Bash -lt Operator

The -lt operator in Bash is used to check if the first number is “less than” the second number.

This operator is part of the comparison operators provided by Bash for performing numeric comparisons.

Syntax of -lt Operator

The syntax of -lt operator with the two operands is:

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[ num1 -lt num2 ]

Here, num1 and num2 are the numbers being compared. The condition returns true if num1 is less than num2.

If the first number is less, the condition evaluates to true; otherwise, it evaluates to false.

The -lt operator is commonly used in conditional statements like if and while.

Examples of -lt (Less Than) Operator

Example 1: Checking if a Number is Less Than Another

In this example, we take two predefined numbers and check if the first number is less than the second number using the -lt operator.

Program

check_less.sh

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#!/bin/bash
# Define two numbers
num1=10
num2=15

# Compare the numbers
if [ $num1 -lt $num2 ]; then
  echo "The first number is less."
else
  echo "The first number is not less."
fi

Steps:

  1. Define two numbers: The script initializes two variables, num1 and num2, with values 10 and 15, respectively.
  2. Compare the numbers: The if statement uses the -lt operator to check if the value of num1 is less than num2.
  3. Execute the true condition: If the condition evaluates to true (the first number is less), the script executes the echo command to display the message "The first number is less.".
  4. Execute the false condition: If the condition evaluates to false (the first number is not less), the else block executes, and the script displays the message "The first number is not less.".

Output

The first number is less.

Example 2: Accepting User Input and Comparing Two Numbers

In this example, we will read two numbers from the user and compare them to check if the first number is less than the second.

Program

check_less_input.sh

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#!/bin/bash
# Prompt the user to enter two numbers
echo "Enter the first number:"
read num1
echo "Enter the second number:"
read num2

# Compare the numbers
if [ $num1 -lt $num2 ]; then
  echo "The first number is less."
else
  echo "The first number is not less."
fi

Steps:

  1. Prompt the user to enter the first number: The script displays the message "Enter the first number:" using the echo command and reads the input into the variable num1 using the read command.
  2. Prompt the user to enter the second number: Similarly, the script prompts the user with the message "Enter the second number:" and reads the input into the variable num2.
  3. Once we have the two numbers, we compare them using the -lt operator to check if the first number is less than the second.

Output

Enter the first number:
5
Enter the second number:
10
The first number is less.