[amel27]

если порядок не важен:

Код:

@echo off
(
for /f "tokens=1* delims=[] " %%a in ('^<123.txt find /n /v ""') do set "$.%%b=."
for /f "tokens=*" %%a in ('set $.') do (set "$a=%%a"
  setlocal EnableDelayedExpansion
  set "$a=!$a:~2,-2!"
  echo/!$a!
  endlocal
))>456.txt