About Language Keywords

SHORT DESCRIPTION

Describes the keywords in the PowerShell scripting language.

LONG DESCRIPTION

PowerShell has the following language keywords. For more information, see the about topic for the keyword and the information that follows the table.

Keyword Reference
Begin about_Functions, about_Functions_Advanced
Break about_Break, about_Trap
Catch about_Try_Catch_Finally
Class about_Classes
Continue about_Continue, about_Trap
Data about_Data_Sections
Define Reserved for future use
Do about_Do, about_While
DynamicParam about_Functions_Advanced_Parameters
Else about_If
Elseif about_If
End about_Functions, about_Functions_Advanced_Methods
Enum about_Enum
Exit Described in this topic
Filter about_Functions
Finally about_Try_Catch_Finally
For about_For
ForEach about_ForEach
From Reserved for future use
Function about_Functions, about_Functions_Advanced
Hidden about_Hidden
If about_If
In about_ForEach
Param about_Functions
Process about_Functions, about_Functions_Advanced
Return about_Return
Static about_Classes
Switch about_Switch
Throw about_Throw, about_Functions_Advanced_Methods
Trap about_Trap, about_Break, about_Try_Catch_Finally
Try about_Try_Catch_Finally
Until about_Do
Using about_Using, about_Classes
Var Reserved for future use
While about_While, about_Do

Language Keywords

Begin

Specifies one part of the body of a function, along with the DynamicParam, Process, and End keywords. The Begin statement list runs one time before any objects are received from the pipeline.

Syntax:

function <name> {
    DynamicParam {<statement list>}
    begin {<statement list>}
    process {<statement list>}
    end {<statement list>}
}

Break

Causes a script to exit a loop.

Syntax:

while (<condition>) {
   <statements>
   ...

   break
   ...

   <statements>
}

Catch

Specifies a statement list to run if an error occurs in the accompanying Try statement list. An error type requires brackets. The second pair of brackets indicates that the error type is optional.

Syntax:

try {<statement list>}
catch [[<error type>]] {<statement list>}

Class

Specifies a new class in PowerShell.

Syntax:

class <class-name> {
    [[hidden] [static] <property-definition> ...]
    [<class-name>([argument-list>]) {<constructor-statement-list>} ...]
    [[hidden] [static] <method-definition> ...]
}

Continue

Causes a script to stop running a loop and to go back to the condition. If the condition is met, the script begins the loop again.

Syntax:

while (<condition>) {
   <statements>
   ...

   continue
   ...

   <statements>
}

Data

In a script, defines a section that isolates data from the script logic. Can also include If statements and some limited commands.

Syntax:

data <variable> [-supportedCommand <cmdlet-name>] {<permitted content>}

Do

Used with the While or Until keyword as a looping construct. PowerShell runs the statement list at least one time, unlike a loop that uses While.

Syntax for While:

do {<statement list>} while (<condition>)

Syntax for Until:

do {<statement list>} until (<condition>)

DynamicParam

Specifies one part of the body of a function, along with the Begin, Process, and End keywords. Dynamic parameters are added at run time.

Syntax:

function <name> {
   DynamicParam {<statement list>}
   begin {<statement list>}
   process {<statement list>}
   end {<statement list>}
}

Else

Used with the If keyword to specify the default statement list.

Syntax:

if (<condition>) {<statement list>}
else {<statement list>}

Elseif

Used with the If and Else keywords to specify additional conditionals. The Else keyword is optional.

Syntax:

if (<condition>) {<statement list>}
elseif (<condition>) {<statement list>}
else {<statement list>}

End

Specifies one part of the body of a function, along with the DynamicParam, Begin, and End keywords. The End statement list runs one time after all the objects have been received from the pipeline.

Syntax:

function <name> {
   DynamicParam {<statement list>}
   begin {<statement list>}
   process {<statement list>}
   end {<statement list>}
}

Enum

enum is used to declare an enumeration; a distinct type that consists of a set of named labels called the enumerator list.

Syntax:

enum <enum-name> {
    <label> [= <int-value>]
    ...
}

Exit

Causes PowerShell to exit a script or a PowerShell instance.

Syntax:

exit
exit <exitcode>

When you use powershell.exe with the File parameter, the .ps1 (script) file itself should include instructions for handling any errors or exceptions that occur while the script is running. You should only use the exit statement to indicate the post-execution status of the script.

In PowerShell, the exit statement sets the value of the $LASTEXITCODE variable. In the Windows Command Shell (cmd.exe), the exit statement sets the value of the %ERRORLEVEL% environment variable.

In the following example, the user sets the error level variable value to 4 by adding exit 4 to the script file test.ps1.

C:\scripts\test>type test.ps1
1

2

3

exit 4

C:\scripts\test>powershell -file ./test.ps1
1

2

3

C:\scripts\test>echo %ERRORLEVEL%
4

When you run powershell.exe -File <path to a script>, the exit statement sets the %ERRORLEVEL% variable to a value other than zero. If you have an unhandled exception in your script, %ERRORLEVEL% is set to the value of 1.

Filter

Specifies a function in which the statement list runs one time for each input object. It has the same effect as a function that contains only a Process block.

