about_Scripts

Short description

Describes how to run and write scripts in PowerShell.

Long description

A script is a plain text file that contains one or more PowerShell commands. PowerShell scripts have a .ps1 file extension.

Running a script is a lot like running a cmdlet. You type the path and file name of the script and use parameters to submit data and set options. You can run scripts on your computer or in a remote session on a different computer.

Writing a script saves a command for later use and makes it easy to share with others. Most importantly, it lets you run the commands simply by typing the script path and the filename. Scripts can be as simple as a single command in a file or as extensive as a complex program.

Scripts have additional features, such as the #Requires special comment, the use of parameters, support for data sections, and digital signing for security. You can also write Help topics for scripts and for any functions in the script.

How to run a script

Before you can run a script on Windows, you need to change the default PowerShell execution policy. Execution policy does not apply to PowerShell running on non-Windows platforms.

The default execution policy, Restricted, prevents all scripts from running, including scripts that you write on the local computer. For more information, see about_Execution_Policies.

The execution policy is saved in the registry, so you need to change it only once on each computer.

To change the execution policy, use the following procedure.

At the command prompt, type:

Set-ExecutionPolicy AllSigned

or

Set-ExecutionPolicy RemoteSigned

The change is effective immediately.

To run a script, type the full name and the full path to the script file.

For example, to run the Get-ServiceLog.ps1 script in the C:\Scripts directory, type:

C:\Scripts\Get-ServiceLog.ps1

To run a script in the current directory, type the path to the current directory, or use a dot to represent the current directory, followed by a path backslash (.\).

For example, to run the ServicesLog.ps1 script in the local directory, type:

.\Get-ServiceLog.ps1

If the script has parameters, type the parameters and parameter values after the script filename.

For example, the following command uses the ServiceName parameter of the Get-ServiceLog script to request a log of WinRM service activity.

.\Get-ServiceLog.ps1 -ServiceName WinRM

As a security feature, PowerShell does not run scripts when you double-click the script icon in File Explorer or when you type the script name without a full path, even when the script is in the current directory. For more information about running commands and scripts in PowerShell, see about_Command_Precedence.

Run with PowerShell

Beginning in PowerShell 3.0, you can run scripts from File Explorer.

To use the "Run with PowerShell" feature:

Run File Explorer, right-click the script filename and then select "Run with PowerShell".

The "Run with PowerShell" feature is designed to run scripts that do not have required parameters and do not return output to the command prompt.

For more information, see about_Run_With_PowerShell.

Running scripts on other computers

To run a script on one or more remote computers, use the FilePath parameter of the Invoke-Command cmdlet.

Enter the path and filename of the script as the value of the FilePath parameter. The script must reside on the local computer or in a directory that the local computer can access.

The following command runs the Get-ServiceLog.ps1 script on the remote computers named Server01 and Server02.

Invoke-Command -ComputerName Server01,Server02 -FilePath `
  C:\Scripts\Get-ServiceLog.ps1

Get help for scripts

The Get-Help cmdlet gets the help topics for scripts as well as for cmdlets and other types of commands. To get the help topic for a script, type Get-Help followed by the path and filename of the script. If the script path is in your Path environment variable, you can omit the path.

For example, to get help for the ServicesLog.ps1 script, type:

get-help C:\admin\scripts\ServicesLog.ps1

How to write a script

A script can contain any valid PowerShell commands, including single commands, commands that use the pipeline, functions, and control structures such as If statements and For loops.

To write a script, open a new file in a text editor, type the commands, and save them in a file with a valid filename with the .ps1 file extension.

The following example is a simple script that gets the services that are running on the current system and saves them to a log file. The log filename is created from the current date.

$date = (get-date).dayofyear
get-service | out-file "$date.log"

To create this script, open a text editor or a script editor, type these commands, and then save them in a file named ServiceLog.ps1.

Parameters in scripts

To define parameters in a script, use a Param statement. The Param statement must be the first statement in a script, except for comments and any #Require statements.

Script parameters work like function parameters. The parameter values are available to all of the commands in the script. All of the features of function parameters, including the Parameter attribute and its named arguments, are also valid in scripts.

When running the script, script users type the parameters after the script name.

The following example shows a Test-Remote.ps1 script that has a ComputerName parameter. Both of the script functions can access the ComputerName parameter value.

param ($ComputerName = $(throw "ComputerName parameter is required."))

function CanPing {
   $error.clear()
   $tmp = test-connection $computername -erroraction SilentlyContinue

   if (!$?)
       {write-host "Ping failed: $ComputerName."; return $false}
   else
       {write-host "Ping succeeded: $ComputerName"; return $true}
}

function CanRemote {
    $s = new-pssession $computername -erroraction SilentlyContinue

    if ($s -is [System.Management.Automation.Runspaces.PSSession])
        {write-host "Remote test succeeded: $ComputerName."}
    else
        {write-host "Remote test failed: $ComputerName."}
}

if (CanPing $computername) {CanRemote $computername}

To run this script, type the parameter name after the script name. For example:

C:\PS> .\test-remote.ps1 -computername Server01

Ping succeeded: Server01
Remote test failed: Server01

For more information about the Param statement and the function parameters, see about_Functions and about_Functions_Advanced_Parameters.

Writing help for scripts

You can write a help topic for a script by using either of the two following methods:

• Comment-Based Help for Scripts

  Create a Help topic by using special keywords in the comments. To create comment-based Help for a script, the comments must be placed at the beginning or end of the script file. For more information about comment-based Help, see about_Comment_Based_Help.

• XML-Based Help for Scripts

  Create an XML-based Help topic, such as the type that is typically created for cmdlets. XML-based Help is required if you are translating Help topics into multiple languages.

