help.sh

#!/bin/bash
# from https://gist.github.com/kovetskiy/a4bb510595b3a6b17bfd1bd9ac8bb4a5#gistcomment-3367404

set -o pipefail

Help=$(cat <<-"HELP"

 my-script — does one thing well

 Usage:
   my-script <input> <output>

 Options:
   <input>   Input file to read.
   <output>  Output file to write. Use '-' for stdout.
   -h        Show this message.

HELP
)

help() {
    echo "$Help"
}

if [[ $# == 0 ]] || [[ "$1" == "-h" ]]; then
    help
    exit 1
fi

echo Hello World