Unix in a Nutshell, 4th Edition

Operators

Operators can be one of the following types.

Assignment operators

Operator	Description
=	Assign value.
+= -=	Reassign after addition/subtraction.
*= /= %=	Reassign after multiplication/division/remainder.
&= ^= |=	Reassign after bitwise AND/XOR/OR.
++	Increment.
--	Decrement.

Arithmetic operators

Operator	Description
* / %	Multiplication; integer division; modulus (remainder).
+ -	Addition; subtraction.

Bitwise and logical operators

Operator	Description
~	Binary inversion (one’s complement).
!	Logical negation.
<< >>	Bitwise left shift; bitwise right shift.
&	Bitwise AND.
^	Bitwise exclusive OR.
|	Bitwise OR.
&&	Logical AND (short-circuit).
||	Logical OR (short-circuit).
{ command }	Return 1 if command is successful, 0 otherwise. Note that this is the opposite of command ’s normal return code. The $status variable may be more practical.

Comparison operators

Operator	Description
== !=	Equality; inequality.
<= >=	Less than or equal to; greater than or equal to.
< >	Less than; greater than.
=~	String on left matches a filename pattern on right containing *, ?, or [...].
!~	String on left does not match a filename pattern on right containing *, ?, or [...].

File inquiry operators

Command substitution and filename expansion are performed on file before the test is performed. Operators can be combined (e.g., -ef). The following is a list of the valid file inquiry operators.

Operator