Strip comments from a string

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Task
Strip comments from a string
You are encouraged to solve this task according to the task description, using any language you may know.

The task is to remove text that follow any of a set of comment markers, (in these examples either a hash or a semicolon) from a string or input line.


Whitespace debacle:   There is some confusion about whether to remove any whitespace from the input line.

As of 2 September 2011, at least 8 languages (C, C++, Java, Perl, Python, Ruby, sed, UNIX Shell) were incorrect, out of 36 total languages, because they did not trim whitespace by 29 March 2011 rules. Some other languages might be incorrect for the same reason.

Please discuss this issue at Talk:Strip comments from a string.

  • From 29 March 2011, this task required that: "The comment marker and any whitespace at the beginning or ends of the resultant line should be removed. A line without comments should be trimmed of any leading or trailing whitespace before being produced as a result." The task had 28 languages, which did not all meet this new requirement.
  • From 28 March 2011, this task required that: "Whitespace before the comment marker should be removed."
  • From 30 October 2010, this task did not specify whether or not to remove whitespace.


The following examples will be truncated to either "apples, pears " or "apples, pears".

(This example has flipped between "apples, pears " and "apples, pears" in the past.)

apples, pears # and bananas
apples, pears ; and bananas


Related task



Ada[edit]

with Ada.Text_IO;
procedure Program is
Comment_Characters : String := "#;";
begin
loop
declare
Line : String := Ada.Text_IO.Get_Line;
begin
exit when Line'Length = 0;
Outer_Loop : for I in Line'Range loop
for J in Comment_Characters'Range loop
if Comment_Characters(J) = Line(I) then
Ada.Text_IO.Put_Line(Line(Line'First .. I - 1));
exit Outer_Loop;
end if;
end loop;
end loop Outer_Loop;
end;
end loop;
end Program;

ALGOL 68[edit]

Works with: ALGOL 68 version Revision 1 - no extensions to language used.
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny.
Works with: ELLA ALGOL 68 version Any (with appropriate job cards) - tested with release 1.8-8d
#!/usr/local/bin/a68g --script #
 
PROC trim comment = (STRING line, CHAR marker)STRING:(
INT index := UPB line+1;
char in string(marker, index, line);
FOR i FROM index-1 BY -1 TO LWB line
WHILE line[i]=" " DO index := i OD;
line[:index-1]
);
 
CHAR q = """";
 
print((
q, trim comment("apples, pears # and bananas", "#"), q, new line,
q, trim comment("apples, pears ; and bananas", ";"), q, new line,
q, trim comment("apples, pears and bananas ", ";"), q, new line,
q, trim comment(" ", ";"), q, new line, # blank string #
q, trim comment("", ";"), q, new line # empty string #
))
 
CO Alternatively Algol68g has available "grep"
;STRING re marker := " *#", line := "apples, pears # and bananas";
INT index := UPB line;
grep in string(re marker, line, index, NIL);
print((q, line[:index-1], q, new line))
END CO

Output:

"apples, pears"
"apples, pears"
"apples, pears and bananas"
""
""


Applesoft BASIC[edit]

10 LET C$ = ";#"
20 S$(1)="APPLES, PEARS # AND BANANAS"
30 S$(2)="APPLES, PEARS ; AND BANANAS"
40 FOR Q = 1 TO 2
50 LET S$ = S$(Q)
60 GOSUB 100"STRIP COMMENTS
70 PRINT S$
80 NEXT Q
90 END
 
100 IF S$ = "" THEN RETURN
110 FOR I = 1 TO LEN(S$)
120 LET A$ = MID$(S$, I, 1)
130 FOR J = 1 TO LEN(C$)
140 LET F$ = MID$(C$, J, 1)
150 IF A$ <> F$ THEN NEXT J
160 IF A$ = F$ THEN 200
170 NEXT I
200 LET I = I - 1
210 GOSUB 260"STRIP
220 IF S$ = "" THEN RETURN
230 FOR I = I TO 0 STEP -1
240 LET A$ = MID$(S$, I, 1)
250 IF A$ = " " THEN NEXT I
260 LET S$ = MID$(S$, 1, I)
270 RETURN

AutoHotkey[edit]

Delims := "#;"
str := "apples, pears # and bananas"
str2:= "apples, pears, `; and bananas" ; needed to escape the ; since that is AHK's comment marker
msgbox % StripComments(Str,Delims)
msgbox % StripComments(Str2,Delims)
; The % forces expression mode.
 
 
StripComments(String1,Delims){
Loop, parse, delims
{
If Instr(String1,A_LoopField)
EndPosition := InStr(String1,A_LoopField) - 1
Else
EndPosition := StrLen(String1)
StringLeft, String1, String1, EndPosition
}
return String1
}

Output:

apples, pears 
apples, pears, 


AutoIt[edit]

It was always said in discussion, the task is not really stripping comments. It's only a truncation.

 
Dim $Line1 = "apples, pears # and bananas"
Dim $Line2 = "apples, pears ; and bananas"
 
_StripAtMarker($Line1)
_StripAtMarker($Line2)
 
Func _StripAtMarker($_Line, $sMarker='# ;')
Local $aMarker = StringSplit($sMarker, ' ')
Local $iPos
For $i = 1 To $aMarker[0]
$iPos = StringInStr($_Line, $aMarker[$i])
If $iPos Then
ConsoleWrite($_Line & @CRLF)
ConsoleWrite( StringStripWS( StringLeft($_Line, $iPos -1), 2) & @CRLF)
EndIf
Next
EndFunc ;==>_StripAtMarker
 

Output:

apples, pears # and bananas
apples, pears
apples, pears ; and bananas
apples, pears

Here is a really language-related solution to parse script lines and delete comments. A comment in line in AutoIt starts with an semicolon. But it may be possible, that a semicolon is part of a string in a parameter from an function-call/function-headline or in an assignment. That means: the comment starts with the first semicolon outside a string.

