How to show help text if no arguments are passed

Question

I've been using getopts recently and I've set everything up. I've got a problem though. I want it to work so that if someone doesn't enter an argument on the command line, they get the help text, e.g.:

$ ./script
$ help: xyz - argument must be used.

Here's what I have at the moment.

#!/bin/bash

function helptext {
    # ...
}

function mitlicense {
    # ...
}


while getopts "hl" opt; do
  case $opt in
    h) helptext >&2
      exit 1
    ;;
    l) mitlicense >&2
      exit 0
    ;;
    \?) echo "Invalid option: -$OPTARG" >&2
      exit 1
    ;;
    :) echo "Option -$OPTARG requires an argument." >&2
      exit 1
    ;;
    *) helptext >&2
      exit 1
    ;;
  esac
done

Answer 1

Validate user input using an if test such as below.

The -z option of test returns true if the length of the string which follows -z is zero.

 if [ -z "$1" ]
 then
  helptext
  exit 1
 fi