POSIX-compliant shell script template

template.sh

#!/bin/sh
# unnamedscript

unnamedscript_main() {
	e_args=16
	e_no_realpath=17

	which realpath 2>&1 > /dev/null \
		|| _fatal $e_no_realpath "realpath missing."

  scriptpath="` realpath "$0" `"  
  scriptname="` basename "$scriptpath" `"
  scriptdir="` dirname "$scriptpath" `"
  #rootdir="` dirname "$scriptdir" `"

  while getopts h opt
  do
    case $opt in
      h) unnamedscript_usage && return ;;
      *) _invalid_opt ;;
    esac
  done

  shift ` expr $OPTIND - 1 `

  [ -z "$cmd" ] && cmd="$1"
  shift

  [ -z "$cmd" ] && cmd="help"
  #[ -z "$cmd" ] && cmd="process"

  case "$cmd" in
    #process) "unnamedscript_$cmd" "$@" ;;
    help|usage) unnamedscript_usage ;;
    *) _invalid_cmd ;;
  esac

  return $?
}

#unnamedscript_process() {
#}

unnamedscript_usage() {
cat <<USAGE
Usage: $scriptname [options] command

Available commands:

  help      This help screen.

Available options:

  -h        This help screen.

USAGE
}

_echo() {
  echo "$@"
}

_error() {
  _echo "$@" >&2
}

_fatal() {
	local exitcode
	exitcode="$1"
	shift
	_error "$@"
	exit "$exitcode"
}

_invalid_cmd() {
  _error "Invalid command: $cmd"
  _echo
  unnamedscript_usage
  exit $e_args
}

_invalid_opt() {
  _error "Invalid option: $opt"
  _echo
  unnamedscript_usage
  exit $e_args
}

unnamedscript_main "$@"