@echo off
cd . > b.txt
for /f "delims=" %%a in (a.txt) do (
call :paras "a%%~a"
)
goto :eof
:paras
echo "%~1" |findstr /c:"("|findstr /c:")" > nul
if %errorlevel% equ 0 (
for /f "tokens=1-2* delims=()" %%a in ("%~1") do (
echo %%b >> b.txt
call :paras "a%%~c"
)
)