Section A.2. Operators

A.2. Operators

Operators are used universally for setting, modifying, and comparing information as it passes around the shell.

A.2.1. Arithmetic

The arithmetic operators allow mathematical calculations within the shell. Table A-1 describes the available arithmetic operators and shows how they are used with numbers.

Table A-1. Arithmetic operators

Operator	Description	Example	Result
+	Add two numbers	8+2	10
-	Subtract one number from another Negate a number	82 -8	6 -8
*	Multiply two numbers	8*2	16
/	Divide one number by another	8/2	4
( )	Change calculation order and evaluate the enclosed first	(86)*2	4
%	Remainder of a division (modulus)	8%3	2

When multiple arithmetic operators are combined in a single expression, MSH follows a precedence sequence for evaluation. The unary - operator (negate a number) will always be evaluated first, followed by multiply (*), divide (/), remainder (%), add (+), and subtract (-). Parentheses ((expression)) can be used to override the default operator-evaluation order.

Some arithmetic operators are overloaded for other types. In particular, when strings are used, the add and multiply operators act differently, as shown in Table A-2.

Table A-2. Arithmetic operators on strings

Operator	Description	Example	Result
+	Concatenate two strings	"a"+"b"	"ab"
*	Repeat a string	"c"*6	"cccccc"

A.2.2. Assignment

Assignment operators are used for defining and updating variable values. Although most composite operations are designed for use on numbers, the += and *= operators can also be used on strings.

For the examples in Table A-3, assume that the variable $a has already been assigned a value of 8.

Table A-3. Assignment operators

Operator	Description	Example	Result
=	Set a variable	$a=1	$a is 1
+=	Add to a variable	$a+=3	$a is 11
-=	Subtract from a variable	$a-=2	$a is 6
*=	Multiply a variable	$a*=2	$a is 16
/=	Divide a variable	$a/=2	$a is 4
%=	Set a variable to the remainder of a division	$a%=3	$a is 2
++	Increment a number variable	$a++ ++$a	$a is 9, returns 8 $a is 9, returns 9
	Decrement a number variable	$a $a	$a is 7, returns 8 $a is 7, returns 7

A.2.3. Negation

Monad provides two versions of the unary logical not operator, as shown in Table A-4.

Table A-4. Unary logial not operators

Operator	Description
-not	Logical not
!	Logical not

A.2.4. General Comparison

Comparison operators are frequently used in evaluating test conditions for loops and flow-control statements (see Table A-5).

Table A-5. General comparison operators

Operator	Description
-eq	Equal to
-lt	Less than
-gt	Greater than
-le	Less than or equal to
-ge	Greater than or equal to
-ne	Not equal to
-and	Logical AND
-or	Logical OR

A.2.5. String Comparison

All of the general comparison operators listed in Table A-5 act in a case-insensitive fashion and can be used meaningfully on strings. Table A-6 lists a number of additional string-specific comparison operators.

Table A-6. String operators

Operator	Description
-ieq	Equal to (ignore case)
-ilt	Less than (ignore case)
-igt	Greater than (ignore case)
-ile	Less than or equal to (ignore case)
-ige	Greater than or equal to (ignore case)
-ine	Not equal to (ignore case)
-ceq	Equal to (case-sensitive)
-clt	Less than (case-sensitive)
-cgt	Greater than (case-sensitive)
-cle	Less than or equal to (case-sensitive)
-cge	Greater than or equal to (case-sensitive)
-cne	Not equal to (case-sensitive)
-like	Compare strings by wildcard (ignore case)
-notlike	Compare strings by wildcard (ignore case)
-ilike	Compare strings by wildcard (ignore case)
-inotlike	Compare strings by wildcard (ignore case)
-clike	Compare strings by wildcard (case-sensitive)
-cnotlike	Compare strings by wildcard (case-sensitive)
-match	Compare strings using a regular expression
-notmatch	Compare strings using a regular expression
-imatch	Compare strings using a regular expression (ignore case)
-inotmatch	Compare strings using a regular expression (ignore case)
-cmatch	Compare strings using a regular expression (case-sensitive)
-cnotmatch	Compare strings using a regular expression (case-sensitive)

A.2.6. Array-Containment Operators

Instead of iterating through every element, use array-containment operators to easily determine whether a given array contains a specified element (see Table A-7).

Table A-7. Array containment operators

Operator	Description
-contains	Look for an element in an array
-icontains	Look for an element in an array (case-insensitive)
-ccontains	Look for an element in an array (case-sensitive)

A.2.7. Bitwise Operators

Bitwise operators are commonly used for comparing flags and bit masks (see Table A-8).

Table A-8. Bitwise operators

Operator	Description
-band	Bitwise AND
-bor	Bitwise OR
-bnot	Bitwise NOT