's really intended for
    var t = "Trump"
    t = t.prependIndent("Donald ")
    println(t)
}
Output:
Barack Obama
Donald Trump

Lambdatalk

{def str World}
-> str

Hello, {str}
-> Hello, World

Lasso

local(x = ', World!')
#x->merge(1,'Hello')
#x // Hello, World!

LFE

Using the concatenation operator:

> (set s "world")
"world"
> (++ "hello " s)
"hello world"

Using the concatenation function:

> (set s "world")
"world"
> (string:concat "hello " s)
"hello world"

Lingo

str = "world!"
put "Hello " before str
put str
-- "Hello world!"

LiveCode

The idiomatic way is to use "before"

put "world" into x
put "hello" before x
put x // hello world

Lua

By concatenation:

s = "12345678"
s = "0" .. s
print(s)

By string formatting:

s = "12345678"
s = string.format("%s%s", "0", s)
print(s)

By list joining:

s = "12345678"
s = table.concat({"0", s})
print(s)
Output:

of each solution

    012345678

M2000 Interpreter

Module PrependString {
      A$="Hello"
      A$+=" World"
      Print A$
}
PrependString
Output:
Hello World

Maple

l := " World";
m := cat("Hello", l);
n := "Hello"||l;
o := `||`("Hello", l);
Output:
                            " World"
                         "Hello World"
                         "Hello World"
                         "Hello World"

Mathematica/Wolfram Language

a = "any text value";
a =  "another string literal" <> a  (* using concatenation (no built-in prepend) *)
Output:
"another string literalany text value"

Mercury

:- module string_prepend.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
:- import_module string.
main(!IO) :-
    S = "World!\n",
    io.write_string("Hello " ++ S, !IO).
Output:
Hello World!

Nanoquery

Nanoquery has no idiomatic way to prepend one string to another.

s1 = " a test"
s1 = "this is" + s1

println s1
Output:
this is a test

Neko

The plus operator, +, concatenates string data. Neko treats strings as mutable fixed length buffers, so some care would need to be taken when prepending variables to variables as there may be buffer sizing to take into consideration. For literals, this is not a concern, as the literals are placed in buffers of the proper size by the compiler.

/**
 <doc><p>String prepend in Neko</pre></doc>
**/

var str = ", world"
str = "Hello" + str
$print(str, "\n")
Output:
prompt$ nekoc string-prepend.neko
prompt$ neko string-prepend.n
Hello, world

NetRexx

s_ = 'world!'
s_ = 'Hello, 's_
say s_
Output:
Hello, world!

NewLISP

(setq str "bar")
(push "foo" str)
(println str)

Nim

# Direct way.
var str1, str2 = "12345678"
str1 = "0" & str1
echo str1

# Using "insert".
str2.insert("0")
echo str2
Output:
012345678
012345678

Objeck

class Prepend  {
  function : Main(args : String[]) ~ Nil {
    s := "world!";
    "Hello {$s}"->PrintLine();
  }
}
Hello World!

OCaml

let () =
  let s = ", world" in
  let s = "Hello" ^ s in
  print_endline s

Oforth

" World" "Hello" swap + println
Output:
Hello World

PARI/GP

Not supported in GP.

s = "world!";
s = Str("Hello, ", s)
Output:
%1 = "Hello, world!"

Pascal

See also Free Pascal

Works with: Extended Pascal
program stringPrepend(output);
var
	line: string(20);
begin
	line := 'Hello ';
	line := line + 'world!';
	writeLn(line); 
	
	line := 'Hello ';
	writeStr(line, line, 'world!');
	writeLn(line)
end.
Output:
Hello world!
Hello world!

PascalABC.NET

##
var s := '12345678';
s := '0' + s;
Print(s);
Output:
012345678 


Perl

use strict;
use warnings;
use feature ':all';

# explicit concatentation
$_ = 'bar';
$_ = 'Foo' . $_;
say;


# lvalue substr
$_ = 'bar';
substr $_, 0, 0, 'Foo';
say;


# interpolation as concatenation
# (NOT safe if concatenate sigils)
$_ = 'bar';
$_ = "Foo$_";
say;
Output:
Foobar
Foobar
Foobar

Phix

Library: Phix/basics
string s = "World"
s = "Hello "&s

NB: s = prepend(s,"Hello ") gives typecheck: s is {"Hello ",87'W',111'o',114'r',108'l',100'd'}, of length 6, rather than the "Hello World" of length 11 you probably wanted.
       - and likewise s = prepend("Hello ",s) is not only the wrong way round but dies with typecheck: s is {"World",72'H',101'e',108'l',108'l',111'o',32' '} (length 7).

