getopt vs getopts

Mar 18, 2016 · Comments
code bash

Should you use getopt or getopts in your bash scripts?

The answer can be a bit tricky but mostly straight forward.

getopt

Generally, try to stay away from getopt for the following reasons:

External utility
Traditional versions can’t handle empty argument strings, or arguments with embedded whitespace
For the loops to work perfectly, you must provide the values in the same sequence as the for loop itself; which is very hard to control
Mostly a way to standardize the parameters

The only time I could think of using getopt is when I really want to use a long variable name and there’s just a single one.

Here’a a sample for getopt

#!/bin/bash

#Check the number of arguments. If none are passed, print help and exit.
NUMARGS=$#
# echo -e \\n"Number of arguments: $NUMARGS"
if [ $NUMARGS -eq 0 ]; then
  HELP
fi

OPTS=`getopt -o vhns: --long verbose,dry-run,help,stack-size: -n 'parse-options' -- "$@"`

eval set -- "$OPTS"

while getopt dir:,env: FLAG; do
  case $FLAG in
    -dir)
      DIR=$OPTARG
      echo "-dir used: $OPTARG"
      ;;
    -env)
      PYENV=$OPTARG
      echo "-env used: $OPTARG"
      ;;
    h)  #show help
      HELP
      ;;
    \?) #unrecognized option - show help
      echo -e \\n"Option -${BOLD}$OPTARG${NORM} not allowed."
      HELP
      ;;
  esac
done

shift $((OPTIND-1))  #This tells getopts to move on to the next argument.

getopts

Whereas, getopts is:

Portable and works in any POSIX shell
Lenient with usage of “-a -b” as well as “-ab”
Understands “–” as the option terminator

Here’s a sample for getopts

SCRIPT=`basename ${BASH_SOURCE[0]}`

## Let's do some admin work to find out the variables to be used here
BOLD='\e[1;31m'         # Bold Red
REV='\e[1;32m'       # Bold Green

#Help function
function HELP {
  echo -e "${REV}Basic usage:${OFF} ${BOLD}$SCRIPT -d helloworld ${OFF}"\\n
  echo -e "${REV}The following switches are recognized. $OFF "
  echo -e "${REV}-p ${OFF}  --Sets the environment to use for installing python ${OFF}. Default is ${BOLD} /usr/bin ${OFF}"
  echo -e "${REV}-d ${OFF}  --Sets the directory whose virtualenv is to be setup. Default is ${BOLD} local folder (.) ${OFF}"
  echo -e "${REV}-v ${OFF}  --Sets the python version that you want to install. Default is ${BOLD} 2.7 ${OFF}"
  echo -e "${REV}-h${OFF}  --Displays this help message. No further functions are performed."\\n
  echo -e "Example: ${BOLD}$SCRIPT -d helloworld -p /opt/py27env/bin -v 2.7 ${OFF}"\\n
  exit 1
}

PYENV='/usr/bin'
DIR='.'
VERSION='2.7'

# In case you wanted to check what variables were passed
# echo "flags = $*"

while getopts p:d:v:h FLAG; do
  case $FLAG in
    d)
      DIR=$OPTARG
      ;;
    p)
      PYENV=$OPTARG
      ;;
    v)
      VERSION=$OPTARG
      ;;
    h)
      HELP
      ;;
    \?) #unrecognized option - show help
      echo -e \\n"Option -${BOLD}$OPTARG${OFF} not allowed."
      HELP
      ;;
  esac
done

What if I really wanted long options with getopts?

getopts function can be used to parse long options by putting a dash character followed by a colon into the OPTSPEC. Sharing the solution from this link.

#!/usr/bin/env bash 
OPTSPEC=":hv-:"
while getopts "$OPTSPEC" optchar; do
    case "${optchar}" in
        -)
            case "${OPTARG}" in
                loglevel)
                    val="${!OPTIND}"; OPTIND=$(( $OPTIND + 1 ))
                    echo "Parsing option: '--${OPTARG}', value: '${val}'" >&2;
                    ;;
                loglevel=*)
                    val=${OPTARG#*=}
                    opt=${OPTARG%=$val}
                    echo "Parsing option: '--${opt}', value: '${val}'" >&2
                    ;;
                *)
                    if [ "$OPTERR" = 1 ] && [ "${OPTSPEC:0:1}" != ":" ]; then
                        echo "Unknown option --${OPTARG}" >&2
                    fi
                    ;;
            esac;;
        h)
            echo "usage: $0 [-v] [--loglevel[=]<value>]" >&2
            exit 2
            ;;
        v)
            echo "Parsing option: '-${optchar}'" >&2
            ;;
        *)
            if [ "$OPTERR" != 1 ] || [ "${OPTSPEC:0:1}" = ":" ]; then
                echo "Non-option argument: '-${OPTARG}'" >&2
            fi
            ;;
    esac
done

Coder’s Digest

getopt vs getopts

getopt

getopts

What if I really wanted long options with getopts?