Bash Template

Most command-line applications share a common set of features which would be tedious to remember or type out every time you wish to create a new script. Here I collected what are, in my opinion, some best practices for writing new Bash scripts.

Download the Template

Go to the directory where you want to write your new script from and simply copy the template into your directory using one of the commands below.

1. Using wget:

wget https://raw.githubusercontent.com/Animal-Evolution-and-Biodiversity/bash_template/main/template.bash -O template.bash

2. Using curl:

curl https://raw.githubusercontent.com/Animal-Evolution-and-Biodiversity/bash_template/main/template.bash -o template.bash

You can change template.bash into the name of your own script if you would like.

Guidelines

All program should support two standard options: --help and --version. It is also a good idea to provide single-letter alternatives for these: -h and -v. Any output files should prefarably be set using the -o or --output options. If the output is a directory, then it is generally good practice to call it --output-dir. Any program should stop reading command-line options when two dashes -- is specified.

Filetype Extension

Executable (runnable) files can omit the filetype extensions altogether. Libraries or non-executable scripts should use .sh or .bash. I prefer .bash over .sh since .sh may also be used for shell scripts executed by /bin/sh.

Shebang Line

All Bash scripts, or any script really, should start with a shebang line. For Bash, there are two commonly accepted variants:

#!/usr/bin/env bash

or

#!/bin/bash

The first one will choose the first bash in the user's path, while the second one will use the interpreter located in /bin/bash. The bash located in /bin/bash is usually a little older, but it shouldn't matter for non-interactive shells.

All scripts should have a brief explanation of what they do in the first few comment lines like so:

#!/usr/bin/env bash
#
# A minimal Bash template.

Shell Options

These four lines sets a bunch of options which are meant to protect against common problems which may occur:

set -o errtrace
set -o errexit
set -o nounset
set -o pipefail

Below I try to give a brief explanation of every one of these.

• errtrace — inherit signals trapping from functions
• errexit — exit if any command exits with a non-zero exit status
• nounset — exit if an unitialised variabled is used
• pipefail — the script inherits a non-zero exit status from a command within a pipe (|)

See Bash's man page for more details.

Debugging Options

This line adds line numbers and function names to the debugger, when the script is invoked using bash -x bash_template.bash.

export PS4='+ ${LINENO}:${FUNCNAME[0]:-}() '

© Animal Evolution and Biodiversity 2021