safe.bash

#!/bin/bash

set -o errexit -o nounset -o pipefail

function -h {
cat <<USAGE
 USAGE: demo
USAGE
}; function --help { -h ;}                 # A nice way to handle -h and --help
export LC_ALL=en_US.UTF-8                    # A locale that works consistently

function output_shutdown {
  printf "shutdown!\n"
}

function main {
  printf "oh hai\n"

  trap 'output_shutdown' TERM

  sleep infinity
}

function msg { out "$*" >&2 ;}
function err { local x=$? ; msg "$*" ; return $(( $x == 0 ? 1 : $x )) ;}
function out { printf '%s\n' "$*" ;}

if [[ ${1:-} ]] && declare -F | cut -d' ' -f3 | fgrep -qx -- "${1:-}"
then "$@"
else main "$@"
fi