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about_Operators

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Short description

Describes the operators that are supported by PowerShell.

Long description

An operator is a language element that you can use in a command or expression. PowerShell supports several types of operators to help you manipulate values.

Arithmetic Operators

Use arithmetic operators (+, -, *, /, %) to calculate values in a command or expression. With these operators, you can add, subtract, multiply, or divide values, and calculate the remainder (modulus) of a division operation.

The addition operator concatenates elements. The multiplication operator returns the specified number of copies of each element. You can use arithmetic operators on any .NET type that implements them, such as: Int, String, DateTime, Hashtable, and Arrays.

Bitwise operators (-band, -bor, -bxor, -bnot, -shl, -shr) manipulate the bit patterns in values.

For more information, see about_Arithmetic_Operators.

Assignment Operators

Use assignment operators (=, +=, -=, *=, /=, %=) to assign, change, or append values to variables. You can combine arithmetic operators with assignment to assign the result of the arithmetic operation to a variable.

For more information, see about_Assignment_Operators.

Comparison Operators

Use comparison operators (-eq, -ne, -gt, -lt, -le, -ge) to compare values and test conditions. For example, you can compare two string values to determine whether they're equal.

The comparison operators also include operators that find or replace patterns in text. The (-match, -notmatch, -replace) operators use regular expressions, and (-like, -notlike) use wildcards *.

Containment comparison operators determine whether a test value appears in a reference set (-in, -notin, -contains, -notcontains).

Type comparison operators (-is, -isnot) determine whether an object is of a given type.

For more information, see about_Comparison_Operators.

Logical Operators

Use logical operators (-and, -or, -xor, -not, !) to connect conditional statements into a single complex conditional. For example, you can use a logical -and operator to create an object filter with two different conditions.

For more information, see about_Logical_Operators.

Redirection Operators

Use redirection operators (>, >>, 2>, 2>>, and 2>&1) to send the output of a command or expression to a text file. The redirection operators work like the Out-File cmdlet (without parameters) but they also let you redirect error output to specified files. You can also use the Tee-Object cmdlet to redirect output.

For more information, see about_Redirection

Split and Join Operators

The -split and -join operators divide and combine substrings. The -split operator splits a string into substrings. The -join operator concatenates multiple strings into a single string.

For more information, see about_Split and about_Join.

Type Operators

Use the type operators (-is, -isnot, -as) to find or change the .NET type of an object.

For more information, see about_Type_Operators.

Unary Operators

Use the unary ++ and -- operators to increment or decrement values and - for negation. For example, to increment the variable $a from 9 to 10, you type $a++.

For more information, see about_Arithmetic_Operators.

Special Operators

Special operators have specific use-cases that don't fit into any other operator group. For example, special operators allow you to run commands, change a value's data type, or retrieve elements from an array.

Grouping operator ( )

As in other languages, (...) serves to override operator precedence in expressions. For example: (1 + 2) / 3

However, in PowerShell, there are additional behaviors.

Grouping result expressions

(...) allows you to let output from a command participate in an expression. For example:

PS> (Get-Item *.txt).Count -gt 10
True

Note

Wrapping a command in parentheses causes the automatic variable $? to be set to $true, even when the enclosed command itself set $? to $false. For example, (Get-Item /Nosuch); $? unexpectedly yields True. For more information about $?, see about_Automatic_Variables.

Piping grouped expressions

When used as the first segment of a pipeline, wrapping a command or expression in parentheses invariably causes enumeration of the expression result. If the parentheses wrap a command, it's run to completion with all output collected in memory before the results are sent through the pipeline.

For example, the outputs for these statements are different:

PS> ConvertFrom-Json '["a", "b"]'   | ForEach-Object { "The value is '$_'" }

The value is 'a b'

PS> (ConvertFrom-Json '["a", "b"]') | ForEach-Object { "The value is '$_'" }

The value is 'a'
The value is 'b'

Grouping an expression before piping also ensures that subsequent object-by-object processing can't interfere with the enumeration the command uses to produce its output.

For example, piping the output from Get-ChildItem to Rename-Item can have unexpected effects where an item is renamed, then discovered again and renamed a second time.

Grouping assignment statements

Ungrouped assignment statements don't output values. When grouping an assignment statement, the value of the assigned variable is passed through and can be used in larger expressions. For example:

PS> ($var = 1 + 2)
3
PS> ($var = 1 + 2) -eq 3
True

Wrapping the statement in parentheses turns it into an expression that outputs the value of $var.

