Script testing strategies in Bash Scripting - Mini Project: Build & Apply

Script Testing Strategies

📖 Scenario: You are a system administrator who wrote a small bash script to check disk usage on your server. You want to make sure your script works correctly before using it in daily monitoring.

🎯 Goal: Build a simple bash script that checks disk usage and test it with different inputs to ensure it works as expected.

📋 What You'll Learn

Create a bash script variable with a sample disk usage value

Add a threshold variable to compare disk usage

Write a conditional statement to check if disk usage exceeds the threshold

Print a message indicating if disk usage is safe or critical

💡 Why This Matters

🌍 Real World

System administrators often write scripts to monitor server health. Testing these scripts ensures they behave correctly before deployment.

💼 Career

Knowing how to write and test bash scripts is essential for roles in system administration, DevOps, and automation engineering.

1

Create a variable with disk usage value

Create a bash variable called disk_usage and set it to the value 75 representing disk usage percentage.

Bash Scripting

# Create a variable called disk_usage and set it to 75
# Your code here

Hint

Use variable_name=value syntax without spaces around the equals sign.

2

Add a threshold variable

Create a bash variable called threshold and set it to 80 to represent the critical disk usage percentage.

Bash Scripting

disk_usage=75
# Create a variable called threshold and set it to 80
# Your code here

Hint

Remember to use the same syntax as before for variables.

3

Write a conditional to check disk usage

Write an if statement that compares disk_usage with threshold. If disk_usage is greater than or equal to threshold, set a variable status to "Critical". Otherwise, set status to "Safe".

Bash Scripting

disk_usage=75
threshold=80
# Write an if statement to set status to "Critical" if disk_usage >= threshold, else "Safe"
# Your code here

Hint

Use [ "$disk_usage" -ge "$threshold" ] for numeric comparison in bash.

4

Print the disk usage status

Write a echo command to print the message: Disk usage status: followed by the value of the status variable.

Bash Scripting

disk_usage=75
threshold=80
if [ "$disk_usage" -ge "$threshold" ]; then
    status="Critical"
else
    status="Safe"
fi
# Print the disk usage status message
# Your code here

Hint

Use echo "Disk usage status: $status" to print the message.

Practice

1. Why is it important to test a bash script before using it in real tasks?

easy

A. To reduce the script's file size

B. To make the script run faster automatically

C. To change the script's language to another programming language

D. To find and fix errors early, avoiding bigger problems later

Solution

1. Step 1: Understand the purpose of testing scripts

   Testing helps catch mistakes before the script runs on important data or systems.

2. Step 2: Identify the benefit of early error detection

   Finding errors early prevents failures and saves time and effort in fixing issues later.

3. Final Answer:

   To find and fix errors early, avoiding bigger problems later -> Option D

4. Quick Check:

   Testing = Catch errors early [OK]

Hint: Testing finds errors before damage happens [OK]

Common Mistakes:

• Thinking testing makes scripts faster automatically
• Confusing testing with rewriting code
• Believing testing reduces file size

2. Which command is used to run a bash script with debugging output showing each command executed?

easy

A. bash -e script.sh

B. bash -v script.sh

C. bash -x script.sh

D. bash -c script.sh

Solution

1. Step 1: Recall bash debugging options

   The -x option runs the script showing each command before execution.

2. Step 2: Differentiate from other options

   -v prints shell input lines, -e exits on error, -c runs commands from string.

3. Final Answer:

   bash -x script.sh -> Option C

4. Quick Check:

   Debug with -x = bash -x [OK]

Hint: Use bash -x to see commands run step-by-step [OK]

Common Mistakes:

• Confusing -v with -x for debugging
• Using -e expecting debug output
• Trying -c without command string

3. What will be the output of this script when run with bash -x test.sh?

#!/bin/bash
x=5
if [ $x -gt 3 ]; then
  echo "Greater"
else
  echo "Smaller"
fi

medium

A. + x=5
+ '[' 5 -gt 3 ']'
+ echo 'Greater'
Greater

B. Greater

C. + x=5
+ echo 'Greater'
Greater

D. Smaller

Solution

1. Step 1: Understand bash -x output

   Running with -x prints each command with a plus sign before executing it.

2. Step 2: Trace the script commands

   Commands x=5, the test [ $x -gt 3 ], and echo "Greater" are printed before output.

3. Final Answer:

   + x=5 + '[' 5 -gt 3 ']' + echo 'Greater' Greater -> Option A

4. Quick Check:

   bash -x shows commands with + [OK]

Hint: bash -x shows commands with + before output [OK]

Common Mistakes:

• Ignoring the debug lines starting with +
• Choosing output without debug info
• Confusing else branch output

4. This script is intended to check if a file exists and print a message, but it fails. What is the error?

#!/bin/bash
filename="myfile.txt"
if [ -f $filename ]
then
  echo "File exists"
else
  echo "File missing"
fi

medium

A. The if statement syntax is incorrect; should use double brackets [[ ]]

B. Missing quotes around $filename can cause errors if filename has spaces

C. The script needs to use -e instead of -f to check file existence

D. The echo commands must be inside curly braces { }

Solution

1. Step 1: Identify variable usage in test condition

   The variable $filename is unquoted, which can cause errors if it contains spaces.

2. Step 2: Understand quoting importance in bash tests

   Quoting variables prevents word splitting and errors in test expressions.

3. Final Answer:

   Missing quotes around $filename can cause errors if filename has spaces -> Option B

4. Quick Check:

   Quote variables in tests = Missing quotes around $filename can cause errors if filename has spaces [OK]

Hint: Always quote variables in test conditions [OK]

Common Mistakes:

• Thinking [[ ]] is required instead of [ ]
• Confusing -f and -e options
• Believing echo needs braces

5. You want to test a script that processes user input and exits with code 0 on success or 1 on failure. Which strategy best helps automate testing this behavior?

hard

A. Write test cases that run the script with different inputs and check the exit code using $?

B. Only run the script manually and watch the output on screen

C. Use echo statements inside the script without checking exit codes

D. Rename the script file to .test and run it without arguments

Solution

1. Step 1: Understand exit codes in bash scripts

   Scripts use exit codes to signal success (0) or failure (non-zero).

2. Step 2: Automate testing by running script with inputs and checking $?

   Running script with inputs and verifying $? confirms correct behavior automatically.

3. Final Answer:

   Write test cases that run the script with different inputs and check the exit code using $? -> Option A

4. Quick Check:

   Test exit codes with $? = Write test cases that run the script with different inputs and check the exit code using $? [OK]

Hint: Check $? after running script to verify success/failure [OK]

Common Mistakes:

• Relying only on manual output checks
• Ignoring exit codes in tests
• Assuming renaming files triggers tests