On Linux (Debian), how can I prefix the standard output of a command with one or several lines before piping it to a second command?
This is for mailing the output of a command using sendmail like so:
pflogsumm <args> | sendmail <address>
I cannot specify a subject line this way since sendmail extracts header fields from the input it is fed. I thus want to prefix the pflogsumm output using sed.