batch script – read line by line

Try this:

@echo off
for /f "tokens=*" %%a in (input.txt) do (
  echo line=%%a
)
pause

because of the tokens=* everything is captured into %a

edit:
to reply to your comment, you would have to do that this way:

@echo off
for /f "tokens=*" %%a in (input.txt) do call :processline %%a

pause
goto :eof

:processline
echo line=%*

goto :eof

:eof

Because of the spaces, you can’t use %1, because that would only contain the part until the first space. And because the line contains quotes, you can also not use :processline "%%a" in combination with %~1. So you need to use %* which gets %1 %2 %3 ..., so the whole line.