What GNU/Linux command-line tool would I use for performing a search and replace on a file?

Question

What GNU/Linux command-line tool would I use for performing a search and replace on a file?

Can the search text, and replacement, be specified in a regex format?

Answer 1

Perl was invented for this:

perl -pi -e 's/foo/bar/g;' *.txt

Any normal s/// pattern in those single quotes. You can keep a backup with something like this:

perl -pi.bak -e 's/foo/bar/g;' *.txt

Or pipeline:

cat file.txt | perl -ne 's/foo/bar/g;' | less

But that's really more sed's job.