Remove trailing spaces from a file using Windows batch?

Question

How could I trim all trailing spaces from a text file using the Windows command prompt?

Answer 1

I just found a very nice solution for trimming off white-spaces of a string:
Have you ever called a sub-routine using call and expanded all arguments using %*? You will notice that any leading and/or trailing white-spaces are removed. Any white-spaces occurring in between other characters are preserved; so are all the other command token separators ,, ;, = and also the non-break space (character code 0xFF). This effect I am going to utilise for my script:

@echo off

set "STR="
set /P STR="Enter string: "

rem /* Enable Delayed Expansion to avoid trouble with
rem    special characters: `&`, `<`, `>`, `|`, `^` */
setlocal EnableDelayedExpansion
echo You entered: `!STR!`
call :TRIM !STR!
echo And trimmed: `!RES!`
endlocal

exit /B

:TRIM
set "RES=%*"
exit /B

This script expects a string entered by the user which is then trimmed. This can of course also be applied on lines of a file (which the original question is about, but reading such line by line using for /F is shown in other answers anyway, so I skip this herein). To trim the string on one side only, add a single character to the opposite side prior to trimming and remove it afterwards.

This approach has got some limitations though: it does not handle characters %, !, ^ and " properly. To overcome this, several intermediate string manipulation operations become required:

@echo off
setlocal EnableExtensions DisableDelayedExpansion

set "STR="
set /P STR="Enter string: "

setlocal EnableDelayedExpansion
echo You entered: `!STR!`
set "STR=!STR:%%=%%%%!"
set "STR=!STR:"=""!^"
if not "%STR%"=="%STR:!=%" set "STR=!STR:^=^^^^!"
set "STR=%STR:!=^^^!%"
call :TRIM !STR!
set "RES=!RES:""="!^"
echo And trimmed: `!RES!`
endlocal

endlocal
exit /B

:TRIM
set "RES=%*"
exit /B

---

Update

Both of the above scripts cannot handle the characters &, <, > and |, because call seems to become aborted as soon as such a character appears in an unquoted and unescaped manner.

However, I finally found a way to fix that and come up with an approach that can successfully deal with all characters (except perhaps some control characters, which I did not test):

@echo off
setlocal EnableExtensions EnableDelayedExpansion

rem // The last white-space in `STRING` is a tabulator:
set "RESULT=" & set "STRING=   (<&>"^|)^^!^^^^;,=   ^"
echo Input string: `!STRING!`

rem // Double quotes to avoid troubles with unbalanced ones:
if defined STRING set "STRING=!STRING:"=""!^"
rem // Particularly handle carets and exclamation marks as delayed expansion is enabled:
if defined STRING set "STRING=!STRING:^=^^^^!"
if defined STRING set "STRING=%STRING:!=^^^!%" !
if defined STRING (
    rem // Escape all characters that `call` has got troubles with:
    set "STRING=!STRING:^=^^!"
    set "STRING=!STRING:&=^&!"
    set "STRING=!STRING:<=^=^>!"
    set "STRING=!STRING:|=^|!"
)
rem /* Call the sub-routine here; the strigs `!=!` constitute undefined dummy variables
rem    with an illegal name, which eventually become removed; the purpose of them us to
rem    enable usage of that `call` inside of a `for` loop with the meta-variable `%%S`,
rem    which would otherwise become unintentionally expanded rather than `%%STRING%%`,
rem    which literally contained `%%S`; the `!=!` at the end is just there in case you
rem    want to append another string that could also match another `for` meta-variable;
rem    note that `!!` is not possible as this would be collapsed to a single `!`, so
rem    a (most probably undefined) variable `!STRING%!` would then become expanded: */
call :TRIM %%!=!STRING%%!=!
rem /* The caret doubling done by `call` does not need to be reverted, because due to
rem    doubling of the quotes carets appear unquoted, so implicit reversion occurs here;
rem    of course the doubling of the quotes must eventually be undone: */
if defined RESULT set "RESULT=!RESULT:""="!^"
echo Now trimmed: `!RESULT!`

endlocal
exit /B

:TRIM
    rem // This is the effective line that does the left- and right-trimming:
    set "RESULT=%*" !
    exit /B