 
Dim $aLines[4] = _
[ _
"$a = $b + $c ; Comment line 1", _
"Dim $s1 = 'some text; tiled with semicolon', $s2 = 'another text; also tiled with semicolon' ; Comment line 2 - semicolon as part of assignment", _
"_SomeFunctionCall('string parameter with ;', $anotherParam) ; Comment line 3 - semicolon as part parameter in an function call", _
"Func _AnotherFunction($param1=';', $param2=';', $param3=';') ; Comment line 4 - semicolon as default value in parameter of a function headline" _
]
 
For $i = 0 To 3
ConsoleWrite('+> Line ' & $i+1 & ' full:' & @CRLF & '+>' & $aLines[$i] & @CRLF)
ConsoleWrite('!> without comment:' & @CRLF & '!>' & _LineStripComment($aLines[$i]) & @CRLF & @CRLF)
Next
 
 
Func _LineStripComment($_Line)
; == tile line by all included comment marker
Local $aPartsWithMarker = StringSplit($_Line, ';')
Local $sNoComment
 
; == if no comment marker: return full line
If $aPartsWithMarker[0] = 0 Then Return $_Line
 
; == check if string in part, if is'nt: following part(s) are comment
For $i = 1 To $aPartsWithMarker[0]
If Not StringRegExp($aPartsWithMarker[$i], "('|\x22)") Then
If $i = 1 Then
Return StringStripWS($aPartsWithMarker[$i], 2)
Else
Return StringStripWS($sNoComment & $aPartsWithMarker[$i], 2)
EndIf
Else
; == check if next leftside string delimiter has uneven count
Local $iLen = StringLen($aPartsWithMarker[$i])
Local $fDetectDelim = False, $sStringDelim, $iDelimCount, $sCurr
For $j = $iLen To 1 Step -1
$sCurr = StringMid($aPartsWithMarker[$i], $j, 1)
If Not $fDetectDelim Then
If $sCurr = "'" Or $sCurr = '"' Then
$sStringDelim = $sCurr
$iDelimCount += 1
$fDetectDelim = True
EndIf
Else
If $sCurr = $sStringDelim Then $iDelimCount += 1
EndIf
Next
If Mod($iDelimCount, 2) Then
; == uneven count: so it masks the comment marker
$sNoComment &= $aPartsWithMarker[$i] & ';'
Else
; == even count: all following is comment
Return StringStripWS($sNoComment & $aPartsWithMarker[$i], 2)
EndIf
EndIf
Next
EndFunc ;==>_LineStripComment
 

Output:

+> Line 1 full:
+>$a = $b + $c ; Comment line 1
>> without comment:
>>$a = $b + $c

+> Line 2 full:
+>Dim $s1 = 'some text; tiled with semicolon', $s2 = 'another text; also tiled with semicolon' ; Comment line 2 - semicolon as part of assignment
>> without comment:
>>Dim $s1 = 'some text; tiled with semicolon', $s2 = 'another text; also tiled with semicolon'

+> Line 3 full:
+>_SomeFunctionCall('string parameter with ;', $anotherParam) ; Comment line 3 - semicolon as part parameter in an function call
>> without comment:
>>_SomeFunctionCall('string parameter with ;', $anotherParam)

+> Line 4 full:
+>Func _AnotherFunction($param1=';', $param2=';', $param3=';') ; Comment line 4 - semicolon as default value in parameter of a function headline
>> without comment:
>>Func _AnotherFunction($param1=';', $param2=';', $param3=';')

AWK[edit]

#!/usr/local/bin/awk -f
{
sub("[ \t]*[#;].*$","",$0);
print;
}

BBC BASIC[edit]

      marker$ = "#;"
PRINT FNstripcomment("apples, pears # and bananas", marker$)
PRINT FNstripcomment("apples, pears ; and bananas", marker$)
PRINT FNstripcomment(" apples, pears ", marker$)
END
 
DEF FNstripcomment(text$, delim$)
LOCAL I%, D%
FOR I% = 1 TO LEN(delim$)
D% = INSTR(text$, MID$(delim$, I%, 1))
IF D% text$ = LEFT$(text$, D%-1)
NEXT I%
WHILE ASC(text$) = 32 text$ = MID$(text$,2) : ENDWHILE
WHILE LEFT$(text$) = " " text$ = RIGHT$(text$) : ENDWHILE
= text$

Bracmat[edit]

(   "    apples, pears # and bananas
oranges, mangos ; and a durian"
 : ?text
& :?newText
& ( non-blank
= %@:~(" "|\t|\r|\n)
)
& ( cleanUp
=
. @(!arg:?arg ("#"|";") ?)
& @(rev$!arg:? (!non-blank ?:?arg))
& @(rev$!arg:? (!non-blank ?:?arg))
& !arg {You could write & "[" !arg "]" to prove that the blanks are stripped.}
)
& whl
' ( @(!text:?line (\r|\n) ?text)
& !newText \n cleanUp$!line:?newText
)
& !newText \n cleanUp$!text:?newText
& out$(str$!newText)
);

Output:

apples, pears
oranges, mangos

C[edit]

#include<stdio.h>
 
int main()
{
char ch, str[100];
int i;
 
do{
printf("\nEnter the string :");
fgets(str,100,stdin);
for(i=0;str[i]!=00;i++)
{
if(str[i]=='#'||str[i]==';')
{
str[i]=00;
break;
}
}
printf("\nThe modified string is : %s",str);
printf("\nDo you want to repeat (y/n): ");
scanf("%c",&ch);
fflush(stdin);
}while(ch=='y'||ch=='Y');
 
return 0;
}

Output:

