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Operators in Linux Shell Scripting - Arithmetic, Relational & File Tests

Linux shell programming has the following operators,they compare or evaluate mathematical,logical and relational expression.

1. Arithmetic Operators

Operator	Example	Descriptions
+	$(( a + b ))	Perform Addition
-	$(( a - b ))	Perform Subtraction
*	$(( a * b ))	Perform Multiplication
/	$(( a / b ))	Perform Integer Division
%	$(( a % b ))	Return Remainder (Modulo)
**	$(( a ** b ))	Exponentiation (Power)

Complete Working Arithmetic Script

In Bash, arithmetic expressions can be evaluated cleanly using $(( ... )) or using the legacy expr utility:

#!/bin/bash
# ==========================================================
# Arithmetic Operations in Shell Scripting
# ==========================================================

echo -n "Enter First Number: "
read no1

echo -n "Enter Second Number: "
read no2

# Method 1: Using modern Bash arithmetic expansion $(( ... ))
add=$(( no1 + no2 ))
sub=$(( no1 - no2 ))
mul=$(( no1 * no2 ))
div=$(( no1 / no2 ))
rem=$(( no1 % no2 ))

echo "----------------------------------------"
echo "Addition        ($no1 + $no2) = $add"
echo "Subtraction     ($no1 - $no2) = $sub"
echo "Multiplication  ($no1 * $no2) = $mul"
echo "Division        ($no1 / $no2) = $div"
echo "Remainder       ($no1 % $no2) = $rem"
echo "----------------------------------------"

# Method 2: Floating point division with bc (scale sets decimal precision)
float_div=$(echo "scale=3; $no1 / $no2" | bc)
echo "Precise Decimal Division: $float_div"
						

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2. Relational (Integer Comparison) Operators

Relational operators compare two integer values inside test conditions [ $a -op $b ]:

Operator	Description	Example
-eq	Checks if two numbers are Equal.	[ "$a" -eq "$b" ]
-ne	Checks if two numbers are Not Equal.	[ "$a" -ne "$b" ]
-gt	Checks if left operand is Greater Than right operand.	[ "$a" -gt "$b" ]
-ge	Checks if left operand is Greater Than or Equal to right operand.	[ "$a" -ge "$b" ]
-lt	Checks if left operand is Less Than right operand.	[ "$a" -lt "$b" ]
-le	Checks if left operand is Less Than or Equal to right operand.	[ "$a" -le "$b" ]

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3. String Comparison Operators

Operator	Description	Example
= or ==	Checks if two strings are identical.	[ "$str1" = "$str2" ]
!=	Checks if two strings are not equal.	[ "$str1" != "$str2" ]
-z	True if string length is Zero (empty string).	[ -z "$str1" ]
-n	True if string length is Non-Zero.	[ -n "$str1" ]

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Frequently Asked Questions (FAQ)