Phixmonti

/# Rosetta Code problem: https://rosettacode.org/wiki/String_prepend
by Galileo, 10/2022 #/

"Hello " var s
s "world" chain var s
s print

Picat

As usual there are a couple ways of doing this. The most common is probable to use string concatenation (++), but append/3 might be useful if backtracking is needed.

go =>
  
  S = "123456789",
  println(S),
  S := "A" ++ S,  
  println(S),

  % append
  append("B",S,T),
  S := T,
  println(S),

  % insert at position
  S := insert(S,1,'C'), % note: must be a char to keep it a proper string
  println(S),
  % insert many characters
  S := insert_all(S,1,"DE"),
  println(S),
  nl.
Output:
123456789
A123456789
BA123456789
CBA123456789
DECBA123456789

PicoLisp

(setq Str1 "12345678!")
(setq Str1 (pack "0" Str1))
(println Str1)
Output:
"012345678!"

PL/I

Pre_Cat: procedure options (main); /* 2 November 2013 */
   declare s character (100) varying;
   s = ' bowl';
   s = 'dust' || s;
   put (s);
end Pre_Cat;
dust bowl

Plain TeX

\def\prepend#1#2{% #1=string  #2=macro containing a string
	\def\tempstring{#1}%
	\expandafter\expandafter\expandafter
	\def\expandafter\expandafter\expandafter
	#2\expandafter\expandafter\expandafter
	{\expandafter\tempstring#2}%
}
\def\mystring{world!}
\prepend{Hello }\mystring
Result : \mystring
\bye

Here is an equivalent code with eTeX capabilities:

\def\prepend#1#2{% #1=string  #2=macro containing a string
	\edef#2{\unexpanded{#1}\unexpanded\expandafter{#2}}%
}
\def\mystring{world!}
\prepend{Hello }\mystring
Result : \mystring
\bye

PowerShell

$str = "World!"
$str = "Hello, " + $str
$str
Hello, World!

Prolog

Works with: SWI-Prolog

In its admirable wisdom, Prolog is generally unfriendly to state mutations and destructive assignment. However, it is also very flexible. Using the traditional representation of strings as lists of character codes, and the non-logical predicate `setarg/3`, we can destructively set the head and tail of the list to achieve a mutation of the variable holding the string. I define an operator for the purpose:

:- op(200, xfx, user:(=+)).

%% +Prepend =+ +Chars
%
%    Will destructively update Chars
%    So that Chars = Prepend prefixed to Chars.
%    eazar001 in ##prolog helped refine this approach.

[X|Xs] =+ Chars :-
  append(Xs, Chars, Rest),
  nb_setarg(2, Chars, Rest),
  nb_setarg(1, Chars, X).

Example of this abomination in action:

?- Str = `World!`, `Hello, ` =+ Str.
Str = "Hello, World!".

Note: I can't imagine when I would want to do this in Prolog.

PureBasic

S$ = " World!"
S$ = "Hello" + S$
If OpenConsole()
  PrintN(S$)

  Print(#CRLF$ + #CRLF$ + "Press ENTER to exit"): Input()
  CloseConsole()
EndIf
Output:
Hello World!

Python

File: string_prepend.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

s = "12345678"
s = "0" + s  # by concatenation
print(s)
Output:
012345678

QB64

s$ = "prepend"
s$ = "String " + s$
Print s$
Output:
String prepend

Quackery

$ "with a rubber duck."
$ "One is never alone "
swap join
echo$
Output:
One is never alone with a rubber duck.

Racket

;there is no built-in way to set! prepend in racket
(define str "foo")
(set! str (string-append "bar " str))
(displayln str)

;but you can create a quick macro to solve that problem
(define-syntax-rule (set-prepend! str value)
  (set! str (string-append value str)))

(define macrostr " bar")
(set-prepend! macrostr "foo")
(displayln macrostr)
Output:
bar foo
foo bar

Raku

(formerly Perl 6)

# explicit concatentation
$_ = 'byte';
$_ = 'kilo' ~ $_;
.say;

# interpolation as concatenation
$_ = 'buck';
$_ = "mega$_";
.say;

# lvalue substr
$_ = 'bit';
substr-rw($_,0,0) = 'nano';
.say;

# regex substitution
$_ = 'fortnight';
s[^] = 'micro';
.say;

# reversed append assignment
$_ = 'cooper'; 
$_ [R~]= 'mini';
.say;
Output:
kilobyte
megabuck
nanobit
microfortnight
minicooper

Red

Red []
s: "world"
insert s "hello "
print s
Output:
hello world

REXX

zz= 'llo world!'          /*─────────────── using literal abuttal.────────────*/
zz= 'he'zz                /*This won't work if the variable name is  X  or  B */
say zz


gg = "llo world!"         /*─────────────── using literal concatenation.──────*/
gg = 'he' || gg
say gg


aString= 'llo world!'     /*─────────────── using variable concatenation.─────*/
bString= "he"
aString= bString || aString
say aString

output

hello world!
hello world!
hello world!

