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Operators help us perform various types of operations such as addition, multiplication etc.
There are following types of operators present in bash:
- Arithmetic,
- Relational,
- Boolean,
- File Test,
- String Test
1. Arithmetic Operators
All the arithmetic operators present in bash are discussed below with examples.
These operators work with integers.
1.1 Addition Operator
It’s a + that adds operands together.
Shown in the below example:
1$x=20
2$y=30
3a=`expr $x + $y`
4echo $aThis will display:
50
NOTE:
- The
exprcommand evaluates the expression.- There is
<space>before and after the+operator .
1.2 Subtraction Operator
It’s a - that subtracts second operand from first operand.
Shown in the below example:
1$x=40
2$y=30
3a=`expr $x - $y`
4echo $aThis will display:
10
1.3 Multiplication Operator
It’s a * that multplies operands together.
Shown in the below example:
1$x=2
2$y=3
3a=`expr $x * $y`
4echo $aThis will display:
6
1.4 Division Operator
It’s a / that performs division operation.
Shown in the below example:
-Example 1-
1$x=200
2$y=50
3a=`expr $x / $y`
4echo $aThis will display:
4
-Example 2-
1$x=20
2$y=3
3a=`expr $x / $y`
4echo $aThis will display:
6
1.5 Modulus Operator
It’s a % that performs modulus operation and returns the remainder.
Shown in the below example:
1$x=10
2$y=3
3a=`expr $x % $y`
4echo $aThis will display:
1
1.6 Equality Check Operator
It’s a == that performs equality check operation and returns 1 if both sides are equal otherwise returns 0.
Shown in the below example:
-Example 1-
1$x=10
2$y=10
3a=`expr $x == $y`
4echo $aThis will display:
1
-Example 2-
1$x=10
2$y=5
3a=`expr $x == $y`
4echo $aThis will display:
0
1.7 Not Equal Check Operator
It’s a != that performs equality check operation and returns 0 if both sides are equal otherwise returns 1.
Shown in the below example:
-Example 1-
1$x=10
2$y=10
3a=`expr $x == $y`
4echo $aThis will display:
0
-Example 2-
1$x=10
2$y=5
3a=`expr $x == $y`
4echo $aThis will display:
1
2. Relational Operators
Relational operators are used to perform comparison among given operands.
-eq (Equals to operator)
This checks whether the operands are equal.
This operator is used to perform comparison in the if condition.
1a=10
2b=10
3if [ $a -eq $b ]
4 then
5 echo "Equal"
6else
7 echo "Not Equal"
8fiEqual
-ne (Not equals to operator)
This checks whether the operands are equal.
This operator is used to perform comparison in the if condition.
1a=10
2b=20
3if [ $a -ne $b ]
4 then
5 echo "Not Equal"
6else
7 echo "Equal"
8fiNot Equal
-gt (Greater than operator)
This checks whether the first operand is greater than the second operand.
This operator is used to perform comparison in the if condition.
1a=40
2b=20
3if [ $a -gt $b ]
4 then
5 echo "$a is greater than $b"
6else
7 echo "$a is not greater than $b"
8fi40 is greater than 20
-lt (Less than operator)
This checks whether the first operand is less than the second operand.
This operator is used to perform comparison in the if condition.
1a=20
2b=40
3if [ $a -lt $b ]
4 then
5 echo "$a is less than $b"
6else
7 echo "$a is not less than $b"
8fi20 is greater than 40
-ge (Greater than or equals to operator)
This checks whether the first operand is greater than or equals to the second operand.
This operator is used to perform comparison in the if condition.
1a=40
2b=20
3if [ $a -ge $b ]
4 then
5 echo "$a is greater than or equals to $b"
6else
7 echo "$a is not greater than $b"
8fi40 is greater than or equals to 20
-le (Less than or equals to operator)
This checks whether the first operand is greater than or equals to the second operand.
This operator is used to perform comparison in the if condition.
1a=40
2b=200
3if [ $a -le $b ]
4 then
5 echo "$a is less than or equals to $b"
6else
7 echo "$a is not less than $b"
8fi40 is less than or equals to 200
3. Boolean Operators
! (Not operator)
This changes true into false and vice versa.
We have used this operator in Not equal operator under arithmetic operators.
Shown in the below example:
-Example 1-
1$x=10
2$y=10
3a=`expr $x == $y`
4echo $aThis will display:
0
-Example 2-
1$x=10
2$y=5
3a=`expr $x == $y`
4echo $aThis will display:
1
-o (OR operator)
Checks whether one of the operands is true and executes the statements.
1a=40
2b=20
3c=10
4if [ $a -gt $b -o $c -gt $b]
5 then
6 echo "$a or $c is greater than $b"
7else
8 echo "$a is not less than $b"
9fi40 or 10 is greater than 20
-a (AND operator)
Checks whether all of the operands are true and executes the statements.
1a=40
2b=20
3c=100
4if [ $a -gt $b -a $c -gt $b]
5 then
6 echo "$a and $c are greater than $b"
7else
8 echo "$a is not less than $b"
9fi40 and 100 are greater than 20
4. String Test Operators
These operators are used to perform string related comparisons.
= (Equality Operator)
Check whether two strings are equal.
1user="VIKAS"
2defaultUser="VIKAS"
3if [ $user = $defaultUser ]
4then
5 echo "User is allowed"
6else
7 echo "User is not allowed"
8fiUser is allowed
!= (Not equal operator)
Check whether two strings are not equal.
1user="VIKAS"
2defaultUser="DAVE"
3if [ $user != $defaultUser ]
4then
5 echo "User is not allowed"
6else
7 echo "User is allowed"
8fiUser is not allowed
-z (Zero length string)
Checks whether the string is zero length.
1s=""
2if [ -z $s ]
3then
4 echo "String is zero length"
5else
6 echo "String is non zero length"
7fiString is zero length
-n (Non zero length string)
Checks whether the string is empty.
1s="Village Programmer"
2if [ -n $s ]
3then
4 echo "String is non zero length"
5else
6 echo "String is zero length"
7fiString is non zero length
Empty string check
1s=""
2if [ $s ]
3then
4 echo "String is not empty"
5else
6 echo "String is empty"
7fiString is not empty
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