[Georgio]

Код:

@echo off

set source="1.csv" "2.csv" "3.csv"
set destination="4.csv"
set "delimiter=; "

<nul>%destination% cmd/v/c for /l %%1 in () do @^>nul set/a n+=1^& (^
 for /f "delims=" %%2 in ('"find/n /v "" %source%| findstr/bl [!n!]"')^
  do @^>nul set/a o+=1^& set x=%%2^& if !o! neq 3 (set/p=!x:*]=!!delimiter!)^
   else echo(!x:*]=!!delimiter:~,-1!)^|^| exit/b^& set o=
 
exit/b