Enter the string :apples, pears # and bananas

The modified string is : apples, pears
Do you want to repeat (y/n): y

Enter the string :apples, pears ; and bananas

The modified string is : apples, pears
Do you want to repeat (y/n): n

C++[edit]

#include <iostream>
#include <string>
 
std::string strip_white(const std::string& input)
{
size_t b = input.find_first_not_of(' ');
if (b == std::string::npos) b = 0;
return input.substr(b, input.find_last_not_of(' ') + 1 - b);
}
 
std::string strip_comments(const std::string& input, const std::string& delimiters)
{
return strip_white(input.substr(0, input.find_first_of(delimiters)));
}
 
int main( ) {
std::string input;
std::string delimiters("#;");
while ( getline(std::cin, input) && !input.empty() ) {
std::cout << strip_comments(input, delimiters) << std::endl ;
}
return 0;
}

Sample output:

apples, pears # and bananas
apples, pears
apples, pears ; and bananas
apples, pears

C#[edit]

 
using System.Text.RegularExpressions;
 
string RemoveComments(string str, string delimiter)
{
//regular expression to find a character (delimiter) and
// replace it and everything following it with an empty string.
//.Trim() will remove all beginning and ending white space.
return Regex.Replace(str, delimiter + ".+", string.Empty).Trim();
}
 

Sample output:

Console.WriteLine(RemoveComments("apples, pears # and bananas", "#"));
Console.WriteLine(RemoveComments("apples, pears ; and bananas", ";"));
apples, pears
apples, pears

Clojure[edit]

> (apply str (take-while #(not (#{\# \;} %)) "apples # comment"))
"apples "

Common Lisp[edit]

(defun strip-comments (s cs)
"Truncate s at the first occurrence of a character in cs."
(defun comment-char-p (c)
(some #'(lambda (x) (char= x c)) cs))
(let ((pos (position-if #'comment-char-p s)))
(subseq s 0 pos)))
Output:

Use the function in combination with STRING-TRIM to fulfill the task requirements.

> (string-trim '(#\Space #\Tab) (strip-comments "apples, pears # and bananas" "#;"))

"apples, pears"
> (string-trim '(#\Space #\Tab) (strip-comments "apples, pears ; and bananas" "#;"))

"apples, pears"
> (string-trim '(#\Space #\Tab) (strip-comments "  apples, pears and bananas  " "#;"))

"apples, pears and bananas"

D[edit]

import std.stdio, std.regex;
 
string remove1LineComment(in string s, in string pat=";#") {
const re = "([^" ~ pat ~ "]*)([" ~ pat ~ `])[^\n\r]*([\n\r]|$)`;
return s.replace(regex(re, "gm"), "$1$3");
}
 
void main() {
const s = "apples, pears # and bananas
apples, pears ; and bananas "
;
 
writeln(s, "\n====>\n", s.remove1LineComment());
}
Output:
apples, pears # and bananas
apples, pears ; and bananas 
====>
apples, pears 
apples, pears 

Delphi[edit]

program StripComments;
 
{$APPTYPE CONSOLE}
 
uses
SysUtils;
 
function DoStripComments(const InString: string; const CommentMarker: Char): string;
begin
Result := Trim(Copy(InString,1,Pos(CommentMarker,InString)-1));
end;
 
begin
Writeln('apples, pears # and bananas --> ' + DoStripComments('apples, pears # and bananas','#'));
Writeln('');
Writeln('apples, pears ; and bananas --> ' + DoStripComments('apples, pears ; and bananas',';'));
Readln;
end.

DWScript[edit]

function StripComments(s : String) : String;
begin
var p := FindDelimiter('#;', s);
if p>0 then
Result := Trim(Copy(s, 1, p-1))
else Result := Trim(s);
end;
 
PrintLn(StripComments('apples, pears # and bananas'));
PrintLn(StripComments('apples, pears ; and bananas'));

Erlang[edit]

 
-module( strip_comments_from_string ).
 
-export( [task/0] ).
 
task() ->
io:fwrite( "~s~n", [keep_until_comment("apples, pears and bananas")] ),
io:fwrite( "~s~n", [keep_until_comment("apples, pears # and bananas")] ),
io:fwrite( "~s~n", [keep_until_comment("apples, pears ; and bananas")] ).
 
 
 
keep_until_comment( String ) -> lists:takewhile( fun not_comment/1, String ).
 
not_comment( $# ) -> false;
not_comment( $; ) -> false;
not_comment( _ ) -> true.
 
Output:
17> strip_comments_from_string:task().
apples, pears and bananas
apples, pears 
apples, pears 

F#[edit]

let stripComments s =
s
|> Seq.takeWhile (fun c -> c <> '#' && c <> ';')
|> Seq.map System.Char.ToString
|> Seq.fold (+) ""

Fantom[edit]

Using a regular expression:

class Main
{
static Str removeComment (Str str)
{
regex := Regex <|(;|#)|>
matcher := regex.matcher (str)
if (matcher.find)
return str[0..<matcher.start]
else
return str
}
 
public static Void main ()
{
echo (removeComment ("String with comment here"))
echo (removeComment ("String with comment # here"))
echo (removeComment ("String with comment ; here"))
}
}

Fortran[edit]

!****************************************************
module string_routines
!****************************************************
implicit none
private
public :: strip_comments
contains
!****************************************************
 
function strip_comments(str,c) result(str2)
implicit none
character(len=*),intent(in) :: str
character(len=1),intent(in) :: c !comment character
character(len=len(str)) :: str2
 
integer :: i
 
i = index(str,c)
if (i>0) then
str2 = str(1:i-1)
else
str2 = str
end if
 
end function strip_comments
 
!****************************************************
end module string_routines
!****************************************************
 
