test command and [ ] syntax in Bash Scripting - Mini Project: Build & Apply

Using the test command and [ ] syntax in Bash

📖 Scenario: You are writing a simple Bash script to check if a file exists and if a number is positive. This is common when automating tasks like backups or validations.

🎯 Goal: Build a Bash script that uses the test command and [ ] syntax to check conditions and print messages accordingly.

📋 What You'll Learn

Create a variable with a filename

Create a variable with a number

Use test command to check if the file exists

Use [ ] syntax to check if the number is greater than zero

Print messages based on the checks

💡 Why This Matters

🌍 Real World

Scripts often need to check if files exist before processing them, or validate numbers before calculations.

💼 Career

Knowing how to use <code>test</code> and <code>[ ]</code> is essential for writing reliable Bash scripts in system administration and automation roles.

1

Set up variables for file and number

Create a variable called filename and set it to example.txt. Create another variable called num and set it to 5.

Bash Scripting

# Your code here

Need a hint?

Use = without spaces to assign values in Bash.

2

Check if the file exists using test command

Use the test command to check if the file stored in filename exists. Store the result in an if statement.

Bash Scripting

filename="example.txt"
num=5
# Use test command to check if file exists
# Your code here

Need a hint?

The -e option checks if a file exists.

3

Check if the number is positive using [ ] syntax

Use the [ ] syntax inside an if statement to check if the variable num is greater than zero.

Bash Scripting

filename="example.txt"
num=5
if test -e "$filename"; then
    echo "File exists."
fi
# Use [ ] syntax to check if num is greater than 0
# Your code here

Need a hint?

Use -gt inside [ ] to compare numbers.

4

Print messages based on both checks

Add an else clause to each if statement to print "File does not exist." if the file is missing, and "Number is not positive." if the number is zero or negative. Then run the script to see the output.

Bash Scripting

filename="example.txt"
num=5
if test -e "$filename"; then
    echo "File exists."
else
    # Your code here
fi
if [ "$num" -gt 0 ]; then
    echo "Number is positive."
else
    # Your code here
fi

Need a hint?

Use else to handle the opposite condition in if statements.