This behavior applies to all the assignment operators, including compound operators like +=, and the increment (++) and decrement (--) operators. However, the order of operation for increment and decrement depends on their position.

PS> $i = 0
PS> (++$i) # prefix
1
PS> $i = 0
PS> ($i++) # postfix
0
PS> $i
1

In the prefix case, the value of $i is incremented before being output. In the postfix case, the value of $i is incremented after being output.

You can also use this technique In the context of a conditional statement, such as the if statement.

if ($textFiles = Get-ChildItem *.txt) {
    $textFiles.Count
}

In this example, if no files match, the Get-ChildItem command returns nothing and assigns nothing to $textFiles, which is considered $false in a boolean context. If one or more FileInfo objects are assigned to $textFiles, the conditional evaluates to $true. You can work with the value of $textFiles in the body of the if statement.

Note

While this technique is convenient and concise, it can lead to confusion between the assignment operator (=) and the equality-comparison operator (-eq).

Subexpression operator $( )

Returns the result of one or more statements. For a single result, returns a scalar. For multiple results, returns an array. Use this when you want to use an expression within another expression. For example, to embed the results of command in a string expression.

PS> "Today is $(Get-Date)"
Today is 12/02/2019 13:15:20

PS> "Folder list: $((dir c:\ -dir).Name -join ', ')"
Folder list: Program Files, Program Files (x86), Users, Windows

Array subexpression operator @( )

Returns the result of one or more statements as an array. The result is always an array of 0 or more objects.

PS> $list = @(Get-Process | Select-Object -First 10; Get-Service | Select-Object -First 10 )
PS> $list.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Object[]                                 System.Array

PS> $list.Count
20
PS> $list = @(Get-Service | Where-Object Status -eq Starting )
PS> $list.GetType()

IsPublic IsSerial Name                                     BaseType
-------- -------- ----                                     --------
True     True     Object[]                                 System.Array

PS> $list.Count
0

Hash table literal syntax @{}

Similar to the array subexpression, this syntax is used to declare a hash table. For more information, see about_Hash_Tables.

Call operator &

Runs a command, script, or script block. The call operator, also known as the "invocation operator", lets you run commands that are stored in variables and represented by strings or script blocks. The call operator executes in a child scope. For more about scopes, see about_Scopes.

This example stores a command in a string and executes it using the call operator.

PS> $c = "get-executionpolicy"
PS> $c
get-executionpolicy
PS> & $c
AllSigned

The call operator doesn't parse strings. This means that you can't use command parameters within a string when you use the call operator.

PS> $c = "Get-Service -Name Spooler"
PS> $c
Get-Service -Name Spooler
PS> & $c
& : The term 'Get-Service -Name Spooler' is not recognized as the name of a
cmdlet, function, script file, or operable program. Check the spelling of
the name, or if a path was included, verify that the path is correct and
try again.
At line:1 char:2
+ & $c
+  ~~
    + CategoryInfo          : ObjectNotFound: (Get-Service -Name Spooler:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

The Invoke-Expression cmdlet can execute code that causes parsing errors when using the call operator.