To associate the script with the XML-based Help topic, use the .ExternalHelp Help comment keyword. For more information about the ExternalHelp keyword, see about_Comment_Based_Help. For more information about XML-based help, see How to Write Cmdlet Help.

Returning an exit value

By default, scripts do not return an exit status when the script ends. You must use the exit statement to return an exit code from a script. By default, the exit statement returns 0. You can provide a numeric value to return a different exit status. A nonzero exit code typically signals a failure.

On Windows, any number between [int]::MinValue and [int]::MaxValue is allowed.

On Unix, only positive numbers between [byte]::MinValue (0) and [byte]::MaxValue (255) are allowed. A negative number in the range of -1 through -255 is automatically translated into a positive number by adding 256. For example, -2 is transformed to 254.

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.

Script scope and dot sourcing

Each script runs in its own scope. The functions, variables, aliases, and drives that are created in the script exist only in the script scope. You cannot access these items or their values in the scope in which the script runs.

To run a script in a different scope, you can specify a scope, such as Global or Local, or you can dot source the script.

The dot sourcing feature lets you run a script in the current scope instead of in the script scope. When you run a script that is dot sourced, the commands in the script run as though you had typed them at the command prompt. The functions, variables, aliases, and drives that the script creates are created in the scope in which you are working. After the script runs, you can use the created items and access their values in your session.

To dot source a script, type a dot (.) and a space before the script path.

For example:

. C:\scripts\UtilityFunctions.ps1

or

. .\UtilityFunctions.ps1

After the UtilityFunctions.ps1 script runs, the functions and variables that the script creates are added to the current scope.

For example, the UtilityFunctions.ps1 script creates the New-Profile function and the $ProfileName variable.

#In UtilityFunctions.ps1

function New-Profile
{
  Write-Host "Running New-Profile function"
  $profileName = split-path $profile -leaf

  if (test-path $profile)
    {write-error "Profile $profileName already exists on this computer."}
  else
    {new-item -type file -path $profile -force }
}

If you run the UtilityFunctions.ps1 script in its own script scope, the New-Profile function and the $ProfileName variable exist only while the script is running. When the script exits, the function and variable are removed, as shown in the following example.

C:\PS> .\UtilityFunctions.ps1

C:\PS> New-Profile
The term 'new-profile' is not recognized as a cmdlet, function, operable
program, or script file. Verify the term and try again.
At line:1 char:12
+ new-profile <<<<
   + CategoryInfo          : ObjectNotFound: (new-profile:String) [],
   + FullyQualifiedErrorId : CommandNotFoundException

C:\PS> $profileName
C:\PS>

When you dot source the script and run it, the script creates the New-Profile function and the $ProfileName variable in your session in your scope. After the script runs, you can use the New-Profile function in your session, as shown in the following example.

C:\PS> . .\UtilityFunctions.ps1

C:\PS> New-Profile

    Directory: C:\Users\juneb\Documents\WindowsPowerShell

    Mode    LastWriteTime     Length Name
    ----    -------------     ------ ----
    -a---   1/14/2009 3:08 PM      0 Microsoft.PowerShellISE_profile.ps1

C:\PS> $profileName
Microsoft.PowerShellISE_profile.ps1

For more information about scope, see about_Scopes.

Scripts in modules

A module is a set of related PowerShell resources that can be distributed as a unit. You can use modules to organize your scripts, functions, and other resources. You can also use modules to distribute your code to others, and to get code from trusted sources.

You can include scripts in your modules, or you can create a script module, which is a module that consists entirely or primarily of a script and supporting resources. A script module is just a script with a .psm1 file extension.

For more information about modules, see about_Modules.

Other script features

PowerShell has many useful features that you can use in scripts.

• #Requires - You can use a #Requires statement to prevent a script from running without specified modules or snap-ins and a specified version of PowerShell. For more information, see about_Requires.

• $PSCommandPath - Contains the full path and name of the script that is being run. This parameter is valid in all scripts. This automatic variable is introduced in PowerShell 3.0.

• $PSScriptRoot - Contains the directory from which a script is being run. In PowerShell 2.0, this variable is valid only in script modules (.psm1). Beginning in PowerShell 3.0, it is valid in all scripts.

• $MyInvocation - The $MyInvocation automatic variable contains information about the current script, including information about how it was started or "invoked." You can use this variable and its properties to get information about the script while it is running. For example, the $MyInvocation.MyCommand.Path variable contains the path and filename of the script. $MyInvocation.Line contains the command that started the script, including all parameters and values.

  Beginning in PowerShell 3.0, $MyInvocation has two new properties that provide information about the script that called or invoked the current script. The values of these properties are populated only when the invoker or caller is a script.

  • PSCommandPath contains the full path and name of the script that called or invoked the current script.

  • PSScriptRoot contains the directory of the script that called or invoked the current script.

  Unlike the $PSCommandPath and $PSScriptRoot automatic variables, which contain information about the current script, the PSCommandPath and PSScriptRoot properties of the $MyInvocation variable contain information about the script that called the current script.

• Data sections - You can use the Data keyword to separate data from logic in scripts. Data sections can also make localization easier. For more information, see about_Data_Sections and about_Script_Internationalization.

• Script Signing - You can add a digital signature to a script. Depending on the execution policy, you can use digital signatures to restrict the running of scripts that could include unsafe commands. For more information, see about_Execution_Policies and about_Signing.

See also

• about_Command_Precedence
• about_Comment_Based_Help
• about_Execution_Policies
• about_Functions
• about_Modules
• about_Profiles
• about_Requires
• about_Run_With_PowerShell
• about_Scopes
• about_Script_Blocks
• about_Signing
• Invoke-Command