Basic Operators in Shell Scripting

There are 5 basic operators in bash/shell scripting:

• Arithmetic Operators
• Relational Operators
• Boolean Operators
• Bitwise Operators
• File Test Operators

1. Arithmetic Operators: These operators are used to perform normal arithmetics/mathematical operations. There are 7 arithmetic operators:

• Addition (+): Binary operation used to add two operands.
• Subtraction (-): Binary operation used to subtract two operands.
• Multiplication (*): Binary operation used to multiply two operands.
• Division (/): Binary operation used to divide two operands.
• Modulus (%): Binary operation used to find remainder of two operands.
• Increment Operator (++): Unary operator used to increase the value of operand by one.
• Decrement Operator (- -): Unary operator used to decrease the value of a operand by one

#!/bin/bash

# reading data from the user
read -r -p "Enter a: " a

read -r -p "Enter b: " b

add=$((a+b))
echo "Addition of a and b are: "${add}

sub=$((a-b))
echo "Subtraction of a and b are: "${sub}

mul=$((a*b))
echo "Multiplication of a and b are: "${mul}

div=$((a/b))
echo "Division of a and b are: "${div}

mod=$((a%b))
echo "Modulis of a and b are: "${mod}

((++a))
echo "Increment operator when applied on $a results into a :" "${a}"

((--b))
echo "Decrement operator when applied on 'b' results into b :" "${b}"

Output:

2. Relational Operators: Relational operators are those operators which define the relation between two operands. They give either true or false depending upon the relation. They are of 6 types:

• ‘==’ Operator: Double equal to operator compares the two operands. Its returns true is they are equal otherwise returns false.
• ‘!=’ Operator: Not Equal to operator return true if the two operands are not equal otherwise it returns false.
• ‘<‘ Operator: Less than operator returns true if first operand is less than second operand otherwise returns false.
• ‘<=’ Operator: Less than or equal to operator returns true if first operand is less than or equal to second operand otherwise returns false
• ‘>’ Operator: Greater than operator return true if the first operand is greater than the second operand otherwise return false.
• ‘>=’ Operator: Greater than or equal to operator returns true if first operand is greater than or equal to second operand otherwise returns false

#!/bin/bash
 
#reading data from the user
read -p 'Enter a : ' a
read -p 'Enter b : ' b
 
if(( $a==$b ))
then
    echo a is equal to b.
else
    echo a is not equal to b.
fi
 
if(( $a!=$b ))
then
    echo a is not equal to b.
else
    echo a is equal to b.
fi
 
if(( $a<$b ))
then
    echo a is less than b.
else
    echo a is not less than b.
fi
 
if(( $a<=$b ))
then
    echo a is less than or equal to b.
else
    echo a is not less than or equal to b.
fi
 
if(( $a>$b ))
then
    echo a is greater than b.
else
    echo a is not greater than b.
fi
 
if(( $a>=$b ))
then
    echo a is greater than or equal to b.
else
    echo a is not greater than or equal to b.
fi

Output:

3. Logical Operators : They are also known as boolean operators. These are used to perform logical operations. They are of 3 types: 

• Logical AND (&&): This is a binary operator, which returns true if both the operands are true otherwise returns false.
• Logical OR (||): This is a binary operator, which returns true if either of the operands is true or if both the operands are true. It returns false only if both operands are false.
• Not Equal to (!): This is a unary operator which returns true if the operand is false and returns false if the operand is true.

#!/bin/bash

#reading data from the user
read -p 'Enter a : ' a
read -p 'Enter b : ' b

if(($a == "true" & $b == "true" ))
then
    echo Both are true.
else
    echo Both are not true.
fi

if(($a == "true" || $b == "true" ))
then
    echo Atleast one of them is true.
else
    echo None of them is true.
fi

if(( ! $a == "true"  ))
then
    echo "a" was initially false.
else
     echo "a" was initially true.
 fi

Output:

4. Bitwise Operators: A bitwise operator is an operator used to perform bitwise operations on bit patterns. They are of 6 types:

• Bitwise And (&): Bitwise & operator performs binary AND operation bit by bit on the operands.
• Bitwise OR (|): Bitwise | operator performs binary OR operation bit by bit on the operands.
• Bitwise XOR (^): Bitwise ^ operator performs binary XOR operation bit by bit on the operands.
• Bitwise complement (~): Bitwise ~ operator performs binary NOT operation bit by bit on the operand.
• Left Shift (<<): This operator shifts the bits of the left operand to left by number of times specified by right operand.
• Right Shift (>>): This operator shifts the bits of the left operand to right by number of times specified by right operand.

#!/bin/bash

#reading data from the user
read -p 'Enter a : ' a
read -p 'Enter b : ' b

bitwiseAND=$(( a&b ))
echo Bitwise AND of a and b is $bitwiseAND

bitwiseOR=$(( a|b ))
echo Bitwise OR of a and b is $bitwiseOR

bitwiseXOR=$(( a^b ))
echo Bitwise XOR of a and b is $bitwiseXOR

bitiwiseComplement=$(( ~a ))
echo Bitwise Compliment of a is $bitiwiseComplement

leftshift=$(( a<<1 ))
echo Left Shift of a is $leftshift

rightshift=$(( b>>1 ))
echo Right Shift of b is $rightshift

Output:

5. File Test Operator: These operators are used to test a particular property of a file.

• -b operator: This operator check whether a file is a block special file or not. It returns true if the file is a block special file otherwise false.
• -c operator: This operator checks whether a file is a character special file or not. It returns true if it is a character special file otherwise false.
• -d operator: This operator checks if the given directory exists or not. If it exists then operators returns true otherwise false.
• -e operator: This operator checks whether the given file exists or not. If it exits this operator returns true otherwise false.
• -r operator: This operator checks whether the given file has read access or not. If it has read access then it returns true otherwise false.
• -w operator: This operator check whether the given file has write access or not. If it has write then it returns true otherwise false.
• -x operator: This operator check whether the given file has execute access or not. If it has execute access then it returns true otherwise false.
• -s operator: This operator checks the size of the given file. If the size of given file is greater than 0 then it returns true otherwise it is false.

#!/bin/bash

#reading data from the user
read -p 'Enter file name : ' FileName

if [ -e $FileName ]
then
    echo File Exist
else
    echo File doesnot exist
fi

if [ -s $FileName ]
then
    echo The given file is not empty.
else
    echo The given file is empty.
fi

if [ -r $FileName ]
then
    echo The given file has read access.
else
    echo The given file does not has read access.
fi

if [ -w $FileName ]
then
    echo The given file has write access.
else
    echo The given file does not has write access.
fi

if [ -x $FileName ]
then
    echo The given file has execute access.
else
    echo The given file does not has execute access.
fi

Output:

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Article Tags :

• Linux-Unix
• Technical Scripter
• Shell Script