PS> & "1+1"
&: The term '1+1' is not recognized as a name of a cmdlet, function, script
file, or executable program. Check the spelling of the name, or if a path was
included, verify that the path is correct and try again.
At line:1 char:2
+ & "1+1"
+  ~~~~~
    + CategoryInfo          : ObjectNotFound: (1+1:String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException
PS> Invoke-Expression "1+1"
2

You can execute a script using its filename. A script file must have a .ps1 file extension to be executable. Files that have spaces in their path must be enclosed in quotes. If you try to execute the quoted path, PowerShell displays the contents of the quoted string instead of running the script. The call operator allows you to execute the contents of the string containing the filename.

PS C:\Scripts> Get-ChildItem

    Directory: C:\Scripts


Mode                LastWriteTime         Length Name
----                -------------         ------ ----
-a----        8/28/2018   1:36 PM             58 script name with spaces.ps1

PS C:\Scripts> ".\script name with spaces.ps1"
.\script name with spaces.ps1
PS C:\Scripts> & ".\script name with spaces.ps1"
Hello World!

For more about script blocks, see about_Script_Blocks.

Cast operator [ ]

Converts or limits objects to the specified type. If the objects can't be converted, PowerShell generates an error.

[DateTime] '2/20/88' - [DateTime] '1/20/88' -eq [TimeSpan] '31'

A cast can also be performed when a variable is assigned to using cast notation.

Comma operator ,

As a binary operator, the comma creates an array or appends to the array being created. In expression mode, as a unary operator, the comma creates an array with just one member. Place the comma before the member.

$myArray = 1,2,3
$SingleArray = ,1
Write-Output (,1)

Since Write-Output expects an argument, you must put the expression in parentheses.

Dot sourcing operator .

Runs a script in the current scope so that any functions, aliases, and variables that the script creates are added to the current scope, overriding existing ones. Parameters declared by the script become variables. Parameters for which no value has been given become variables with no value. However, the automatic variable $args is preserved.

. c:\scripts\sample.ps1 1 2 -Also:3

Note

The dot sourcing operator is followed by a space. Use the space to distinguish the dot from the dot (.) symbol that represents the current directory.

In the following example, the Sample.ps1 script in the current directory is run in the current scope.

. .\sample.ps1

Format operator -f

Formats strings by using the format method of string objects. Enter the format string on the left side of the operator and the objects to be formatted on the right side of the operator.

"{0} {1,-10} {2:N}" -f 1,"hello",[math]::pi

1 hello      3.14

You can zero-pad a numeric value with the "0" custom specifier. The number of zeroes following the : indicates the maximum width to pad the formatted string to.

"{0:00} {1:000} {2:000000}" -f 7, 24, 365

07 024 000365

If you need to keep the curly braces ({}) in the formatted string, you can escape them by doubling the curly braces.

"{0} vs. {{0}}" -f 'foo'

foo vs. {0}

For more information, see the String.Format method and Composite Formatting.

Index operator [ ]

Selects objects from indexed collections, such as arrays and hash tables. Array indexes are zero-based, so the first object is indexed as [0]. You can also use negative indexes to get the last values. Hash tables are indexed by key value.

Given a list of indices, the index operator returns a list of members corresponding to those indices.

PS> $a = 1, 2, 3
PS> $a[0]
1
PS> $a[-1]
3
PS> $a[2, 1, 0]
3
2
1

(Get-HotFix | Sort-Object installedOn)[-1]

$h = @{key="value"; name="PowerShell"; version="2.0"}
$h["name"]

PowerShell

$x = [xml]"<doc><intro>Once upon a time...</intro></doc>"
$x["doc"]

intro
-----
Once upon a time...

When an object isn't an indexed collection, using the index operator to access the first element returns the object itself. Index values beyond the first element return $null.

PS> (2)[0]
2
PS> (2)[-1]
2
PS> (2)[1] -eq $null
True
PS> (2)[0,0] -eq $null
True

Pipeline operator |

Sends ("pipes") the output of the command that precedes it to the command that follows it. When the output includes more than one object (a "collection"), the pipeline operator sends the objects one at a time.

Get-Process | Get-Member
Get-Service | Where-Object {$_.StartType -eq 'Automatic'}

Range operator ..

The range operator can be used to represent an array of sequential integers. The values joined by the range operator define the start and end values of the range.

1..10
$max = 10
foreach ($a in 1..$max) {Write-Host $a}

You can also create ranges in reverse order.

10..1
5..-5 | ForEach-Object {Write-Output $_}

The start and end values of the range can be any pair of expressions that evaluate to an integer or a character. The endpoints of the range must be convertible to signed 32-bit integers ([int32]). Larger values cause an error. Also, if the range is captured in an array, the size of resulting array is limited to 268435448 (or 256mb - 8). This is maximum size of an array in .NET Framework.

For example, you could use the members of an enumeration for your start and end values.

PS> enum Food {
      Apple
      Banana = 3
      Kiwi = 10
    }
PS> [Food]::Apple..[Food]::Kiwi
0
1
2
3
4
5
6
7
8
9
10

Important

The resulting range isn't limited to the values of the enumeration. Instead it represents the range of values between the two values provided. You can't use the range operator to reliably represent the members of an enumeration.

Member-access operator .

Accesses the properties and methods of an object. The member name may be an expression.

$myProcess.peakWorkingSet
(Get-Process PowerShell).kill()
'OS', 'Platform' | Foreach-Object { $PSVersionTable. $_ }

Starting PowerShell 3.0, when you use the operator on a list collection object that doesn't have the member, PowerShell automatically enumerates the items in that collection and uses the operator on each of them. For more information, see about_Member-Access_Enumeration.

Static member operator ::

Calls the static properties and methods of a .NET class. To find the static properties and methods of an object, use the Static parameter of the Get-Member cmdlet. The member name may be an expression.

[datetime]::Now
'MinValue', 'MaxValue' | Foreach-Object { [int]:: $_ }

See also