Bash argument parsing program template

bash_args_parsing_template

#!/bin/bash

set -o errexit
set -o errtrace
set -o nounset
set -eou pipefail

# ==============================================================================

VERSION="0.1.0"
AUTHOR="Robert W. Pearce"

SCRIPT_NAME="${0##*/}"
VERSION_SHORT="$SCRIPT_NAME version $VERSION"
VERSION_LONG="\
$VERSION_SHORT
Author: $AUTHOR"

bold=$(tput bold)
normal=$(tput sgr0)

HELP="\
This is a helpful description.

${bold}USAGE${normal}
  $SCRIPT_NAME <command> [flags]

${bold}FLAGS${normal}
  -h, -?, --help
    Print the help menu
  -v, --version
    Print version information
  -f <arg>, --foo <arg>
    Pass an argument for foo

${bold}EXAMPLES${normal}
  $ $SCRIPT_NAME -h
  $ $SCRIPT_NAME --version
  $ $SCRIPT_NAME --foo bar
"

# ==============================================================================

function print_help {
  echo "$HELP" # | less -FRX
}

function print_version {
  echo "$VERSION_LONG"
}

function print_error {
  echo "$1" >&2
}

# ==============================================================================

function parse_args {
  if [[ -z "$*" ]]; then
    echo "No arguments provided"
    exit 1
  fi

  # local all_args=("$@")

  while :; do
    local flag="${1:-}"
    local flag_val="${2:-}"

    case "$flag" in
      # Help menu
      -h|-\?|--help)
        print_help
        exit 0
        ;;
      # Version
      -v|--version)
        print_version
        exit 0
        ;;
      # Foo flag
      -f|--foo)
        if [ "$flag_val" ]; then
          echo "--foo value: $flag_val"
          shift # past arg
          shift # past val
        else
          print_error "error: --foo requires a non-empty argument"
          exit 1
        fi
        ;;
      # Foo: handle equals syntax
      --foo=?*)
        local foo_val=${1#*=} # Delete everything up to "=" and assign the remainder
        echo "--foo=?* value is $foo_val"
        shift # past arg
        ;;
      # Foo: handle equals syntax wih no value
      --foo=)
        print_error "error: --foo requires a non-empty argument"
        exit 1
        ;;
      # End of all flags
      --)
        shift # past arg
        shift # past val
        break
        ;;
      # Unknown flag
      -?*)
        # printf "warn: unknown flag (ignored): %s\n" "$flag" >&2
        print_error "warn: unknown flag (ignored): $flag"
        shift # past arg
        ;;
      # Default case, no more options
      *)
        break
        ;;
    esac
  done
}

# ==============================================================================

function main {
  parse_args "$@"
}

main "$@"