bash3boilerplate/README.md

• Overview
• Goals
• Features
• Installation
• Changelog
• Best Practices
• Frequently Asked Questions
• Authors
• License

Overview

When hacking up Bash scripts, there are often things such as logging or command-line argument parsing that:

• You need every time
• Come with a number of pitfalls you want to avoid
• Keep you from your actual work

Here's an attempt to bundle those things in a generalized way so that they are reusable as-is in most scripts.

Goals

Delete-Key-Friendly. We propose using main.sh as a base and removing the parts you don't need, rather than introducing packages, includes, compilers, etc. This may feel a bit archaic at first, but that is exactly the strength of Bash scripts that we want to embrace.

Portable. We're targeting Bash 3 (OSX still ships with 3 for instance). If you're going to ask people to install Bash 4 first, you might as well pick a more advanced language as a dependency.

We're automatically testing BASH3 Boilerplate and it's proven to work on:

• Linux GNU bash, version 4.2.25(1)-release (x86_64-pc-linux-gnu)
• OSX GNU bash, version 3.2.51(1)-release (x86_64-apple-darwin13)

Features

• Conventions so that after a while, all your scripts will follow the same, battle-tested structure
• Safe by default (break on error, pipefail, etc)
• Configuration by environment variables
• Simple command-line argument parsing that requires no external dependencies. Definitions are parsed from help info, so there is no duplication
• Helpful magic variables like __file, __dir, and __os
• Logging that supports colors and is compatible with Syslog Severity levels as well as the twelve-factor guidelines

Who uses b3bp?

• Transloadit
• OpenCoarrays
• Sourcery Institute
• Computational Brain Anatomy Laboratory

We're looking for endorsement! Are you also using b3bp? Let us know and get listed.

Installation

There are 3 different ways you can install b3bp:

option 1: Download the main template

Use curl or wget to download the source, save as your script, and start deleting the unwanted bits, and adding your own logic.

wget https://raw.githubusercontent.com/kvz/bash3boilerplate/master/main.sh
vim main.sh

option 2: Clone the entire project

Besides main.sh, this will get you the entire b3bp repository including a few extra functions that we keep in the ./src directory.

git clone git@github.com:kvz/bash3boilerplate.git

option 3: Require via npm

As of v1.0.3, b3bp can also be installed as a Node module so you can define it as a dependency in package.json via:

npm init
npm install --save --save-exact bash3boilerplate

Although this option introduces a Node.js dependency, this does allow for easy version pinning and distribution in environments that already have this prerequisite. But, this is optional and nothing prevents you from ignoring this possibility.

Changelog

Please see the CHANGELOG.md file.

Best practices

As of v1.0.3, b3bp adds some nice re-usable libraries in ./src. In order to make the snippets in ./src more useful, we recommend these guidelines.

Function packaging

It's nice to have a Bash package that can be used in the terminal and also be invoked as a command line function. To achieve this the exporting of your functionality should follow this pattern:

if [ "${BASH_SOURCE[0]}" != "${0}" ]; then
  export -f my_script
else
  my_script "${@}"
  exit $?
fi

This allows a user to source your script or invoke as a script.

# Running as a script
$ ./my_script.sh some args --blah
# Sourcing the script
$ source my_script.sh
$ my_script some more args --blah

(taken from the bpkg project)

Scoping

1. In functions, use local before every variable declaration
2. Use UPPERCASE_VARS to indicate environment variables that can be controlled outside your script
3. Use __double_underscore_prefixed_vars to indicate global variables that are solely controlled inside your script, with the exception of arguments wich are already prefixed with arg_, and functions, over which b3bp poses no restrictions.

Coding style

1. Use two spaces for tabs
2. Use long options (logger --priority vs logger -p). If you're on cli, abbreviations make sense for efficiency. but when you're writing reusable scripts a few extra keystrokes will pay off in readability and avoid ventures into man pages in the future by you or your collaborators. Similarly, we prefer set -o nounset over set -u.
3. Use a single equal sign when checking if [ "${NAME}" = "Kevin" ], double or triple signs are not needed.

Safety and Portability

1. Use {} to enclose your variables in. Otherwise Bash will try to access the $ENVIRONMENT_app variable in /srv/$ENVIRONMENT_app, whereas you probably intended /srv/${ENVIRONMENT}_app. Since it's easy to miss cases like this, we recommend making enclosing a habit.
2. Use set rather than relying on a shebang like #!/usr/bin/env bash -e as that is neutralized when someone runs your script as bash yourscript.sh
3. Use #!/usr/bin/env bash as it is more portable than #!/bin/bash.
4. Use ${BASH_SOURCE[0]} if you refer to current file even if it is sourced by a parent script. Otherwise use ${0}
5. Use :- if you want to test variables that could be undeclared. For instance with if [ "${NAME:-}" = "Kevin" ], $NAME will evaluate to Kevin if the variable is empty. The variable itself will remain unchanged. The syntax to assign a default value is ${NAME:=Kevin}.

Frequently Asked Questions

Please see the FAQ.md file.

Authors

• Kevin van Zonneveld
• Izaak Beekman
• Alexander Rathai
• Dr. Damian Rouson (documentation, feedback)
• @jokajak (documentation)
• Gabriel A. Devenyi (feedback)
• @bravo-kernel (feedback)
• @skanga (feedback)
• galaktos (feedback)

License

Copyright (c) 2013 Kevin van Zonneveld and contributors. Licensed under MIT. You are not obligated to bundle the LICENSE file with your b3bp projects as long as you leave these references intact.