Search and replace 'dh $@' with sed

Question

I want to replace this string

dh $@

with that one

dh $@ --foobar

I tried this

sed --expression "s/dh $@/dh $@ --foobar/" file

But of course there is the blank and the $ makeing "problems".

Answer 1

Use single quotes around the pattern to avoid shell variable expansion from expanding the $@ to the empty string (or whatever other contents the positional parameters contain.

sed --expression 's/dh $@/dh $@ --foobar/' file

You could also use & in the replacement to avoid needing to duplicate the pattern. ( & in the replacement means the entirety of the match.)

sed --expression 's/dh $@/& --foobar/' file