Ah. I'm afraid I misspoke, I meant sed, not awk =/. Not using either language I tend to get confused as to which is which.
As for sed, It appears to have various append commands, insert commands, and lots of other commands, including regexes. It automatically executes on all lines by default but you can specify specific lines.
The more I read perlrun
the more I am convinced that most of desift can be done with command-line flags, including what you mention: executing all lines by default: just the the -n or -p flags
CGI::Application rock the house