Integer comparisons (-eq, -ne, -gt, -lt, -ge, -le) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the -eq operator do in bash scripting?

The -eq operator checks if two integers are equal. It returns true if they are the same number.

beginner

How do you check if two numbers are not equal in bash?

Use the -ne operator. It returns true if the two integers are different.

intermediate

What is the difference between -gt and -ge in bash?

-gt means 'greater than' (strictly bigger), while -ge means 'greater than or equal to' (bigger or the same).

beginner

Write a bash condition to check if variable x is less than 10.

You can write: if [ "$x" -lt 10 ]; then to check if x is less than 10.

intermediate

Why should you use integer comparison operators instead of string comparison for numbers in bash?

Integer operators correctly compare numeric values, while string comparison compares characters and can give wrong results for numbers.

Which operator checks if two integers are equal in bash?

A -eq

B -ne

C -gt

D -lt

The -eq operator tests if two integers are equal.

What does the -ne operator do?

A Checks if two numbers are equal

B Checks if one number is greater than another

C Checks if two numbers are not equal

D Checks if one number is less than another

-ne means 'not equal' for integer comparison.

Which operator means 'greater than or equal to'?

A -gt

B -ge

C -le

D -lt

-ge means 'greater than or equal to'.

How would you check if variable num is less than 5?

A [ "$num" -ne 5 ]

B [ "$num" -gt 5 ]

C [ "$num" -eq 5 ]

D [ "$num" -lt 5 ]

Use -lt to check if a number is less than another.

Why avoid using string comparison operators for numbers in bash?

A They compare characters, not numeric values

B They only work with letters

C They cause syntax errors

D They are slower

String comparison compares characters, which can give wrong results for numbers.

Explain how to compare two integers in bash using the operators -eq, -ne, -gt, -lt, -ge, and -le.

Think about how you check if numbers are equal, not equal, bigger, or smaller.

Describe why integer comparison operators are important in bash scripting and give an example where string comparison would fail.

Consider how numbers behave differently as strings.

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)