Shell script getopt

Ref: https://mug896.github.io/bash-shell/getopts.html

$ script.sh a  b  c  d
     $0     $1 $2 $3 $4
     -------------------
             $@

getopts

The getopts command is a POSIX Shell built-in command that retrieves options and option-arguments from a list of parameters. An option begins with a - (minus sign) followed by a character. An option that does not begin with a - ends parsing. Each time the getopts command is invoked, it places the value of the next option in Name and the index of the next argument to be processed in the shell variable OPTIND. Whenever the shell is invoked, OPTIND is initialized to 1.

getopts <optString> option [parameters="$@"]

echo $option
echo $OPTARG
echo $OPTIND # index of next argument

getopt

The disadvantage of getopts is that it

• only parses short option
• can't parse options after non-option arguments

getopt is a command line utility that parses short and long options and rearranges options and non-option arguments.

getopt -o <shortOptString> -l <longOptString> -- <parameters>

shortOptString

<option1>[:][<option2>[:]...]

When parsing -a -b, shortOptString is ab. If -a option requires an argument, use : as in a:b. getopt parses -a a_arg and -aa_arg in the same way.

Example

set -- -aa_arg -b asdf \
&& getopt -o a:b -- "$@"

 -a 'a_arg' -b -- 'asdf'

longOptString

<option1>[:][,<option2>[:],...]

When parsing --foo --bar, longOptString is foo,bar. If --foo option requires an argument, use : as in foo:,bar. getopt parses --foo=arg and --foo arg in the same way.

Example

set -- --foo arg --bar \
&& getopt -o "" -l foo:,bar -- "$@"

Example script

#!/bin/sh

set -e

RED=$(tput setaf 1)
BOLD=$(tput bold)
DEFAULT=$(tput sgr0)

helpMsg() {
    cat <<END
Usage:
    $(basename "$0") [options] [arguments]

Options:
    -a, --aaa
    -b, --bbb <argument>
    -c, --ccc

Examples:
END
}

if [ $# -eq 0 ] || ! options=$(getopt -o ab:c -l aaa,bbb:,ccc,help \
    -n $(basename "$0") -- "$@"); then
    printf "%sTry '%s --help'\n%s" "${RED}${BOLD}" "$0" "${DEFAULT}" >&2
    exit 1
fi

eval set -- "$options"

while true; do
    case "$1" in
    -a | --aaa)
        echo "$1"
        shift
        ;;
    -b | --bbb)
        echo "$1" "$2"
        shift 2
        ;;
    -c | --ccc)
        echo "$1"
        shift
        ;;
    --help)
        helpMsg
        exit 0
        ;;
    --)
        shift
        break
        ;;
    esac
done

echo "$@"