Bash Basic Operators

There are various operators supported by bash.

Arithmetic operators

Bash does not originally support simple arithmetic operations, but it uses external programs, either awk or expr. Assume variable a holds 10 and variable b holds 20.

Operator	Description	Example
+ (Addition)	Adds values on either side of the operator	expr $a + $b will give 30
- (Subtraction)	Subtracts right hand operand from left hand operand	expr $a - $b will give -10
* (Multiplication)	Multiplies values on either side of the operator	expr $a \* $b will give 200
/ (Division)	Divides left hand operand by right hand operand	expr $b / $a will give 2
% (Modulus)	Divides left hand operand by right hand operand and returns remainder	expr $b % $a will give 0
= (Assignment)	Assigns right operand in left operand	a = $b would assign value of b into a
== (Equality)	Compares two numbers, if both are same then returns true.	[ $a==$b ] would return false.
!= (Not Equality)	Compares two numbers, if both are different then returns true.	[ $a!=$b ] would return true.

Relational operators

Bash support the following relational operators that are specific to numeric values. Assume variable a holds 10 and variable b holds 20.

Operator	Description	Example
-eq	Checks if the value of two operands are equal or not; if yes, then the condition becomes true.	[ $a-eq$b ] is not true.
-ne	Checks if the value of two operands are equal or not; if values are not equal, then the condition becomes true.	[ $a-ne$b ] is true.
-gt	Checks if the value of left operand is greater than the value of right operand; if yes, then the condition becomes true.	[ $a-gt$b ] is not true.
-lt	Checks if the value of left operand is less than the value of right operand; if yes, then the condition becomes true.	[ $a-lt$b ] is true.
-ge	Checks if the value of left operand is greater than or equal to the value of right operand; if yes, then the condition becomes true.	[ $a-ge$b ] is not true.
-le	Checks if the value of left operand is less than or equal to the value of right operand; if yes, then the condition becomes true.	[ $a-le$b ] is true.

Boolean operators

The following Boolean operators are supported by the Bourne Shell. Assume variable a holds 10 and variable b holds 20.

Operator	Description	Example
!	This is logical negation. This inverts a true condition into false and vice versa.	[ ! false ] is true.
-o	This is logical OR. If one of the operands is true, then the condition becomes true.	[ $a-lt20-o$b -gt 100 ] is true.
-a	This is logical AND. If both the operands are true, then the condition becomes true otherwise false.	[ $a-lt20-a$b -gt 100 ] is false.

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