Syntax:

filter <name> {<statement list>}

Finally

Defines a statement list that runs after statements that are associated with Try and Catch. A Finally statement list runs even if you press CTRL+C to leave a script or if you use the Exit keyword in the script.

Syntax:

try {<statement list>}
catch [<error type>] {<statement list>}
finally {<statement list>}

For

Defines a loop by using a condition.

Syntax:

for (<initialize>; <condition>; <iterate>) { <statement list> }

ForEach

Defines a loop by using each member of a collection.

Syntax:

ForEach (<item> in <collection>) { <statement list> }

From

Reserved for future use.

Function

Creates a named statement list of reusable code. You can name the scope a function belongs to. And, you can specify one or more named parameters by using the Param keyword. Within the function statement list, you can include DynamicParam, Begin, Process, and End statement lists.

Syntax:

function [<scope:>]<name> {
   param ([type]<$pname1> [, [type]<$pname2>])
   DynamicParam {<statement list>}
   begin {<statement list>}
   process {<statement list>}
   end {<statement list>}
}

You also have the option of defining one or more parameters outside the statement list after the function name.

Syntax:

function [<scope:>]<name> [([type]<$pname1>, [[type]<$pname2>])] {
   DynamicParam {<statement list>}
   begin {<statement list>}
   process {<statement list>}
   end {<statement list>}
}

If

Defines a conditional.

Syntax:

if (<condition>) {<statement list>}

Hidden

Hides class members from the default results of the Get-Member cmdlet, and from IntelliSense and tab completion results.

Syntax:

Hidden [data type] $member_name

In

Used in a ForEach statement to create a loop that uses each member of a collection.

Syntax:

ForEach (<item> in <collection>){<statement list>}

InlineScript

Runs workflow commands in a shared PowerShell session. This keyword is valid only in a PowerShell Workflow.

Syntax:

workflow <verb>-<noun>
{
   InlineScript
   {
      <Command/Expression>
      ...

   }
}

The InlineScript keyword indicates an InlineScript activity, which runs commands in a shared standard (non-workflow) session. You can use the InlineScript keyword to run commands that are not otherwise valid in a workflow, and to run commands that share data. By default, the commands in an InlineScript script block run in a separate process.

For more information, see Running PowerShell Commands in a Workflow.

Param

Defines the parameters in a function.

Syntax:

function [<scope:>]<name> {
   param ([type]<$pname1>[, [[type]<$pname2>]])
   <statement list>
}

Process

Specifies a part of the body of a function, along with the DynamicParam, Begin, and End keywords. When a Process statement list receives input from the pipeline, the Process statement list runs one time for each element from the pipeline. If the pipeline provides no objects, the Process statement list does not run. If the command is the first command in the pipeline, the Process statement list runs one time.

Syntax:

function <name> {
   DynamicParam {<statement list>}
   begin {<statement list>}
   process {<statement list>}
   end {<statement list>}
}

Return

Causes PowerShell to leave the current scope, such as a script or function, and writes the optional expression to the output.

Syntax:

return [<expression>]

Static

Specifies the property or method defined is common to all instances of the class in which is defined.

See Class for usage examples.

Switch

To check multiple conditions, use a Switch statement. The Switch statement is equivalent to a series of If statements, but it is simpler.

The Switch statement lists each condition and an optional action. If a condition obtains, the action is performed.

Syntax 1:

switch [-regex|-wildcard|-exact][-casesensitive] ( <value> )
{
   <string>|<number>|<variable>|{ <expression> } {<statement list>}
   <string>|<number>|<variable>|{ <expression> } {<statement list>}
   ...

   default {<statement list>}
}

Syntax 2:

switch [-regex|-wildcard|-exact][-casesensitive] -file <filename>
{
   <string>|<number>|<variable>|{ <expression> } {<statement list>}
   <string>|<number>|<variable>|{ <expression> } {<statement list>}
   ...

   default {<statement list>}
}

Throw

Throws an object as an error.

Syntax:

throw [<object>]

Trap

Defines a statement list to be run if an error is encountered. An error type requires brackets. The second pair of brackets indicates that the error type is optional.

Syntax:

trap [[<error type>]] {<statement list>}

Try

Defines a statement list to be checked for errors while the statements run. If an error occurs, PowerShell continues running in a Catch or Finally statement. An error type requires brackets. The second pair of brackets indicates that the error type is optional.

Syntax:

try {<statement list>}
catch [[<error type>]] {<statement list>}
finally {<statement list>}

Until

Used in a Do statement as a looping construct where the statement list is executed at least one time.

Syntax:

do {<statement list>} until (<condition>)

Using

Allows to indicate which namespaces are used in the session. Classes and members require less typing to mention them. You can also include classes from modules.

Syntax #1:

using namespace <.Net-framework-namespace>

Syntax #2:

using module <module-name>

While

The while statement is a looping construct where the condition is tested before the statements are executed. If the condition is FALSE, then the statements do not execute.

Statement syntax:

while (<condition>) {
   <statements>
 }

When used in a Do statement, while is part of a looping construct where the statement list is executed at least one time.

Do loop Syntax:

do {<statement list>} while (<condition>)

SEE ALSO