Logical operators (-a, -o, !) in Bash Scripting - Mini Project: Build & Apply

Using Logical Operators in Bash Scripts

📖 Scenario: You are writing a simple bash script to check conditions on numbers, similar to checking if a number is in a certain range or if a file exists. This helps automate decisions in scripts.

🎯 Goal: Build a bash script that uses logical operators -a (and), -o (or), and ! (not) to test multiple conditions together.

📋 What You'll Learn

Create a variable num with the value 15

Create a variable file with the value example.txt

Use if statements with logical operators -a, -o, and !

Print messages based on combined conditions

💡 Why This Matters

🌍 Real World

Logical operators help automate decisions in scripts, like checking if files exist or if values meet certain criteria before running commands.

💼 Career

Understanding bash logical operators is essential for system administrators, DevOps engineers, and anyone automating tasks on Linux or Unix systems.

1

Set up variables

Create a variable called num and set it to 15. Create another variable called file and set it to example.txt.

Bash Scripting

# Create variables num and file
# Your code here

Need a hint?

Use = to assign values without spaces, and quotes for the filename.

2

Add a threshold variable

Create a variable called threshold and set it to 10.

Bash Scripting

num=15
file="example.txt"
# Create variable threshold
# Your code here

Need a hint?

Assign 10 to threshold without spaces.

3

Use logical operators in if statements

Write an if statement that checks if num is greater than threshold -a the file named by file does not exist (use ! and -e). Inside the if, print "Number is big and file missing".

Bash Scripting

num=15
file="example.txt"
threshold=10
# Write if statement with -a and ! -e
# Your code here

Need a hint?

Use [ condition ] with spaces, and combine conditions with -a. Use ! -e "$file" to check file absence.

4

Add an else if with -o operator and print output

Add an elif that checks if num is less than or equal to threshold -o the file named by file exists (use -e). Inside this elif, print "Number is small or file exists". Add an else that prints "No conditions met". Finally, run the script so it prints the output.

Bash Scripting

num=15
file="example.txt"
threshold=10
if [ "$num" -gt "$threshold" -a ! -e "$file" ]; then
    echo "Number is big and file missing"
fi
# Add elif with -o and else with echo
# Your code here

Need a hint?

Use elif [ condition ] with -o for OR. Use else for fallback. Run script to see output.