sed: Print comment header block using `sed`

If you include help documentation as a comment block at the top of a file, you can use the following sed to print it.

sed -E '
  /^#!/ d       # ignore shebang
  /^# ?/ {      # match first comment prefix
    :header     # (label for start of main loop)
    // {        # match comment prefix (reuse regex)
     s///       # remove comment prefix (reuse regex)
     n          # read next line (implicit print)
     b header   # (next loop!)
    }
    Q           # quit, now first comment block is finished
  }
 ' $0           # process on $0 i.e. the script itself