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About Operator Precedence

JuanPablo Jofre|Last Updated: 11/17/2016
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2 Contributors

about_Operator_Precedence

SHORT DESCRIPTION

Lists the Windows PowerShell operators in precedence order.

[This topic was contributed by Kirk Munro, a Windows PowerShell MVP from Ottawa, Ontario]

LONG DESCRIPTION

Windows PowerShell operators let you construct simple, but powerful expressions. This topic lists the operators in precedence order. Precedence order is the order in which Windows PowerShell evaluates the operators when multiple operators appear in the same expression.

When operators have equal precedence, Windows PowerShell evaluates them from left to right. The exceptions are the assignment operators, the cast operators, and the negation operators (!, -not, -bnot), which are evaluated from right to left.

You can use enclosures, such as parentheses, to override the standard precedence order and force Windows PowerShell to evaluate the enclosed part of an expression before an unenclosed part.

In the following list, operators are listed in the order that they are evaluated. Operators on the same line, or in the same group, have equal precedence.

The Operator column lists the operators. The Reference column lists the Windows PowerShell Help topic in which the operator is described. To display the topic, type "get-help ".

OPERATOR REFERENCE


$() @() about_Operators

. (dereference) :: (static) about_Operators

[0] (index operator) about_Operators

[int] (cast operators) about_Operators

-split (unary) -join (unary) about_Split, about_Join

, (comma operator) about_Operators

++ -- about_Assignment_Operators

-not ! -bNot about_Logical_Operators, about_Comparison_Operators

.. (range operator) about_Operators

-f (format operator) about_Operators

* / % about_Arithmetic_Operators

+ - about_Arithmetic_Operators

The following group of operators have equal precedence. Their case-sensitive and explicitly case-insensitive variants have the same precedence.

-split (binary) about_Split -join (binary) about_Join -is -isnot -as about_Type_Operators -eq -ne -gt -gt -lt -le about_Comparison_Operators -like -notlike about_comparison_operators -match -notmatch about_comparison_operators -in -notIn about_comparison_operators -contains -notContains about_comparison_operators -replace about_comparison_operators

The list resumes here with the following operators in precedence order:

-band -bor -bxor about_Comparison_Operators

-and -or -xor about_Comparison_Operators

. (dot-source) & (call) about_Scopes, about_Operators

| (pipeline operator) about_Operators

> >> 2> 2>> 2>&1 about_Redirection

= += -= *= /= %= about_Assignment_Operators

EXAMPLES

The following two commands show the arithmetic operators and the effect of using parentheses to force Windows PowerShell to evaluate the enclosed part of the expression first.

C:\PS> 2 + 3 * 4

14


C:\PS> (2 + 3) * 4

20

The following example gets the read-only text files from the local directory and saves them in the $read_only variable.

$read_only = get-childitem *.txt | where-object {$_.isReadOnly}

It is equivalent to the following example.

$read_only = ( get-childitem *.txt | where-object {$_.isReadOnly} )

Because the pipeline operator (|) has a higher precedence than the assignment operator (=), the files that the Get-ChildItem cmdlet gets are sent to the Where-Object cmdlet for filtering before they are assigned to the $read_only variable.

The following example demonstrates that the index operator takes precedence over the cast operator.

The first expression creates an array of three strings. Then, it uses the index operator with a value of 0 to select the first object in the array, which is the first string. Finally, it casts the selected object as a string. In this case, the cast has no effect.

C:\PS> [string]@('Windows','PowerShell','2.0')[0]
Windows

The second expression uses parentheses to force the cast operation to occur before the index selection. As a result, the entire array is cast as a (single) string. Then, the index operator selects the first item in the string array, which is the first character.

C:\PS> ([string]@('Windows','PowerShell','2.0'))[0]
W

In the following example, because the -gt (greater-than) operator has a higher precedence than the -and (logical AND) operator, the result of the expression is FALSE.

C:\PS> 2 -gt 4 -and 1
False

It is equivalent to the following expression.

C:\PS> (2 -gt 4) -and 1
False

If the -and operator had higher precedence, the answer would be TRUE.

C:\PS> 2 -gt (4 -and 1)
True

However, this example demonstrates an important principle of managing operator precedence. When an expression is difficult for people to interpret, use parentheses to force the evaluation order, even when it forces the default operator precedence. The parentheses make your intentions clear to people who are reading and maintaining your scripts.

SEE ALSO

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