How to remove trailing and leading whitespace for

Question

I know how to do this when the variable is pre-defined. However, when asking for the user to enter in some kind of input, how do I trim leading and trailing whitespace? This is what I have so far:

@echo off

set /p input=:
echo. The input is %input% before

::trim left whitespace
for /f "tokens=* delims= " %%a in ("%input%") do set input=%%a
::trim right whitespace (up to 100 spaces at the end)
for /l %%a in (1,1,100) do if "!input:~-1!"==" " set input=!input:~0,-1! 

echo. The input is %input% after

pause

Answer 1

@echo off
setlocal EnableDelayedExpansion
set S=  This  is  a  test
echo %S%.
for /f "tokens=* delims= " %%a in ('echo %S%') do (set b=%%a & set b=!b: =! & echo !b!)
endlocal & goto :EOF

or

@echo off
setlocal EnableDelayedExpansion
set S=  This  is  a  test
echo %S%.
for /f "tokens=* delims= " %%a in ('echo %S%') do (set b=%%a & set b=!b: =_! & echo !b!)
endlocal & goto :EOF