Updated on July 20th, 2021 in #linux

Why You Should Put Braces around Your Variables When Shell Scripting

Braces are often optional but they're almost always worth using for consistency, reducing confusion and using certain features.

Quick Jump: Demo Video

A few years ago I wrote a post about the importance of quoting your variables in Bash and while it touched base on using braces but didn’t go into much detail about them.

This video goes into a few use cases on why I always put braces around my variables. It doesn’t matter if you’re using regular shell, bash, zsh or any other shell interpreter. It’s always worth it.

Demo Video

Examples

Here’s an example script to demonstrate a few things:

#!/usr/bin/env bash

person="Nick"
prefix="cus"
id="abc123"

git_sha="6a18ebb566f1becbbc36545d9038a1452b4aec55"
colors=(red blue green)

cat << EOF
${greeting:-Hey} ${person}, here's a few examples:

Is ${person} cool? $personiscool
Is ${person} cool? ${person}iscool

Database ID: $prefix_id
Database ID: ${prefix}_${id}

Short git SHA: $git_sha:0:8
Short git SHA: ${git_sha:0:8}

What color is the sky? $colors[1]
What color is the sky? ${colors[1]}

All args: ${@}
10th arg: $10
10th arg: ${10}
EOF

Running this with ./example a b c d e f g h i j, produces this output:

Hey Nick, here's a few examples:

Is Nick cool?
Is Nick cool? Nickiscool

Database ID:
Database ID: cus_abc123

Short git SHA: 6a18ebb566f1becbbc36545d9038a1452b4aec55:0:8
Short git SHA: 6a18ebb5

What color is the sky? red[1]
What color is the sky? blue

All args: a b c d e f g h i j
10th arg: a0
10th arg: j

Timestamps

• 0:07 – Quoting your variables is important too
• 0:44 – Taking a look at an example script that demos a few use cases
• 0:54 – Defining a default value
• 1:46 – Help visualize what is part of a variable or a string
• 2:12 – Clearly separating variables when an underscore is involved
• 3:04 – Truncating a variable’s output in Bash
• 3:59 – Reference a specific index in an array
• 4:45 – Being able to reference more than 9 command line arguments
• 5:39 – ShellCheck will call out when you’re not using braces

Reference Links

• https://nickjanetakis.com/blog/linting-and-improving-your-bash-scripts-with-shellcheck

Do you always use braces when shell scripting? Let me know below.