Using getopts to process long and short command line options Ask Question

getopt and getopts are different beasts, and people seem to have a bit of misunderstanding of what they do. getopts is a built-in command to bash to process command-line options in a loop and assign each found option and value in turn to built-in variables, so you can further process them. getopt, however, is an external utility program, and it doesn't actually process your options for you the way that e.g. bash getopts, the Perl Getopt module or the Python optparse/argparse modules do. All that getopt does is canonicalize the options that are passed in — i.e. convert them to a more standard form, so that it's easier for a shell script to process them. For example, an application of getopt might convert the following:

myscript -ab infile.txt -ooutfile.txt

into this:

myscript -a -b -o outfile.txt infile.txt

You have to do the actual processing yourself. You don't have to use getopt at all if you make various restrictions on the way you can specify options:

• only put one option per argument;
• all options go before any positional parameters (i.e. non-option arguments);
• for options with values (e.g. -o above), the value has to go as a separate argument (after a space).

Why use getopt instead of getopts? The basic reason is that only GNU getopt gives you support for long-named command-line options.¹ (GNU getopt is the default on Linux. Mac OS X and FreeBSD come with a basic and not-very-useful getopt, but the GNU version can be installed; see below.)

For example, here's an example of using GNU getopt, from a script of mine called javawrap:

# NOTE: This requires GNU getopt.  On Mac OS X and FreeBSD, you have to install this
# separately; see below.
TEMP=$(getopt -o vdm: --long verbose,debug,memory:,debugfile:,minheap:,maxheap: \
              -n 'javawrap' -- "$@")

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

# Note the quotes around '$TEMP': they are essential!
eval set -- "$TEMP"

VERBOSE=false
DEBUG=false
MEMORY=
DEBUGFILE=
JAVA_MISC_OPT=
while true; do
  case "$1" in
    -v | --verbose ) VERBOSE=true; shift ;;
    -d | --debug ) DEBUG=true; shift ;;
    -m | --memory ) MEMORY="$2"; shift 2 ;;
    --debugfile ) DEBUGFILE="$2"; shift 2 ;;
    --minheap )
      JAVA_MISC_OPT="$JAVA_MISC_OPT -XX:MinHeapFreeRatio=$2"; shift 2 ;;
    --maxheap )
      JAVA_MISC_OPT="$JAVA_MISC_OPT -XX:MaxHeapFreeRatio=$2"; shift 2 ;;
    -- ) shift; break ;;
    * ) break ;;
  esac
done