!****************************************************
program main
!****************************************************
! Example use of strip_comments function
!****************************************************
use string_routines, only: strip_comments
implicit none
 
write(*,*) strip_comments('apples, pears # and bananas', '#')
write(*,*) strip_comments('apples, pears ; and bananas', ';')
 
!****************************************************
end program main
!****************************************************

output:

apples, pears
apples, pears

FreeBASIC[edit]

' FB 1.05.0 Win64
 
Sub stripComment(s As String, commentMarkers As String)
If s = "" Then Return
Dim i As Integer = Instr(s, Any commentMarkers)
If i > 0 Then
s = Left(s, i - 1)
s = Trim(s) '' removes both leading and trailing whitespace
End If
End Sub
 
Dim s(1 To 4) As String = _
{ _
"apples, pears # and bananas", _
"apples, pears ; and bananas", _
"# this is a comment", _
" # this is a comment with leading whitespace" _
}
 
For i As Integer = 1 To 4
stripComment(s(i), "#;")
Print s(i), " => Length ="; Len(s(i))
Next
 
Print
Print "Press any key to quit"
Sleep
Output:
apples, pears  => Length = 13
apples, pears  => Length = 13
               => Length = 0
               => Length = 0

Go[edit]

package main
 
import (
"fmt"
"strings"
"unicode"
)
 
const commentChars = "#;"
 
func stripComment(source string) string {
if cut := strings.IndexAny(source, commentChars); cut >= 0 {
return strings.TrimRightFunc(source[:cut], unicode.IsSpace)
}
return source
}
 
func main() {
for _, s := range []string{
"apples, pears # and bananas",
"apples, pears ; and bananas",
"no bananas",
} {
fmt.Printf("source:  %q\n", s)
fmt.Printf("stripped: %q\n", stripComment(s))
}
}

Output:

source:   "apples, pears # and bananas"
stripped: "apples, pears"
source:   "apples, pears ; and bananas"
stripped: "apples, pears"
source:   "no bananas"
stripped: "no bananas"

Groovy[edit]

def stripComments = { it.replaceAll(/\s*[#;].*$/, '') }

Testing:

assert 'apples, pears' == stripComments('apples, pears # and bananas')
assert 'apples, pears' == stripComments('apples, pears ; and bananas')

Haskell[edit]

ms = ";#"
 
main = getContents >>=
mapM_ (putStrLn . takeWhile (`notElem` ms)) . lines

Icon and Unicon[edit]

# strip_comments: 
# return part of string up to first character in 'markers',
# or else the whole string if no comment marker is present
procedure strip_comments (str, markers)
return str ? tab(upto(markers) | 0)
end
 
procedure main ()
write (strip_comments ("apples, pears and bananas", cset ("#;")))
write (strip_comments ("apples, pears # and bananas", cset ("#;")))
write (strip_comments ("apples, pears ; and bananas", cset ("#;")))
end

Output:

apples, pears   and bananas
apples, pears 
apples, pears 

Inform 7[edit]

Home is a room.
 
When play begins:
strip comments from "apples, pears # and bananas";
strip comments from "apples, pears ; and bananas";
end the story.
 
To strip comments from (T - indexed text):
say "[T] -> ";
replace the regular expression "<#;>.*$" in T with "";
say "[T][line break]".

Since square brackets have a special meaning in strings, Inform's regular expression syntax uses angle brackets for character grouping.

J[edit]

Solution 1 (mask & filter):
strip=: [email protected](#~  *./\@:[email protected]&';#')
Solution 2 (index & cut):
strip=: [email protected]({.~  <./@i.&';#')
Example:
   dquote strip '  apples, pears # and bananas'  NB. quote result to show stripped whitespace
"apples, pears"
strip ' apples, pears ; and bananas'
"apples, pears"

Java[edit]

import java.io.*;
 
public class StripLineComments{
public static void main( String[] args ){
if( args.length < 1 ){
System.out.println("Usage: java StripLineComments StringToProcess");
}
else{
String inputFile = args[0];
String input = "";
try{
BufferedReader reader = new BufferedReader( new FileReader( inputFile ) );
String line = "";
while((line = reader.readLine()) != null){
System.out.println( line.split("[#;]")[0] );
}
}
catch( Exception e ){
e.printStackTrace();
}
}
}
}


JavaScript[edit]

function stripComments(s) {
var re1 = /^\s+|\s+$/g; // Strip leading and trailing spaces
var re2 = /\s*[#;].+$/g; // Strip everything after # or ; to the end of the line, including preceding spaces
return s.replace(re1,'').replace(re2,'');
}
 
 
var s1 = 'apples, pears # and bananas';
var s2 = 'apples, pears ; and bananas';
 
alert(stripComments(s1) + '\n' + stripComments(s2));
 

A more efficient version that caches the regular expressions in a closure:

var stripComments = (function () {
var re1 = /^\s+|\s+$/g;
var re2 = /\s*[#;].+$/g;
return function (s) {
return s.replace(re1,'').replace(re2,'');
};
}());
 

A difference with the two versions is that in the first, all declarations are processed before code is executed so the function declaration can be after the code that calls it. However in the second example, the expression creating the function must be executed before the function is available, so it must be before the code that calls it.

jq[edit]

If your version of jq has regex support, the task can be accomplished with the following one-liner:

sub("[#;].*";"") | sub("^\\s+";"") |  sub("\\s+$";"")

Otherwise, we can define strip_comment as a jq filter, as follows. For clarity, the helper functions are presented as top-level functions.

