Integer comparisons (-eq, -ne, -gt, -lt, -ge, -le) in Bash Scripting - Mini Project: Build & Apply

Integer Comparisons in Bash Scripting

📖 Scenario: You are writing a simple bash script to compare two numbers. This is useful when you want to check conditions like if one number is equal to, greater than, or less than another number.

🎯 Goal: Build a bash script that compares two integers using the comparison operators -eq, -ne, -gt, -lt, -ge, and -le. The script will print messages based on these comparisons.

📋 What You'll Learn

Create two integer variables named num1 and num2 with exact values

Create a variable threshold with a specific value

Use if statements with integer comparison operators -eq, -ne, -gt, -lt, -ge, and -le

Print messages that clearly state the comparison results

💡 Why This Matters

🌍 Real World

Integer comparisons are common in scripts that automate tasks like checking system status, validating input, or controlling program flow based on numeric conditions.

💼 Career

Knowing how to compare numbers in bash scripts is essential for system administrators, DevOps engineers, and anyone automating tasks on Linux or Unix systems.

1

Set up two integer variables

Create two integer variables called num1 and num2 with values 10 and 20 respectively.

Bash Scripting

# Create variables num1 and num2 with values 10 and 20
# Your code here

Hint

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

2

Add a threshold variable

Create a variable called threshold and set it to 15.

Bash Scripting

num1=10
num2=20
# Create variable threshold with value 15
# Your code here

Hint

Remember to avoid spaces around the equals sign when assigning values.

3

Compare numbers using integer comparison operators

Write if statements to compare num1 and num2 using -lt and -gt. Print "num1 is less than num2" if num1 is less than num2, otherwise print "num1 is not less than num2".

Bash Scripting

num1=10
num2=20
threshold=15
# Use if statements to compare num1 and num2 with -lt and -gt
# Your code here

Hint

Use square brackets with spaces and double quotes around variables inside the if condition.

4

Print comparison results with all operators

Add if statements to compare num1 and threshold using -eq, -ne, -ge, and -le. Print messages for each comparison result. Finally, print all messages to show the results.

Bash Scripting

num1=10
num2=20
threshold=15
if [ "$num1" -lt "$num2" ]; then
    echo "num1 is less than num2"
else
    echo "num1 is not less than num2"
fi
# Add if statements to compare num1 and threshold with -eq, -ne, -ge, -le
# Print messages for each comparison
# Your code here

Hint

Use separate if blocks for each comparison. Use echo to print messages inside each block.

Practice

1. Which operator checks if two integers are equal in a bash script?

easy

A. -gt

B. -ne

C. -lt

D. -eq

Solution

1. Step 1: Understand the meaning of each operator

   -eq means equal, -ne means not equal, -gt means greater than, -lt means less than.

2. Step 2: Identify the operator for equality

   The operator that checks if two integers are equal is -eq.

3. Final Answer:

   -eq -> Option D

4. Quick Check:

   Equality check = -eq [OK]

Hint: Remember: eq means equal, ne means not equal [OK]

Common Mistakes:

• Confusing -eq with -ne
• Using == instead of -eq in [ ]
• Forgetting spaces around operators

2. Which of the following is the correct syntax to check if variable x is greater than 10 in bash?

easy

A. [ $x > 10 ]

B. [ $x -gt 10 ]

C. [ $x -ge 10 ]

D. [ $x => 10 ]

Solution

1. Step 1: Recall integer comparison operators in bash

   For greater than, bash uses -gt inside [ ]. The symbol > is for string comparison or redirection.

2. Step 2: Check each option

   [ $x -gt 10 ] uses [ $x -gt 10 ] which is correct syntax for integer greater than check.

3. Final Answer:

   [ $x -gt 10 ] -> Option B

4. Quick Check:

   Greater than check uses -gt [OK]

Hint: Use -gt for greater than, not > inside [ ] [OK]

Common Mistakes:

• Using > instead of -gt inside [ ]
• Using => instead of -ge
• Missing spaces around brackets and operators

3. What will be the output of this bash script snippet?

num=5
if [ $num -lt 10 ]; then
echo "Less"
else
echo "More"
fi

medium

A. Less

B. More

C. Syntax Error

D. No output

Solution

1. Step 1: Evaluate the condition [ $num -lt 10 ]

   num is 5, 5 is less than 10, so condition is true.

2. Step 2: Determine which branch runs

   Since condition is true, the then branch runs and prints "Less".

3. Final Answer:

   Less -> Option A

4. Quick Check:

   5 < 10 is true, prints Less [OK]

Hint: If condition true, then branch runs; else runs otherwise [OK]

Common Mistakes:

• Confusing -lt with -le
• Forgetting spaces inside [ ]
• Using > instead of -lt

4. Identify the error in this bash snippet:

count=3
if [ $count -gt 5 ]
then
  echo "High"
fi

medium

A. No error, script runs fine

B. Missing semicolon or newline after condition

C. Missing spaces around brackets

D. Wrong operator -gt used

Solution

1. Step 1: Check if the if condition syntax is correct

   The if condition line ends with ] but the next line is then. Bash requires a newline or semicolon after ] before then.

2. Step 2: Identify the fix

   Add a newline (already present) or a semicolon after ] to separate condition and then. Here newline is present, so syntax is correct.

3. Step 3: Re-examine the snippet

   Actually, the snippet as shown is correct syntax if newline is present after ] before then. If newline missing, error occurs.

4. Final Answer:

   No error, script runs fine -> Option A

5. Quick Check:

   if condition must end with newline or semicolon before then [OK]

Hint: Put newline or semicolon after ] before then [OK]

Common Mistakes:

• Writing if [ condition ] then on same line without semicolon
• Forgetting spaces inside [ ]
• Using > instead of -gt

5. You want to write a bash script that prints "Valid" only if a variable age is between 18 and 30 inclusive. Which condition correctly checks this?

hard

A. [ $age -ge 18 -a $age -le 30 ]

B. [ $age -gt 18 -o $age -lt 30 ]

C. [ $age -ge 18 ] && [ $age -le 30 ]

D. [ $age -gt 18 -a $age -lt 30 ]

Solution

1. Step 1: Understand the range condition

   We want age >= 18 and age <= 30 inclusive, so both conditions must be true.

2. Step 2: Analyze each option

   [ $age -ge 18 -a $age -le 30 ] uses -a inside single [ ], which is valid but less recommended. [ $age -gt 18 -o $age -lt 30 ] uses -o (or), which is wrong. [ $age -ge 18 ] && [ $age -le 30 ] uses two separate [ ] with &&, which is correct and clear. [ $age -gt 18 -a $age -lt 30 ] uses > and < (not inclusive) and -a inside [ ].

3. Final Answer:

   [ $age -ge 18 ] && [ $age -le 30 ] -> Option C

4. Quick Check:

   Use && with separate [ ] for clear inclusive range [OK]

Hint: Use && with separate [ ] for AND conditions [OK]

Common Mistakes:

• Using -o (OR) instead of AND
• Using > and < instead of -ge and -le
• Combining multiple conditions inside one [ ] with -a (less clear)