Use Python's argparse module in shell scripts

The function argparse parses its arguments using argparse.ArgumentParser. The command line options are defined in the function's stdin. argparse.bash should be in the same directory as a script that uses it.

Python 2.6+ or 3.2+ is required. See https://docs.python.org/2.7/library/argparse.html for a description of the python module. Note that some of the Python module's features won't work as expected (or at all) in this simplistic implementation.

Get argparse.bash:

wget https://raw.githubusercontent.com/nhoffman/argparse-bash/master/argparse.bash
chmod +x argparse.bash

Then move the file into the same directory as any scripts that will use it.

Alternatively, you can paste the body of the argparse() function into your script (in which case you would of course omit the line sourcing argparse.bash in the examples below).

Here's an example, example.sh:

#!/bin/bash

source $(dirname $0)/argparse.bash || exit 1
argparse "$@" <<EOF || exit 1
parser.add_argument('infile')
parser.add_argument('outfile')
parser.add_argument('-a', '--the-answer', default=42, type=int,
                    help='Pick a number [default %(default)s]')
parser.add_argument('-d', '--do-the-thing', action='store_true',
                    default=False, help='store a boolean [default %(default)s]')
parser.add_argument('-m', '--multiple', nargs='+',
                    help='multiple values allowed')
EOF

echo required infile: "$INFILE"
echo required outfile: "$OUTFILE"
echo the answer: "$THE_ANSWER"
echo -n do the thing?
if [[ $DO_THE_THING ]]; then
    echo " yes, do it"
else
    echo " no, do not do it"
fi
echo -n "arg with multiple values: "
for a in "${MULTIPLE[@]}"; do
    echo -n "[$a] "
done
echo

Example output of this script:

$ ./example.sh infile.txt "name with spaces.txt"
required infile: infile.txt
required outfile: name with spaces.txt
the answer: 42
do the thing? no, do not do it
arg with multiple values: []

Note that hyphens in the long option names are changed to underscores, and variables are all-caps (to be more bash-y).

Help text looks like this:

$ ./example.sh -h
usage: example.sh [-h] [-a THE_ANSWER] [-d] [-m MULTIPLE [MULTIPLE ...]]
                  infile outfile

positional arguments:
  infile
  outfile

optional arguments:
  -h, --help            show this help message and exit
  -a THE_ANSWER, --the-answer THE_ANSWER
                        Pick a number [default 42]
  -d, --do-the-thing    store a boolean [default False]
  -m MULTIPLE [MULTIPLE ...], --multiple MULTIPLE [MULTIPLE ...]
                        multiple values allowed

Error messages:

$ ./example.sh foo
usage: example.sh [-h] [-a THE_ANSWER] [-d] [-m MULTIPLE [MULTIPLE ...]]
                  infile outfile
example.sh: error: too few arguments
$ ./example.sh foo bar -n baz
usage: example.sh [-h] [-a THE_ANSWER] [-d] [-m MULTIPLE [MULTIPLE ...]]
                  infile outfile
example.sh: error: unrecognized arguments: -n baz

Executing argparse.bash (as opposed to sourcing it) prints a script template to stdout:

$ ./argparse.bash
#!/bin/bash

source $(dirname $0)/argparse.bash || exit 1
argparse "$@" <<EOF || exit 1
parser.add_argument('infile')
parser.add_argument('-o', '--outfile')

EOF

echo "INFILE: ${INFILE}"
echo "OUTFILE: ${OUTFILE}"

A few notes:

• action=store_true or store_false provides a value of "yes" for True, "" for False
• args='+' or args='*' provides an array of values.

MIT License (see LICENSE.txt)

Copyright (c) 2017 Noah Hoffman