# define whitespace here as a tab, space, newline, return or form-feed character:
def is_whitespace: . as $in | " \n\r\f\t" | index($in);
 
def ltrim:
if .[0:1] | is_whitespace then (.[1:]|ltrim) else . end;
 
def rtrim:
if .[length-1:] | is_whitespace then .[0:length-1]|rtrim else . end;
 
def trim: ltrim | rtrim;
 
def strip_comment:
index("#") as $i1 | index(";") as $i2
| (if $i1 then if $i2 then [$i1, $i2] | min
else $i1
end
else $i2
end ) as $ix
| if $ix then .[0:$ix] else . end
| trim;

Example:

" abc ; def # ghi" | strip_comment
Output:
"abc"

Julia[edit]

striplinecomment is designed to be flexible and robust. By default # and ; are considered comment defining characters, but any characters can be used by passing them as the string cchars. All such characters are escaped in the regular expression used to eliminate comments to allow characters special to the Regex language (e.g. ^, $, [) to be used as a comment character.

 
function striplinecomment{T<:String,U<:String}(a::T, cchars::U="#;")
b = strip(a)
0 < length(cchars) || return b
for c in cchars
r = Regex(@sprintf "\\%c.*" c)
b = replace(b, r, "")
end
strip(b)
end
 
tests = {"apples, pears # and bananas",
"apples, pears ; and bananas",
" apples, pears & bananas ",
" # "}
 
for t in tests
s = striplinecomment(t)
println("Testing \"", t, "\":")
println(" \"", s, "\"")
end
 
Output:
Testing "apples, pears # and bananas":
    "apples, pears"
Testing "apples, pears ; and bananas":
    "apples, pears"
Testing "  apples, pears & bananas   ":
    "apples, pears & bananas"
Testing " # ":
    ""

Kotlin[edit]

For the avoidance of doubt and in line with what the current description of this task appears to be, the following program is designed to remove comments from a string which in Kotlin are:

1. // this is a comment (to the end of the line)

2. /* this is a comment */

3. /* outer comment /* nested comment */ more outer comment */

It then removes whitespace from the beginning and end of the resulting string:

// version 1.0.6
 
val r = Regex("""(/\*.*\*/|//.*$)""")
 
fun stripComments(s: String) = s.replace(r, "").trim()
 
fun main(args: Array<String>) {
val strings = arrayOf(
"apples, pears // and bananas",
" apples, pears /* and bananas */",
"/* oranges */ apples // pears and bananas ",
" \toranges /*apples/*, pears*/*/and bananas"
)
for (string in strings) println(stripComments(string))
}
Output:
apples, pears
apples, pears
apples
oranges and bananas

Liberty BASIC[edit]

string1$ = "apples, pears # and bananas"
string2$ = "pears;, " + chr$(34) + "apples ; " + chr$(34) + " an;d bananas"
commentMarker$ = "; #"
Print parse$(string2$, commentMarker$)
End
 
Function parse$(string$, commentMarker$)
For i = 1 To Len(string$)
charIn$ = Mid$(string$, i, 1)
If charIn$ = Chr$(34) Then
inQuotes = Not(inQuotes)
End If
If Instr(commentMarker$, charIn$) And (inQuotes = 0) Then Exit For
next i
parse$ = Left$(string$, (i - 1))
End Function

Lua[edit]

comment_symbols = ";#"
 
s1 = "apples, pears # and bananas"
s2 = "apples, pears ; and bananas"
 
print ( string.match( s1, "[^"..comment_symbols.."]+" ) )
print ( string.match( s2, "[^"..comment_symbols.."]+" ) )

Maple[edit]

> use StringTools in map( [email protected], [ "\t\t   apples, pears \t# and bananas", " apples, pears ; and bananas  \t" ], "#;" ) end; 
["apples, pears", "apples, pears"]

Mathematica[edit]

a = "apples, pears # and bananas
apples, pears ; and bananas";
b = StringReplace[a, RegularExpression["[ ]+[#;].+[\n]"] -> "\n"];
StringReplace[b, RegularExpression["[ ]+[#;].+$"] -> ""] // FullForm

Output:

"apples, pears\napples, pears"

MATLAB / Octave[edit]

function line = stripcomment(line) 
e = min([find(line=='#',1),find(line==';',1)]);
if ~isempty(e)
e = e-1;
while isspace(line(e)) e = e - 1; end;
line = line(1:e);
end;
end;
 

Output:

>> stripcomment('apples, pears # and bananas\n')
ans = apples, pears
>> stripcomment('apples, pears ; and bananas\n')
ans = apples, pears

Nim[edit]

import strutils
 
proc removeComments(line, sep): string =
line.split(sep)[0].strip(leading = false)
 
echo removeComments("apples, pears # and bananas", '#')
echo removeComments("apples, pears ; and bananas", ';')

OCaml[edit]

let strip_comments str =
let len = String.length str in
let rec aux print i =
if i >= len then () else
match str.[i] with
| '#' | ';' ->
aux false (succ i)
| '\n' ->
print_char '\n';
aux true (succ i)
| c ->
if print then print_char c;
aux print (succ i)
in
aux true 0
 
let () =
strip_comments "apples, pears # and bananas\n";
strip_comments "apples, pears ; and bananas\n";
;;

or with an imperative style:

let strip_comments =
let print = ref true in
String.iter (function
| ';' | '#' -> print := false
| '\n' -> print_char '\n'; print := true
| c -> if !print then print_char c)

Oforth[edit]

: stripComments(s, markers)
| firstMarker |
markers map(#[ s indexOf ]) reduce(#min) ->firstMarker
s firstMarker ifNotNull: [ left(firstMarker 1 - ) ] strip ;
Output:
>stripComments("apples, pears # and bananas", "#") println
apples, pears

>stripComments("apples, pears ;  and bananas # and oranges", "#;") println
apples, pears

Pascal[edit]

See Delphi

Perl[edit]

while (<>)
{
s/[#;].*$//s; # remove comment
s/^\s+//; # remove leading whitespace
s/\s+$//; # remove trailing whitespace
print
}

