Diff for "BashFAQ/101"

How do I process options in a bash script?

For example, how do I code my bash script to accept a bunch of options like

foobar -a --include something

First up, there are some GNU and POSIX standards for how to do this.

do-it-yourself

while "$1"; do
    case "$1" in
        -a|--all) ALL=yes ;shift ;;
        -i|--include) INCLUDE="$2"; shift; shift ;;
        *) echo "$PROG: Bad option '$1', exiting." >&2; exit 1;;
    esac
done

This is all well and good but it's crufty and it doesn't honour the standards - for example, how do you handle concatenation of single-letter options, how about if the user writes -isomething without a space or --include=something?

getopt(1)

TEMP=`getopt -o ab:c:: --long a-long,b-long:,c-long:: -n 'example.bash' -- "$@"`

if [ $? != 0 ] ; then echo "Terminating..." >&2 ; exit 1 ; fi

eval set -- "$TEMP"

while true ; do
        case "$1" in
                -a|--a-long) echo "Option a" ; shift ;;
        .../etc

This is better as it obeys the standards and gives the user a fairly predictable user-interface. There is still the disadvantage that options are coded in at least 2, probably 3 places - in the call to getopt(1), in the case statement that processes them and presumably in the help message that you are going to get around to writing one of these days. This is a classic opportunity for errors to creep in as the code is written and maintained - often not discovered till much, much later.

process-getopt(1)

PROG=$(basename $0)
VERSION='1.2'
USAGE="A tiny example using process-getopt(1)"

# call process-getopt functions to define some options:
source /usr/bin/process-getopt

SLOT=""
SLOT_func()   { [ "${1:-""}" ] && SLOT="yes"; }      # callback for SLOT option
add_opt SLOT "boolean option" s "" slot

TOKEN=""
TOKEN_func()  { [ "${1:-""}" ] && TOKEN="$2"; }      # callback for TOKEN option
add_opt TOKEN "this option takes a value" t n token number

add_std_opts     # define the standard options --help etc:

TEMP=$(call_getopt "$@") || exit 1
eval set -- "$TEMP" # just as with getopt(1)

# remove the options from the command line
process_opts "$@" || shift "$?"

echo "SLOT=$SLOT"
echo "TOKEN=$TOKEN"
echo "args=$@"

Here, all information about each option is defined in once place making for much easier authoring and maintainence. A lot of the dirty work is handled automatically and standards are obeyed as in getopt(1) - because it calls getopt for you. As an added bonus you get a nicely formatted help page (for -h, --help and a starter for a man page (using an easter-egg option  --print-man-page  ).

process-getopt at sourceforge

author's website

Full disclosure: bhepple at freeshell dot org wrote this entry and is the autor of process-getopt(1). Constructive criticism welcome!!

CategoryShell