Use git-rev-parse to do the dirty work for you

parse-with-help-from-git.sh

#!/bin/bash
OPTS_SPEC="\
    $(basename $0 .sh) subcommand <options>

subcommands:

data                 - download a dataset
--
h,help               show help
d,debug              debug output
v,verbose            verbose output
f,file=              input file
 options for data
dataset=             specify dataset to download (eg, 20140219_26816) (default: latest)
g,game-tag=          specify game-tag (default: GAME_TAG env or hc)
"

cmd_data () {
    echo "Hi from the data command"
    echo "INPUT_FILE=$INPUT_FILE"
    echo "DATASET=$DATASET"
    echo "GAME_TAG=$GAME_TAG"
}

parse_args () {
    if [ $# -eq 0 ]; then
        set -- -h
    fi
    eval "$(echo "$OPTS_SPEC" | git rev-parse --parseopt -- "$@" || echo exit $?)"
    cmd=
    while [ $# -gt 0 ]; do
        cmd="$1"
        shift
        case "$cmd" in
            -f|--file) export INPUT_FILE="$1"; shift ;;
            -v|--verbose) export V=1;;
            -d|--debug) export DEBUG=1 ;;
            --dataset) export DATASET="$1"; shift ;;
            -g|--game-tag) export GAME_TAG="$1"; shift ;;
            --) cmd="$1"; shift; break ;;
            -*) echo "Unknown option $cmd" >&2; exit 1 ;;
        esac
    done

    if type -t "cmd_$cmd" > /dev/null; then
        "cmd_$cmd"
    else
        echo "Unknown subcommand: $cmd" >&2
        exit 1
    fi
}

main () {
    parse_args "$@"
}

main "$@"