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

Concept Flow - Integer comparisons (-eq, -ne, -gt, -lt, -ge, -le)

Start

↓

Set two integers

↓

Choose comparison operator

↓

Compare integers

↓

True?

Yes→Execute True branch

↓

Execute False branch

↓

End

This flow shows how bash compares two integers using operators and executes code based on the comparison result.

Execution Sample

Bash Scripting

a=5
b=3
if [ $a -gt $b ]; then
  echo "a is greater"
else
  echo "a is not greater"
fi

This script compares two integers a and b and prints if a is greater than b.

Execution Table

Step	Variable a	Variable b	Condition	Result	Branch Taken	Output
1	5	3	5 -gt 3	True	True branch	a is greater
2	5	3	End of script	-	-	-

💡 Comparison 5 -gt 3 is True, so the True branch runs and script ends after output.

Variable Tracker

Variable	Start	After Step 1	Final
a	unset	5	5
b	unset	3	3

Key Moments - 3 Insights

Why do we use -gt instead of > in bash integer comparisons?

In bash, > is for string comparison or redirection, so integer comparisons use -gt, -lt, etc. as shown in the execution_table step 1.

What happens if variables are not integers?

If variables are not integers, the comparison fails or gives an error because -eq, -ne, -gt, -lt, -ge, -le expect integers, as seen in the condition column.

Why do we use square brackets [ ] around the condition?

Square brackets are a bash syntax for test command to evaluate conditions, as shown in the execution_sample code.

Visual Quiz - 3 Questions

Look at the execution_table step 1, what is the result of the condition '5 -gt 3'?

A False

B True

C Error

D Undefined

💡 Hint

Check the 'Result' column in execution_table row 1.

At which step does the script decide which branch to take?

A Step 2

B Before Step 1

C Step 1

D After Step 2

💡 Hint

Look at the 'Branch Taken' column in execution_table row 1.

If variable a was 2 instead of 5, what would be the output?

A a is not greater

B a is greater

C No output

D Error

💡 Hint

Compare the condition 'a -gt b' with a=2 and b=3 logically.

Concept Snapshot

Bash integer comparisons use operators: -eq (equal), -ne (not equal), -gt (greater than), -lt (less than), -ge (greater or equal), -le (less or equal).
Syntax: [ $a -gt $b ] inside if or test.
Returns true or false to control script flow.
Use only for integers, not strings.
Square brackets [ ] run the test command.
Example: if [ $a -eq $b ]; then ... fi

Full Transcript

This lesson shows how bash scripts compare integers using operators like -eq, -ne, -gt, -lt, -ge, and -le. The script sets two variables a and b, then uses an if statement with [ $a -gt $b ] to check if a is greater than b. If true, it prints 'a is greater'; otherwise, it prints 'a is not greater'. The execution table traces the condition evaluation and branch taken. Key points include using -gt instead of > for integers, square brackets for test, and ensuring variables hold integers. The visual quiz tests understanding of condition results, branch decisions, and output changes if variables change.

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)