Hello123World

1.

@echo off
(For /f "tokens=1* delims=:" %%i in ('findstr /n ".*" a.txt') do if "%%i"=="3" (echo welcome & echo\ &echo "加入内容") Else (echo %%j))>1.txt
pause
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2.

@echo off
For /f %%i in (a.txt) do Set "%%i" 2>nul
echo %abcd%
pause
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