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

The following keywords are used by PowerShell workflows:

  Keyword        Reference
  -------------- --------------------
  inlinescript   about_InlineScript
  parallel       about_Parallel
  sequence       about_Sequence
  workflow       about_Workflows

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


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 runtime.

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.

Any number between [int]::MinValue and [int]::MaxValue is allowed.

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.

Any argument that is non-numeric or outside the platform-specific range is
translated to the value of 0.

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> and the script file
terminates with an exit command, the exit code is set to the numeric
argument used with the exit command. If the script has no exit statement,
the exit code is always 0 when the script completes without error or 1 when
the script terminates from an unhandled exception.


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 with a condition.

Syntax:

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


foreach

Defines a loop 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. You can also 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,
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>}


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 it 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 you to indicate which namespaces are used in the session. Type
names, classes, and members require less typing to reference them. You can
also include classes from modules.

Namespace syntax:

    using namespace <.Net-framework-namespace>

Module syntax:

    using module <module-name>

Assembly syntax:

    using assembly <.NET-assembly-path>
    using assembly <.NET-framework-namespace>

For more information, see about_Using.


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