Friday 19 May 2023

Today I Learned - how to deal with Shell Check SC2086

So, technically I learned this yesterday but 🤷‍♀️

As part of our CI/CD testing, we run shellcheck  against our shell scripts, and saw the following: -

   ^----^ SC2086 (info): Double quote to prevent globbing and word splitting.

for a piece of code that referenced a variable e.g. : -

echo $FILES

The shellcheck Wiki covers this: -

SC2086 – ShellCheck Wiki

and suggests that $FILES be wrapped in double quotes e.g. : -

echo "$FILES"

So far, so good

However, the code in question was actually a variable containing more than one element e.g. : -

FILES="a.txt b.txt c.txt"

so the next line in the script which leveraged the values within the $FILES variable: -

ls "$FILES"

fails with: -

ls: a.txt b.txt c.txt: No such file or directory

Thinking more about this, this kinda made sense i.e. we're treating the values within the $FILES variable as elements within an array, but we're not actually treating the variable as an array, by incrementing through the elements by an index.

The Wiki does reference this: -

Using that as inspiration, I updated the script: -

read -ra files <<<"${FILES}"
ls "${files[@]}"

In essence, this is creating a "real" array from the $FILES variable, and then we're incrementing the index using [@] 

To be clear, I also took inspiration from: -

How to be explicit about intentional word splitting?

and this is my demo / test script: -

#! /bin/bash
# Set variable
FILES="a.txt b.txt c.txt"
echo "Works, but breaks shellcheck"
echo "Fails, but passes shellcheck"
ls "$FILES"
echo "Works, and passes shellcheck"
read -ra files <<<"${FILES}"
ls "${files[@]}"

which, when I run it, does this: -


Works, but breaks shellcheck

a.txt b.txt c.txt

Fails, but passes shellcheck

ls: a.txt b.txt c.txt: No such file or directory

Works, and passes shellcheck

a.txt b.txt c.txt

Finally, for now, there's a great shellcheck plugin for VS Code: -

ShellCheck for Visual Studio Code

and, for the record, the shellcheck project is available on GitHub

No comments:

Visual Studio Code - Wow 🙀

Why did I not know that I can merely hit [cmd] [p]  to bring up a search box allowing me to search my project e.g. a repo cloned from GitHub...