ShellCheck for static analysis in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What does ShellCheck report for this script?

Given the following Bash script, what warning or error will ShellCheck produce?

Bash Scripting

echo "User input is: $1"
if [ $1 -eq 10 ]; then
  echo "Input is ten"
fi

A SC1009: The mentioned syntax error was in this if statement.

B No warnings, script is clean.

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

D SC2154: $1 is referenced but not assigned.

💡 Hint

ShellCheck often warns about unquoted variables in test conditions.

ShellCheck warns that $1 should be quoted in the test to avoid word splitting or globbing issues.

📝 Syntax

intermediate

Which script will pass ShellCheck without errors?

Select the Bash script snippet that will NOT produce any ShellCheck warnings or errors.

A for file in *.txt; do echo ${file}; done; echo $file

B for file in *.txt; do echo "$file"; done

C for file in *.txt; do echo ${file}; done

D for file in *.txt; do echo $file; done

💡 Hint

ShellCheck warns about unquoted variables that may cause word splitting.

Option B quotes the variable properly, avoiding word splitting and globbing issues.

🔧 Debug

advanced

Identify the ShellCheck warning for this script

What specific ShellCheck warning will this script produce?

Bash Scripting

#!/bin/bash

read -p "Enter your name: " name
if [ "$name" = "" ]; then
  echo "No name entered"
fi

A SC2143: Use grep -q instead of comparing output with -eq.

B No warnings, script is clean.

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

D SC2162: read without -r will mangle backslashes.

💡 Hint

ShellCheck warns about read command usage without -r option.

ShellCheck recommends using read -r to prevent backslash escapes from being interpreted.

🧠 Conceptual

advanced

Why does ShellCheck warn about this variable usage?

Consider this snippet: filename=$1 if [ -f $filename ]; then echo "File exists" fi Why does ShellCheck warn about the test condition?

A Because $filename is unquoted, it may cause word splitting or globbing issues.

B Because $filename is not declared as a local variable.

C Because -f test requires an absolute path, not a variable.

D Because the if statement syntax is incorrect.

💡 Hint

Think about what happens if the filename contains spaces.

ShellCheck warns that unquoted variables in tests can cause unexpected behavior if the variable contains spaces or special characters.

🚀 Application

expert

What is the output of running ShellCheck on this script?

Given this script: #!/bin/bash for i in {1..3} do echo "Number: $i" done What output will ShellCheck produce?

A No warnings or errors, script is clean.

B SC2034: i appears unused in the loop.

C SC1009: Syntax error near unexpected token '{1..3}'.

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

💡 Hint

Brace expansion is valid in Bash and commonly used in loops.

The script uses valid brace expansion and quotes the variable properly, so ShellCheck reports no issues.

Practice

1. What is the main purpose of using ShellCheck in shell scripting?

easy

A. To find errors and suggest fixes before running the script

B. To execute the script faster

C. To convert shell scripts to Python

D. To add colors to the terminal output

Solution

1. Step 1: Understand what ShellCheck does

   ShellCheck is a tool that analyzes shell scripts without running them to find mistakes.

2. Step 2: Identify the main benefit

   It helps catch errors early, like missing quotes or bad syntax, making scripts safer.

3. Final Answer:

   To find errors and suggest fixes before running the script -> Option A

4. Quick Check:

   ShellCheck finds errors [OK]

Hint: ShellCheck checks scripts for errors before execution [OK]

Common Mistakes:

• Thinking ShellCheck runs the script
• Believing it speeds up script execution
• Confusing it with a code converter

2. Which of the following is the correct way to run ShellCheck on a script named myscript.sh?

easy

A. bash shellcheck myscript.sh

B. checkshell myscript.sh

C. run shellcheck myscript.sh

D. shellcheck myscript.sh

Solution

1. Step 1: Recall the ShellCheck command syntax

   The correct command to run ShellCheck is simply shellcheck followed by the script name.

2. Step 2: Verify the options

   Options B, C, and D use incorrect command names or extra words.

3. Final Answer:

   shellcheck myscript.sh -> Option D

4. Quick Check:

   Use 'shellcheck scriptname' [OK]

Hint: Use 'shellcheck' command followed by script name [OK]

Common Mistakes:

• Typing 'checkshell' instead of 'shellcheck'
• Adding extra words like 'run' before the command
• Using 'bash shellcheck' which is invalid

3. Given this script echo Hello $name and running shellcheck script.sh, what warning will ShellCheck most likely show?

medium

A. SC1000: Syntax error near unexpected token.

B. SC2001: Use 'sed' instead of 'echo'.

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

D. No warnings, script is perfect.

Solution

1. Step 1: Understand ShellCheck's common warnings

   ShellCheck warns when variables are unquoted because it can cause word splitting or globbing.

2. Step 2: Match warning to the script

   The script uses $name without quotes, so ShellCheck will warn about missing quotes (SC2086).

3. Final Answer:

   SC2086: Double quote to prevent globbing and word splitting. -> Option C

4. Quick Check:

   Unquoted variables cause SC2086 warning [OK]

Hint: Look for unquoted variables to spot SC2086 warnings [OK]

Common Mistakes:

• Expecting syntax errors for simple echo
• Thinking no warning appears for unquoted variables
• Confusing warning codes with unrelated messages

4. You have this script snippet:

if [ $count -eq 10 ]; then
echo "Count is 10"
fi

ShellCheck reports an error. What is the best fix?

medium

A. Add quotes around $count: if [ "$count" -eq 10 ]; then

B. Remove the spaces inside [ ]

C. Change -eq to ==

D. Add a semicolon after echo statement

Solution

1. Step 1: Identify the ShellCheck warning cause

   Using $count without quotes can cause errors if $count is empty or contains spaces.

2. Step 2: Apply the fix

   Adding quotes around $count ensures the test works safely even if the variable is empty.

3. Final Answer:

   Add quotes around $count: if [ "$count" -eq 10 ]; then -> Option A

4. Quick Check:

   Quote variables in tests to avoid errors [OK]

Hint: Always quote variables inside [ ] tests [OK]

Common Mistakes:

• Removing spaces inside [ ] which breaks syntax
• Using == instead of -eq for numbers
• Adding unnecessary semicolons

5. You want to write a script that reads a filename from user input and safely prints its contents. Which ShellCheck advice should you follow?

hard

A. Use backticks instead of $( ) for command substitution

B. Always quote variables when using them, e.g., cat "$filename"

C. Avoid quoting variables to allow filename expansion

D. Use eval to run commands with variables

Solution

1. Step 1: Understand safe variable usage

   Quoting variables prevents word splitting and globbing, which can cause errors or security issues.

2. Step 2: Apply ShellCheck best practice

   ShellCheck recommends quoting variables like "$filename" when used in commands like cat.

3. Final Answer:

   Always quote variables when using them, e.g., cat "$filename" -> Option B

4. Quick Check:

   Quote variables to avoid unsafe expansions [OK]

Hint: Quote variables to prevent unsafe expansions [OK]

Common Mistakes:

• Using backticks which are outdated
• Not quoting variables causing errors
• Using eval which can be dangerous