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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
InlineScript about_InlineScript
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
- about_Special_Characters
- about_Wildcards