Integer comparisons (-eq, -ne, -gt, -lt, -ge, -le) in Bash Scripting

Introduction

Integer comparisons help you check if numbers are equal, different, or which one is bigger. This is useful to make decisions in scripts.

Check if a user entered the correct number in a script.

Compare two file sizes to decide which one to keep.

Run a command only if a number is greater than a limit.

Loop until a number reaches a certain value.

Decide what message to show based on a score.

Syntax

Bash Scripting

[ number1 -operator number2 ]

Use spaces around brackets and operators.

Operators: -eq (equal), -ne (not equal), -gt (greater than), -lt (less than), -ge (greater or equal), -le (less or equal).

Examples

Checks if 5 is equal to 5 (true).

Bash Scripting

[ 5 -eq 5 ]

Checks if 3 is not equal to 4 (true).

Bash Scripting

[ 3 -ne 4 ]

Checks if 7 is greater than 2 (true).

Bash Scripting

[ 7 -gt 2 ]

Checks if 1 is less than or equal to 1 (true).

Bash Scripting

[ 1 -le 1 ]

Sample Program

This script compares two numbers and prints if the first is equal, less, or greater than the second.

Bash Scripting

#!/bin/bash

num1=10
num2=20

if [ "$num1" -eq "$num2" ]; then
  echo "$num1 is equal to $num2"
elif [ "$num1" -lt "$num2" ]; then
  echo "$num1 is less than $num2"
else
  echo "$num1 is greater than $num2"
fi

Important Notes

Always put spaces around the brackets and operators, or the comparison will fail.

Use integer comparisons only for whole numbers, not decimals.

For string comparisons, use different operators like = or !=.

Summary

Integer comparisons let you check relationships between numbers in bash scripts.

Use -eq, -ne, -gt, -lt, -ge, and -le inside [ ] with spaces.

They help your script make decisions based on numbers.

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)