Perl 6[edit]

$*IN.slurp.subst(/ \h* <[ # ; ]> \N* /, '', :g).print

Phix[edit]

Added a couple of things that can go wrong with something nowhere near sufficiently smart or for that matter language-specific enough.
A line comment inside a block comment (eg " /* left -- right */") could also be very dodgy, and perhaps vice versa.

function strip_comments(string s, sequence comments={"#",";"})
for i=1 to length(comments) do
integer k = match(comments[i],s)
if k then
s = s[1..k-1]
s = trim_tail(s)
end if
end for
return s
end function
 
?strip_comments("apples, pears # and bananas")
?strip_comments("apples, pears ; and bananas")
?strip_comments("apples, pears and bananas ")
?strip_comments(" WS_CAPTION = #00C00000, -- = WS_BORDER+WS_DLGFRAME")
?strip_comments(" WS_CAPTION = #00C00000, -- = WS_BORDER+WS_DLGFRAME",{"--"})
?strip_comments(" title = \"--Title--\"",{"--"})
Output:
"apples, pears"
"apples, pears"
"apples, pears and bananas  "
"    WS_CAPTION ="
"    WS_CAPTION = #00C00000,"
"  title = \""

PicoLisp[edit]

(for Str '("apples, pears # and bananas" "apples, pears ; and bananas")
(prinl (car (split (chop Str) "#" ";"))) )

Output:

apples, pears 
apples, pears 

PL/I[edit]

k = search(text, '#;');
if k = 0 then put skip list (text);
else put skip list (substr(text, 1, k-1));

Prolog[edit]

Works with: SWI Prolog

This version is implemented as a state automata to strip multiple lines of comments.

stripcomment(A,B) :- stripcomment(A,B,a).
stripcomment([A|AL],[A|BL],a) :- \+ A=0';, \+ A=0'# , \+ A=10, \+ A=13 , stripcomment(AL,BL,a).
stripcomment([A|AL], BL ,a) :- ( A=0';; A=0'#), \+ A=10, \+ A=13 , stripcomment(AL,BL,b).
stripcomment([A|AL], BL ,b) :- \+ A=10, \+ A=13 , stripcomment(AL,BL,b).
stripcomment([A|AL],[A|BL],_M):- ( A=10; A=13), stripcomment(AL,BL,a).
stripcomment([],[],_M).
start :-
In = "apples, pears ; and bananas
apples, pears # and bananas",
stripcomment(In,Out),
format("~s~n",[Out]).

Output:

?- start.
apples, pears 
apples, pears 

This version uses prolog's pattern matching with two append/3 to strip 1 line.

strip_1comment(A,D) :- ((S1=0'#;S1=0';),append(B,[S1|C],A)), \+ ((S2=0'#;S2=0';),append(_X,[S2|_Y],B)) -> B=D; A=D.

At the query console:

?- strip_1comment("apples, pears ; and bananas",O1),format("~s~n",[O1]).
apples, pears 
O1 = [97, 112, 112, 108, 101, 115, 44, 32, 112|...] .
?- strip_1comment("apples, pears # and bananas",O1),format("~s~n",[O1]).
apples, pears 
O1 = [97, 112, 112, 108, 101, 115, 44, 32, 112|...] .

PureBasic[edit]

Procedure.s Strip_comments(Str$)
Protected result$=Str$, l, l1, l2
l1 =FindString(Str$,"#",1)
l2 =FindString(Str$,";",1)
;
; See if any comment sign was found, prioritizing '#'
If l1
l=l1
ElseIf l2
l=l2
EndIf
l-1
If l>0
result$=Left(Str$,l)
EndIf
ProcedureReturn result$
EndProcedure

Implementation

#instring1 ="apples, pears # and bananas"
#instring2 ="apples, pears ; and bananas"
 
PrintN(Strip_comments(#instring1))
PrintN(Strip_comments(#instring2))
Output:
apples, pears
apples, pears

Python[edit]

>>> marker, line = '#', 'apples, pears # and bananas'
>>> line[:line.index(marker)].strip()
'apples, pears'
>>>
>>> marker, line = ';', ' apples, pears ; and bananas'
>>> line[:line.index(marker)].strip()
'apples, pears'

The code above does not handle multiple markers at once; moreover it is going to give an error if a line doesn't contain a marker. Another implementation:

def remove_comments(line, sep):
for s in sep:
line = line.split(s)[0]
return line.strip()
 
# test
print remove_comments('apples ; pears # and bananas', ';#')
print remove_comments('apples ; pears # and bananas', '!')
 

You could also use a regular expression

import re
 
m = re.match(r'^([^#]*)#(.*)$', line)
if m: # The line contains a hash / comment
line = m.group(1)
 

R[edit]

This is most cleanly accomplished using the stringr package.

strip_comments <- function(str)
{
if(!require(stringr)) stop("you need to install the stringr package")
str_trim(str_split_fixed(str, "#|;", 2)[, 1])
}

Example usage:

x <-c(
"apples, pears # and bananas", # the requested hash test
"apples, pears ; and bananas", # the requested semicolon test
"apples, pears and bananas", # without a comment
" apples, pears # and bananas" # with preceding spaces
)
strip_comments(x)

Racket[edit]

 
#lang at-exp racket
 
(define comment-start-rx "[;#]")
 
(define text
@~a{apples, pears # and bananas
apples, pears ; and bananas
})
 
(define (strip-comments text [rx comment-start-rx])
(string-join
(for/list ([line (string-split text "\n")])
(string-trim line (pregexp (~a "\\s*" rx ".*")) #:left? #f))
"\n"))
 
;; Alternatively, do it in a single regexp operation
(define (strip-comments2 text [rx comment-start-rx])
(regexp-replace* (pregexp (~a "(?m:\\s*" rx ".*)")) text ""))
 
(strip-comments2 text) ; -> "apples, pears\napples, pears"
 

Red[edit]

 
Red has an embedded parse engine called Parse.
For more info on the Parse dialect. http://www.red-lang.org/2013/11/041-introducing-parse.html
 
We parse the string and copy all the characters up to the semicolon into the variable str
 
>> parse "apples, pears ; and bananas" [copy str to ";" to end]
== true
>> str
== "apples, pears "

REXX[edit]

version 1[edit]

The first REXX subroutine takes advantage of the fact that there are only two single-character delimiters:

  •   #   (hash or pound sign),
  •   ;     (a semicolon).

