An example of how to use getopts in bash

#!/bin/bashusage() { echo "Usage: $0 [-s <45|90>] [-p <string>]" 1>&2; exit 1; }while getopts ":s:p:" o; do    case "${o}" in        s)            s=${OPTARG}            ((s == 45 || s == 90)) || usage            ;;        p)            p=${OPTARG}            ;;        *)            usage            ;;    esacdoneshift $((OPTIND-1))if [ -z "${s}" ] || [ -z "${p}" ]; then    usagefiecho "s = ${s}"echo "p = ${p}"

Example runs:

$ ./myscript.shUsage: ./myscript.sh [-s <45|90>] [-p <string>]$ ./myscript.sh -hUsage: ./myscript.sh [-s <45|90>] [-p <string>]$ ./myscript.sh -s "" -p ""Usage: ./myscript.sh [-s <45|90>] [-p <string>]$ ./myscript.sh -s 10 -p fooUsage: ./myscript.sh [-s <45|90>] [-p <string>]$ ./myscript.sh -s 45 -p foos = 45p = foo$ ./myscript.sh -s 90 -p bars = 90p = bar

The problem with the original code is that:

• h: expects parameter where it shouldn't, so change it into just h (without colon)
• to expect -p any_string, you need to add p: to the argument list

Basically : after the option means it requires the argument.

The basic syntax of getopts is (see: man bash):

getopts OPTSTRING VARNAME [ARGS...]

where:

• OPTSTRING is string with list of expected arguments,

  • h - check for option -h without parameters; gives error on unsupported options;
  • h: - check for option -h with parameter; gives errors on unsupported options;
  • abc - check for options -a, -b, -c; gives errors on unsupported options;

  • :abc - check for options -a, -b, -c; silences errors on unsupported options;

    ^{Notes: In other words, colon in front of options allows you handle the errors in your code. Variable will contain ? in the case of unsupported option, : in the case of missing value.}

• OPTARG - is set to current argument value,

• OPTERR - indicates if Bash should display error messages.

So the code can be:

#!/usr/bin/env bashusage() { echo "$0 usage:" && grep " .)\ #" $0; exit 0; }[ $# -eq 0 ] && usagewhile getopts ":hs:p:" arg; do  case $arg in    p) # Specify p value.      echo "p is ${OPTARG}"      ;;    s) # Specify strength, either 45 or 90.      strength=${OPTARG}      [ $strength -eq 45 -o $strength -eq 90 ] \        && echo "Strength is $strength." \        || echo "Strength needs to be either 45 or 90, $strength found instead."      ;;    h | *) # Display help.      usage      exit 0      ;;  esacdone

Example usage:

$ ./foo.sh ./foo.sh usage:    p) # Specify p value.    s) # Specify strength, either 45 or 90.    h | *) # Display help.$ ./foo.sh -s 123 -p any_stringStrength needs to be either 45 or 90, 123 found instead.p is any_string$ ./foo.sh -s 90 -p any_stringStrength is 90.p is any_string

See: Small getopts tutorial at Bash Hackers Wiki

Use getopt

Why getopt?

To parse elaborated command-line arguments to avoid confusion and clarify the options we are parsing so that reader of the commands can understand what's happening.

What is getopt?

getopt is used to break up (parse) options in command lines for easy parsing by shell procedures, and to check for legal options. It uses the GNU getopt(3) routines to do this.

getopt can have following types of options.

1. No-value options
2. key-value pair options

Note: In this document, during explaining syntax:

• Anything inside [ ] is optional parameter in the syntax/examples.
• is a place holder, which mean it should be substituted with an actual value.

HOW TO USE getopt?

Syntax: First Form

getopt optstring parameters

Examples:

# This is correctgetopt "hv:t::" "-v 123 -t123"  getopt "hv:t::" "-v123 -t123"  # -v and 123 doesn't have whitespace# -h takes no value.getopt "hv:t::" "-h -v123"# This is wrong. after -t can't have whitespace.# Only optional params cannot have whitespace between key and valuegetopt "hv:t::" "-v 123 -t 123"# Multiple arguments that takes value.getopt "h:v:t::g::" "-h abc -v 123 -t21"# Multiple arguments without value# All of these are correctgetopt "hvt" "-htv"getopt "hvt" "-h -t -v"getopt "hvt" "-tv -h"

Here h,v,t are the options and -h -v -t is how options should be given in command-line.

