Summary of Linux Shell Operators

Linux Shell Operators

 

Operators in Shell can be divided into arithmetic operators, relational operators, Boolean operators, string operators and file test operators

 

1. Arithmetic operators

 

a=2, b=1

Operator	Description	Example
+	addition	`expr $a + $b` # 3
-	subtraction	`expr $a - $b` # 1
*	multiplication	`expr $a \* $b` # 2, * need to be escaped
/	division	`expr $a / $b' # 2
%	remainder	`expr $a % $b' # 0
=	assign	name=value
==	equality comparison	[ $a == $b ] # false
!=	unequal comparison	[ $a != $b ] # true

 

Note: Conditional expressions should be placed between square brackets and spaces, e.g. [$a==$b] is wrong and must be written as [ $a == $b ]

2. Relational operators

Relational operators only support numbers, not strings, unless the value of the string is a number 

 

a=1, b=2

Operator	Description	Example
-eq	determine whether it is equal	[ $a -eq $b ] # false
-born	are not equal	[$ a -ne $ b] # true
-gt	Is it greater than	[ $a -gt $b ] # false
-lt	Is it less than	[ $a -lt $b ] # true
-give	Is it greater than or equal to	[ $a -ge $b ] # false
-the	Is it less than or equal to	[ $a -le $b ] # true

 

 

3. Boolean Operators

 

Operator	Description	Example
!	NOT operation	[ ! false ] returns true
-O	OR operation	[ true -o false ] returns true
-a	AND operation	[ true -a false] returns false

 

 

4. String operators

 a=abc, b=def

Operator	Description	Example
=	Are they equal	[ $a = $b ] # false
!=	are not equal	[ $a != $b ] # true
-with	length is 0	[ -z $a ] # false
-n	Whether the length is not 0	[ -n $a ] # true
str	is empty	[ $a ] # false

 

 

5. File Test Operator

 

The file test operator is used to detect various attributes of Unix files

 

Operator	Description	Example
-b file	Is it a block device file	[ -b $file ]
-c file	Is it a character device file	[ -c $file ]
-d file	Is it a directory	[ -d $file ]
-f file	Is it a normal file (neither a directory nor a device file)	[ -f $file ]
-g file	Whether the SGID bit is set	[ -g $file ]
-k file	Whether the sticky bit is set (Sticky Bit)	[ -k $file ]
-p file	Is it a named pipe	[ -p $file ]
-in the file	Whether the SUID bit is set	[-u $ file]
-r file	Is it readable	[ -r $file ]
-w file	writable	[ -w $file ]
-x file	Is it executable	[ -x $file ]
-s file	Whether it is not empty (whether the file size is greater than 0), if not empty, return true	[ -s $file ]
-e file	Whether the file (including the directory) exists	[-e $ file]