Self-documenting shell program by Sam Stephenson https://twitter.com/sstephenson/status/285487626570579968

_selfdoc.sh

# Print the current shell script’s initial comment block, sans leading `# `
sed -ne '/^#/!q;s/.\{1,2\}//;1d;p' < "$0"

example.sh

# Example: executable that aborts with documentation on stderr when no
# required argument is given, but stdin is associated with a terminal.
# On `-h` or `--help`, puts docs to stdout.

abort=0
[[ -z $1 && -t 0 ]] && abort=1

if [[ $abort -gt 0 || $1 = "-h" || $1 = "--help" ]]; then
  sed -ne '/^#/!q;s/.\{1,2\}//;1d;p' < "$0" >&$((abort+1))
  exit $abort
fi