Bash command for regular expression substitution

Question

What bash command can be used for regex substitution on a pipe?

     cat foo.txt | someprogram

Answer 1

You probably want

sed 's/exp1/exp2/g' foo.txt > foo2.txt

Read more at Sed tutorial, Another tutorial, and A small tutorial at Linux HOWTOs

Answer 2

You can also use perl one liners if you find you want more regular expression features than sed provides. See this link for a comparison. nik's example would look like:

perl -ple 's/exp1/exp2/g' foo > foo2.txt

Answer 3

The program you are looking for is sed.