The second and third subroutines take a general approach to the (number of) delimiters,
the third subroutine is more straightforward and reads better.
The fourth subroutine is similar to the third version but more idiomatic.

All four subroutines trim leading   and   trailing blanks after stripping the "comments".

/*REXX program  strips  a string  delineated  by a  hash (#)   or   a  semicolon (;).   */
old1= ' apples, pears # and bananas'  ; say ' old ───►'old1"◄───"
new1= stripCom1(old1)  ; say ' 1st version new ───►'new1"◄───"
new2= stripCom2(old1)  ; say ' 2nd version new ───►'new2"◄───"
new3= stripCom3(old1)  ; say ' 3rd version new ───►'new3"◄───"
new4= stripCom4(old1)  ; say ' 4th version new ───►'new4"◄───"
say copies('▒', 62)
old2= ' apples, pears ; and bananas'  ; say ' old ───►'old2"◄───"
new1= stripCom1(old2)  ; say ' 1st version new ───►'new1"◄───"
new2= stripCom2(old2)  ; say ' 2nd version new ───►'new2"◄───"
new3= stripCom3(old2)  ; say ' 3rd version new ───►'new3"◄───"
new4= stripCom4(old2)  ; say ' 4th version new ───►'new4"◄───"
exit /*stick a fork in it, we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
stripCom1: procedure; parse arg x /*obtain the argument (the X string).*/
x=translate(x, '#', ";") /*translate semicolons to a hash (#). */
parse var x x '#' /*parse the X string, ending in hash. */
return strip(x) /*return the stripped shortened string.*/
/*──────────────────────────────────────────────────────────────────────────────────────*/
stripCom2: procedure; parse arg x /*obtain the argument (the X string).*/
d= ';#' /*this is the delimiter list to be used*/
d1=left(d,1) /*get the first character in delimiter.*/
x=translate(x,copies(d1,length(d)),d) /*translates delimiters ──► 1st delim.*/
parse var x x (d1) /*parse the string, ending in a hash. */
return strip(x) /*return the stripped shortened string.*/
/*──────────────────────────────────────────────────────────────────────────────────────*/
stripCom3: procedure; parse arg x /*obtain the argument (the X string).*/
d= ';#' /*this is the delimiter list to be used*/
do j=1 for length(d) /*process each of the delimiters singly*/
_=substr(d,j,1) /*use only one delimiter at a time. */
parse var x x (_) /*parse the X string for each delim. */
end /*j*/ /* [↑] (_) means stop parsing at _ */
return strip(x) /*return the stripped shortened string.*/
/*──────────────────────────────────────────────────────────────────────────────────────*/
stripCom4: procedure; parse arg x /*obtain the argument (the X string).*/
d= ';#' /*this is the delimiter list to be used*/
do k=1 for length(d) /*process each of the delimiters singly*/
p=pos(substr(d,k,1), x) /*see if a delimiter is in the X string*/
if p\==0 then x=left(x,p-1) /*shorten the X string by one character*/
end /*k*/ /* [↑] If p==0, then char wasn't found*/
return strip(x) /*return the stripped shortened string.*/

output

                 old ───► apples, pears # and bananas◄───
     1st version new ───►apples, pears◄───
     2nd version new ───►apples, pears◄───
     3rd version new ───►apples, pears◄───
     4th version new ───►apples, pears◄───
▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒
                 old ───► apples, pears ; and bananas◄───
     1st version new ───►apples, pears◄───
     2nd version new ───►apples, pears◄───
     3rd version new ───►apples, pears◄───
     4th version new ───►apples, pears◄───

version 2[edit]

Call stripd ' apples, pears # and bananas'
Call stripd ' apples, pears and bananas'
Exit
stripd:
Parse Arg old
dlist='#;' /* delimiter list */
p=verify(old,dlist,'M') /* find position of delimiter */
If p>0 Then /* delimiter found */
new=strip(left(old,p-1))
Else
new=strip(old)
Say '>'old'<'
Say '>'new'<'
Return

Ring[edit]

 
aList = 'apples, pears # and bananas'
see aList + nl
see stripComment(aList) + nl
aList = 'apples, pears // and bananas'
see aList + nl
see stripComment(aList) + nl
 
func stripComment bList
nr = substr(bList,"#")
if nr > 0 cList = substr(bList,1,nr-1) ok
nr = substr(bList,"//")
if nr > 0 cList = substr(bList,1,nr-1) ok
return cList
 

Ruby[edit]

class String
def strip_comment( markers = ['#',';'] )
re = Regexp.union( markers ) # construct a regular expression which will match any of the markers
if index = (self =~ re)
self[0, index].rstrip # slice the string where the regular expression matches, and return it.
else
rstrip
end
end
end
 
p 'apples, pears # and bananas'.strip_comment
str = 'apples, pears ; and bananas'
p str.strip_comment
str = 'apples, pears and bananas '
p str.strip_comment
p str.strip_comment('and')
p " \t \n ;".strip_comment
p "".strip_comment
Output:
"apples, pears"
"apples, pears"
"apples, pears and bananas"
"apples, pears"
""
""

