How to substitute variable contents in a Windows batch file

Question

I\'m writing a simple script to substitute text in an environment variable with other text. The trouble I get is with the substituted or substituted text being pulled from o

Answer 1

:: Use perl on %var% =~ s/$old/$new/

set var=The fat cat
set old=fat
set new=thin

ECHO before=%var%

for /f "delims=" %%m in ('echo %var% ^|perl -pe "s/%old%/%new%/" ') do set var=%%m

ECHO after=%var% 

Output:

before=The fat cat
after=The thin cat