@echo off
for /f "delims=" %%. in (1.txt) do (
set "str=%%."
call,set "str=%%str:*a=%%"
for /f "delims=a" %%{ in ("%%.") do (
set "var=%%{"
call,echo.%%var:0=%%a%%str%%
))
pause>nul

@echo off
for /f "tokens=1,2 delims=a" %%i in (1.txt) do (
if "%%j" neq "" (
set "str=%%i"
call,set "str=%%str:0=%%"
call,echo %%str%%a%%j
) else (
echo a%%i
)
)
pause>nul