Scala[edit]

object StripComments {
def stripComments1(s:String, markers:String =";#")=s takeWhile (!markers.contains(_)) trim
 
// using regex and pattern matching
def stripComments2(s:String, markers:String =";#")={
val R=("(.*?)[" + markers + "].*").r
(s match {
case R(line) => line
case _ => s
}) trim
}
 
def print(s:String)={
println("'"+s+"' =>")
println(" '"+stripComments1(s)+"'")
println(" '"+stripComments2(s)+"'")
}
 
def main(args: Array[String]): Unit = {
print("apples, pears # and bananas")
print("apples, pears ; and bananas")
}
}

Output:

'apples, pears # and bananas' =>
   'apples, pears'
   'apples, pears'
'apples, pears ; and bananas' =>
   'apples, pears'
   'apples, pears'

Scheme[edit]

Works with: Guile
(use-modules (ice-9 regex))
 
(define (strip-comments s)
(regexp-substitute #f
(string-match "[ \t\r\n\v\f]*[#;].*" s) 'pre "" 'post))
 
(display (strip-comments "apples, pears # and bananas"))(newline)
(display (strip-comments "apples, pears ; and bananas"))(newline)
Output:
apples, pears
apples, pears

sed[edit]

#!/bin/sh
# Strip comments
echo "$1" | sed 's/ *[#;].*$//g' | sed 's/^ *//'

Seed7[edit]

$ include "seed7_05.s7i";
 
const func string: stripComment (in string: line) is func
result
var string: lineWithoutComment is "";
local
var integer: lineEnd is 0;
var integer: pos is 0;
begin
lineEnd := length(line);
for pos range 1 to length(line) do
if line[pos] in {'#', ';'} then
lineEnd := pred(pos);
pos := length(line);
end if;
end for;
lineWithoutComment := line[.. lineEnd];
end func;
 
const proc: main is func
local
var string: stri is "apples, pears # and bananas\n\
\apples, pears ; and bananas";
var string: line is ""
begin
writeln(stri);
writeln("====>");
for line range split(stri, '\n') do
writeln(stripComment(line));
end for;
end func;

Output:

apples, pears # and bananas
apples, pears ; and bananas
====>
apples, pears 
apples, pears 

Sidef[edit]

func strip_comment(s) {
(s - %r'[#;].*').strip;
}
 
[" apples, pears # and bananas",
" apples, pears ; and bananas",
" apples, pears "].each { |s|
say strip_comment(s).dump;
};
Output:
"apples, pears"
"apples, pears"
"apples, pears"

Tcl[edit]

proc stripLineComments {inputString {commentChars ";#"}} {
# Switch the RE engine into line-respecting mode instead of the default whole-string mode
regsub -all -line "\[$commentChars\].*$" $inputString "" commentStripped
# Now strip the whitespace
regsub -all -line {^[ \t\r]*(.*\S)?[ \t\r]*$} $commentStripped {\1}
}

Demonstration:

# Multi-line string constant
set input "apples, pears # and bananas
apples, pears ; and bananas"

# Do the stripping
puts [stripLineComments $input]

Output:

apples, pears
apples, pears

The above code has one issue though; it's notion of a set of characters is very much that of the RE engine. That's possibly desirable, but to handle any sequence of characters as a set of separators requires a bit more cleverness.

proc stripLineComments {inputString {commentChars ";#"}} {
# Convert the character set into a transformation
foreach c [split $commentChars ""] {lappend map $c "\uFFFF"}; # *very* rare character!
# Apply transformation and then use a simpler constant RE to strip
regsub -all -line {\uFFFF.*$} [string map $map $inputString] "" commentStripped
# Now strip the whitespace
regsub -all -line {^[ \t\r]*(.*\S)?[ \t\r]*$} $commentStripped {\1}
}

Output in the example is the same as above.

TUSCRIPT[edit]

$$ MODE TUSCRIPT
strngcomment=*
DATA apples, pears # and bananas
DATA apples, pears ; and bananas
 
BUILD S_TABLE comment_char="|#|;|"
 
LOOP s=strngcomment
x=SPLIT (s,comment_char,string,comment)
PRINT string
ENDLOOP

Output:

apples, pears
apples, pears

UNIX Shell[edit]

Works with: bash
Works with: pdksh

Adapted from the Advanced Bash-Scripting Guide, section 10.1 Manipulating Strings.

bash$ a='apples, pears ; and bananas'
bash$ b='apples, pears # and bananas'
bash$ echo ${a%%;*}
apples, pears
bash$ echo ${b%%#*}
apples, pears
bash$

VBScript[edit]

 
Function strip_comments(s,char)
If InStr(1,s,char) > 0 Then
arr = Split(s,char)
strip_comments = RTrim(arr(0))
Else
strip_comments = s
End If
End Function
 
WScript.StdOut.WriteLine strip_comments("apples, pears # and bananas","#")
WScript.StdOut.WriteLine strip_comments("apples, pears ; and bananas",";")
 

zkl[edit]

fcn strip(text,c){  // if c in text, remove it and following text
if (Void!=(n:=text.find(c))) text=text[0,n];
text.strip() // remove leading and trailing white space
}
fcn stripper(text,a,b,c,etc){ // strip a,b,c,etc from text
foreach c in (vm.arglist[1,*]){ text=strip(text,c) }
text
}

Or, if you want the all-in-one stripper:

fcn stripper(text,a,b,c,etc){
vm.arglist[1,*].reduce('wrap(text,c){
if (Void!=(n:=text.find(c))) text[0,n] else text
},text)
.strip()
}
String(">", strip(" apples, pears # and bananas","#"), "<").println();
String(">", stripper(" apples, pears ; and # bananas","#",";"), "<").println();
Output:
>apples, pears<
>apples, pears<