An example showing how to use getopt

gnu_getopt_example.sh

#!/usr/bin/env bash
# Time-stamp: <2017-04-27 09:57:21 kmodi>
# Time-stamp: <2018-03-20 12:58:02 bobpaul>
# derived from kmodi's gist: https://gist.github.com/kaushalmodi/74e9875d5ab0a2bc1010447f1bee5d0a
#
# Example of using getopt to parse command line options
# http://stackoverflow.com/a/29754866/1219634 Limitation: All the options
# starting with - have to be listed in --options/--longoptions, else getopt will
# error out.
# The downside is that if you intend to use this as a wrapper to some other program,
# arguments you want to pass on to that program must come after a -- argument.
# ex: mygrep --myoption mypositional -- -r 'options_for_real_grep' *
getopt --test 2>/dev/null
if [[ $? -ne 4 ]]; then
    echo "GNU's enhanced getopt is required to run this script"
    echo "You can usually find this in the util-linux package"
    echo "On MacOS/OS X see homebrew's package: http://brewformulas.org/Gnu-getopt"
    echo "For anyone else, build from source: http://frodo.looijaard.name/project/getopt"
    exit 1
fi
#bash strict mode: see http://redsymbol.net/articles/unofficial-bash-strict-mode/ for info
set -euo pipefail
IFS=$'\n\t'

# Initialize variables
HELP=0
DEBUG=0
VERBOSE=0
declare -a EXTRA_ARGS
declare -a POSITIONAL
DISCARD_OPTS_AFTER_DOUBLEDASH=0 # 1=Discard, 0=Save opts after -- to ${EXTRA_ARGS}

echo "All pre-getopt arguments: $*"

# An option followed by a single colon ':' means that it *needs* an argument.
# An option followed by double colons '::' means that its argument is optional.
# See `man getopt'.
SHORT=-hDvo:                     # List all the short options
LONG=help,debug,verbose,outfile: # List all the long options

# - Temporarily store output to be able to check for errors.
# - Activate advanced mode getopt quoting e.g. via "--options".
# - Pass arguments only via   -- "$@"   to separate them correctly.
# - getopt auto-adds "--" at the end of ${PARSED}, which is then later set to
#   "$@" using the set command.
if ! PARSED=$(
    getopt --options ${SHORT} \
        --longoptions ${LONG} \
        --name "$0" \
        -- "$@" #Pass all the args to this script to getopt
); then
    # if [[ $? -ne 0 ]]; then
    # e.g. $? == 1
    #  then getopt has complained about wrong arguments to stdout
    exit 2
fi
# Use eval with "$PARSED" to properly handle the quoting
# The set command sets the list of arguments equal to ${PARSED}.
eval set -- "${PARSED}"

echo "Getopt parsed arguments: ${PARSED}"
echo "Effective arguments: $*"
echo "Num args: $#"

dashes=0 #flag to track if we've parsed '--'
while [[ $# -gt 0 ]]; do
    echo "parsing arg: $1"
    case "$1" in
    -o | --outfile)
        shift
        OUT_FILE="$1"
        ;;
    -h | --help) HELP=1 ;;
    -D | --debug) DEBUG=1 ;;
    -v | --verbose) VERBOSE=1 ;;
    --)
        dashes=1
        if [[ ${DISCARD_OPTS_AFTER_DOUBLEDASH} -eq 1 ]]; then break; fi
        ;;
    *) #store positional arguments until we reach the dashes, then store as extra
        if [[ $dashes -eq 0 ]]; then
            POSITIONAL+=("$1")
        else EXTRA_ARGS+=("$1"); fi
        ;;
    esac
    shift # Expose the next argument
done
set -- "${POSITIONAL[@]}"

echo ""
echo ""
echo "Parsed options:"
echo "help: ${HELP}, debug: ${DEBUG}, verbose: ${VERBOSE}, outfile: ${OUT_FILE:-}"

#restore positional arguments as $1, $2, etc
echo "Listing positional arguments:"
while [[ $# -gt 0 ]]; do
    #here's where you can parse your positional arguments
    echo "$1"
    shift
done

echo "Extra arguments: (those after --)"
for i in "${!EXTRA_ARGS[@]}"; do
    #here's the extra args you can pass to a wrapped utility
    echo "${EXTRA_ARGS[$i]}"
done