1. 'h' is a no-value option.
2. 'v:' implies that option -v has value andis a mandatory option. ':' means has a value.
3. 't::' implies thatoption -t has value but is optional. '::' means optional.

In optional param, value cannot have whitespace separation with the option. So, in "-t123" example, -t is option 123 is value.

Syntax: Second Form

getopt [getopt_options] [--] [optstring] [parameters]

Here after getopt is split into five parts

• The command itself i.e. getopt
• The getopt_options, it describes how to parse the arguments. single dash long options, double dash options.
• --, separates out the getopt_options from the options you want to parse and the allowed short options
• The short options, is taken immediately after -- is found. Just like the Form first syntax.
• The parameters, these are the options that you have passed into the program. The options you want to parse and get the actual values set on them.

Examples

getopt -l "name:,version::,verbose" -- "n:v::V" "--name=Karthik -version=5.2 -verbose"

Syntax: Third Form

getopt [getopt_options] [-o options] [--] [optstring] [parameters]

Here after getopt is split into five parts

• The command itself i.e. getopt
• The getopt_options, it describes how to parse the arguments. single dash long options, double dash options.
• The short options i.e. -o or --options. Just like the Form first syntax but with option "-o" and before the "--" (double dash).
• --, separates out the getopt_options from the options you want to parse and the allowed short options
• The parameters, these are the options that you have passed into the program. The options you want to parse and get the actual values set on them.

Examples

getopt -l "name:,version::,verbose" -a -o "n:v::V" -- "-name=Karthik -version=5.2 -verbose"

GETOPT_OPTIONS

getopt_options changes the way command-line params are parsed.

Below are some of the getopt_options

Option: -l or --longoptions

Means getopt command should allow multi-character options to be recognised. Multiple options are separated by comma.

For example, --name=Karthik is a long option sent in command line. In getopt, usage of long options are like

getopt "name:,version" "--name=Karthik"

Since name: is specified, the option should contain a value

Option: -a or --alternative

Means getopt command should allow long option to have a single dash '-' rather than double dash '--'.

Example, instead of --name=Karthik you could use just -name=Karthik

getopt "name:,version" "-name=Karthik"

A complete script example with the code:

#!/bin/bash# filename: commandLine.sh# author: @theBuzzyCodershowHelp() {# `cat << EOF` This means that cat should stop reading when EOF is detectedcat << EOF  Usage: ./installer -v <espo-version> [-hrV]Install Pre-requisites for EspoCRM with docker in Development mode-h, -help,          --help                  Display help-v, -espo-version,  --espo-version          Set and Download specific version of EspoCRM-r, -rebuild,       --rebuild               Rebuild php vendor directory using composer and compiled css using grunt-V, -verbose,       --verbose               Run script in verbose mode. Will print out each step of execution.EOF# EOF is found above and hence cat command stops reading. This is equivalent to echo but much neater when printing out.}export version=0export verbose=0export rebuilt=0# $@ is all command line parameters passed to the script.# -o is for short options like -v# -l is for long options with double dash like --version# the comma separates different long options# -a is for long options with single dash like -versionoptions=$(getopt -l "help,version:,verbose,rebuild,dryrun" -o "hv:Vrd" -a -- "$@")# set --:# If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters # are set to the arguments, even if some of them begin with a ‘-’.eval set -- "$options"while truedocase $1 in-h|--help)     showHelp    exit 0    ;;-v|--version)     shift    export version=$1    ;;-V|--verbose)    export verbose=1    set -xv  # Set xtrace and verbose mode.    ;;-r|--rebuild)    export rebuild=1    ;;--)    shift    break;;esacshiftdone

Running this script file:

# With short options grouped together and long option# With double dash '--version'bash commandLine.sh --version=1.0 -rV# With short options grouped together and long option# With single dash '-version'bash commandLine.sh -version=1.0 -rV# OR with short option that takes value, value separated by whitespace# by keybash commandLine.sh -v 1.0 -rV# OR with short option that takes value, value without whitespace# separation from key.bash commandLine.sh -v1.0 -rV# OR Separating individual short optionsbash commandLine.sh -v1.0 -r -V