ShellCheck for static analysis in Bash Scripting - Step-by-Step Execution

Concept Flow - ShellCheck for static analysis

Write Bash Script

↓

Run ShellCheck

↓

ShellCheck Analyzes Script

↓

Reports Warnings/Errors

↓

Fix Issues in Script

↓

Repeat or Run Script Safely

The flow shows writing a bash script, running ShellCheck to analyze it, getting feedback, fixing issues, and repeating until the script is safe.

Execution Sample

Bash Scripting

echo "$USER"
if [ "$USER" = "root" ]; then
  echo "You are root"
fi

A simple bash script that prints the user and checks if the user is root.

Execution Table

Step	Action	ShellCheck Output	Explanation
1	Analyze script	Line 2: SC2086: Double quote to prevent globbing and word splitting.	ShellCheck warns that $USER should be quoted in the if condition.
2	Analyze script	No other warnings	No other issues found in the script.
3	Fix script	No warnings	After quoting $USER, ShellCheck finds no problems.
4	Run script	Outputs current user and message if root	Script runs safely after fixes.

💡 ShellCheck stops after reporting all issues or confirming no issues.

Variable Tracker

Variable	Start	After Fix	Final
USER	environment variable	unchanged	unchanged

Key Moments - 2 Insights

Why does ShellCheck warn about quoting $USER in the if condition?

ShellCheck warns because unquoted variables can cause unexpected word splitting or globbing, which can break the script. See execution_table step 1 where SC2086 is reported.

What does it mean when ShellCheck reports no warnings after fixing?

It means the script follows best practices and is less likely to have bugs. Refer to execution_table step 3 where no warnings appear after quoting.

Visual Quiz - 3 Questions

Look at the execution table, what warning does ShellCheck give at step 1?

A SC2086: Double quote to prevent globbing and word splitting.

B SC1009: Unexpected token.

C SC2006: Use $(..) instead of backticks.

D No warnings.

💡 Hint

Check the ShellCheck Output column in execution_table row 1.

At which step does ShellCheck report no warnings?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look at the ShellCheck Output column in execution_table rows 2 and 3.

If you forget to fix the quoting issue, what might happen when running the script?

A Script runs perfectly without issues.

B ShellCheck will automatically fix the script.

C Script may fail or behave unexpectedly due to word splitting.

D Script will print an error message and exit.

💡 Hint

Refer to key_moments question 1 and execution_table step 1 explanation.

Concept Snapshot

ShellCheck is a tool to check bash scripts for errors.
Run it on your script to get warnings and suggestions.
Common issue: unquoted variables causing bugs.
Fix issues and rerun ShellCheck until no warnings.
This helps write safer, more reliable scripts.

Full Transcript

ShellCheck is a static analysis tool for bash scripts. You write your script, then run ShellCheck on it. ShellCheck reads your script and looks for common mistakes, like missing quotes around variables. It reports warnings with codes like SC2086. You then fix these issues in your script, for example by adding quotes around variables like $USER. After fixing, you run ShellCheck again to confirm no warnings remain. This process helps you catch bugs early and write safer scripts. The example script prints the current user and checks if it is root. ShellCheck warns about unquoted $USER in the if condition. After quoting it, no warnings remain and the script runs safely.