Argument parsing for Bash

Declare allowed flags/options/arguments, parse, and go.

Requirements:

• Git
• Make
• Bash

Install it in your project

Clone the project into your own project in a reasonable place, e.g., inside $PROJECT_ROOT/vendor/argparse.

Usage

The general pattern of usage goes like this:

• Import this package at the top of your script.
• Declare all allowed flags/options/arguments you want to accept.
• Parse the parameters provided from the command line.
• Use the values in your script.

Import argparse.bash

In your own script, e.g., test.bash source the file:

#!/usr/bin/env bash

. $PROJECT_ROOT/vendor/argparse/libexec/bin/argparse.bash

Declare allowed parameters

Declare any flags/options/arguments you want your program to allow. For instance, to have your program accept --verbose and --fail-fast flags:

flag__id__0="--verbose"
flag__help__0="Display verbose output?"

flag__id__1="--fail-fast"
flag__help__1="Exit on first error?"

The flag__id__X value tells the parser what to look for on the command line, and the flag__help__X value tells the parser what to put in the auto-generated help. The number at the ends (e.g. 0 or 1 in this case) group them together.

Options follow the same pattern:

opt__id__0="--username"
opt__help__0="A username to login with."

opt__id__1="--output"
opt__help__1="A file to write output to."
opt__value__1="out.log"

Note that you can set a default for an option by setting a value (e.g., out.log for opt__value__1).

Positional arguments follow suit:

arg__id__0="identifier"
arg__help__0="A unique identifier/name."

arg__id__1="CIDR"
arg__help__1="A valid CIDR range."

You can also provide a description of the program:

command_description="My little utility."

Parse

Now you can parse the parameters:

parse_args "$@"

This will populate your flags, options, and arguments with values. You can access them like this:

echo "flag 0: $flag__value__0"
echo "opt 0: $opt__value__0"
echo "opt 1: $opt__value__1"
echo "arg 0: $arg__value__0"

Execute your script

Look at the auto-generated help:

bash test.bash --help

Now try calling your script with some parameters:

bash test.bash --verbose --username sally my-thing 10.0.0.0/16

Try forgetting a required parameter:

bash test.bash my-thing

Try leaving off an option's value:

bash test.bash --username

Setup locally

Clone the repo somewhere, e.g.,:

mkdir -p projects
cd projects
git clone https://github.com/jtpaasch/argparse.git

Then go into the repo, and install it:

cd argparse
make install

Tests

To run tests, go into the repo and run this:

make test