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task.bash

#!/bin/bash

# String with available options (more info: man getopt)
# Colon after argument means that value is required for this argumen
# h -- help
# a -- main args
OPTSTRING="ha:"
VALUE=""

do_work()
{
    local arg="$1"
    # Do whatever you want
    echo "Test: $arg"
    exit 1;
}

print_usage()
{
    echo "USAGE: $0 [ options ]"
    echo "OPTIONS:"
    echo "    -h         Print this message and exit"
    echo "    -a <val>   Option description"

    exit "$1"
}

process_options()
{
    local options_provided="false"
    #  Check that we have some arguments
    if [[ -z "$@" ]]; then
        echo "No options provided!"
        print_usage 1
    fi
    # Parse incoming options
    while getopts "$OPTSTRING" opt; do
        shift $((OPTIND-1))
        case $opt in
            # Usage flag
            h)
                print_usage 0
                ;;
            # Main value flag
            a)
                VALUE=$OPTARG
                ;;
            # Option used without required argument
            :)
                print_usage 1
                ;;
            # Invalid options (optarg manually prints error message)
            *)
                print_usage 1
                ;;
        esac
    done
    # Check for extra arguments
    if [[ -n "$@" ]]; then
        echo "Too many arguments!"
        print_usage 1
    fi
}

# Process incoming options
process_options "$@"
# Do some wotk
do_work "$VALUE"