For once I agree with Tuxman
Though I used AWK more because AWK scripts are easier to maintain. Another option is Minitrue
by Andrew Pipkin, which is specifically designed for the job. It's worth reading Eric Pement's sed page
for more details on this; keep paging down to the "related batch editing files" section which mentions Minitrue amongst others. On no account overlook Mr. Pement's supplementary page on Minitrue workarounds
. Mr. Pement appears unaware that Jason Hood has made an updated version of MiniTrue
that fixes some issues, though I haven't tried it.