Ring

aString = "World!"
bString = "Hello, " + aString
see bString + nl

RPL

In HP-48+ RPL versions, the STO+ instruction can either append or prepend a string to a variable containing already a string.

"def" 'Z' STO
"abc" 'Z' STO+
Z

Output

 1: "abcdef"

Ruby

There is a method for prepending a string, aptly named "prepend".

str = "llo world"
str.prepend("He")
p str #=> "Hello world"

Rust

let mut s = "World".to_string();
s.insert_str(0, "Hello ");
println!("{}", s);

Scala

Evaluation in Scala worksheet

  val s = "World" // Immutables are recommended   //> s  : String = World
  val f2 = () => ", " //Function assigned to variable
                                                  //> f2  : () => String = <function0>
  val s1 = "Hello" + f2() + s                     //> s1  : String = Hello, World
  println(s1);                                    //> Hello, World

sed

There are no variables in sed, just two distinct locations for storing a string: The "pattern space" and the "hold space". To prepend a string literal to the pattern space, the s command can be used:

s/^/String Literal/

To prepend a string literal to the hold space, it needs to be exchanged with the pattern space, before and after the operation:

x
s/^/String Literal/
x

Seed7

$ include "seed7_05.s7i";

const proc: main is func
  local
    var string: s is "world!";
  begin
    s := "Hello " & s; 
    writeln(s);
  end func;
Output:
Hello world!

Sidef

var str = 'llo!';
str.sub!(/^/, 'He');
say str;

or

var str = 'llo!';
str.prepend!('He');
say str;
Output:
Hello!

SNOBOL4

    s = ', World!'
    OUTPUT = s = 'Hello' s
END
Output:
Hello, World!

SparForte

As a structured script.

#!/usr/local/bin/spar
pragma annotate( summary, "string_prepend" )
       @( description, "Create a string variable equal to any text value." )
       @( description, "" )
       @( description, "Prepend the string variable with another string " )
       @( description, "literal." )
       @( category, "tutorials" )
       @( author, "Ken O. Burtch" )
       @( see_also, "http://rosettacode.org/wiki/String_prepend" );
pragma license( unrestricted );

pragma software_model( nonstandard );
pragma restriction( no_external_commands );

procedure string_prepend is
  world : constant string := "World!";
  hello : constant string := "Hello ";
  s : string;
begin
  -- Using concatenation
  s := world;
  s := hello & @;
  ? s;

  -- Using strings library
  s := world;
  s := strings.insert( @, 1, hello );
  ? s;

  command_line.set_exit_status( 0 );
end string_prepend;
Output:
$ spar string_prepend.sp          
Hello World!
Hello World!

Standard ML

> val s="any text" ;
val s = "any text": string
> "prepended " ^ s;
val it = "prepended any text": string

Stata

sca s="Vita Brevis"
sca s="Ars Longa "+s
di s

Ars Longa Vita Brevis

Swift

Works with: Swift version 5
var str = ", World"
str = "Hello" + str
print(str)
Output:
Hello, World!
Works with: Swift version 1
var str = ", World"
str = "Hello \(str)"
println(str)
Output:
Hello, World!

Tcl

Concatenation is a fundamental feature of Tcl's basic language syntax.

set s "llo world"
set s "he$s"
puts $s
Output:
hello world

Ursa

decl string s

# set s to "world"
set s "world"

# prepend "hello "
set s (+ "hello " s)

# outputs "hello world"
out s endl console

VBA

Function StringPrepend()
Dim s As String
s = "bar"
s = "foo" & s
Debug.Print s
End Function

VBScript

s = "bar"
s = "foo" & s
WScript.Echo s
Output:
foobar

V (Vlang)

mut s := "world!"
s = "Hello, " + s
println(s)
Output:
Hello, world!

Wart

s <- "12345678"
s <- ("0" + s)

Wren

var s = "world!"
s = "Hello, " + s
System.print(s)
Output:
Hello, world!

Xojo

Dim s As String = "bar"
s = "foo" + s
MsgBox(s)
Output:
foobar

XPL0

include xpllib;
char S, T(80);
[S:= "world!";
S:= StrCat(StrCopy(T,"Hello, "), S);
Text(0, S);
]
Output:
Hello, world!

zkl

s:="bar"; s="foo" + s;           s.println();
s:="bar"; s=String("foo",s);     s.println();
s:="bar"; s="%s%s".fmt("foo",s); s.println();
   // a Data is a byte buffer/editor:
s:=Data(Void,"bar").insert(0,"foo").text; s.println();
Output:
foobar
foobar
foobar
foobar