This PowerShell module allows you to prevent multiple instances of the same PowerShell script from running at the same time.

The SingleInstance module exports the following functions:

• Enter-SingleInstance
• Exit-SingleInstance
• Get-ScriptPath

Use this function to check if any other instances of the script are running by passing the script ID, such as script's path ($PSCommandPath), a GUID, or some other value that only that script would know. If the function detects that no other instances are running, it will create a mutex (named after the script ID), and return true to indicate that this is the first instance. The mutex will be held until the script calls the Exit-SingleInstance function, but before that any other script that calls Enter-SingleInstance will get back false and know that there is another instance of the script running. Keep in mind that if the first instance does not release the mutex (e.g. if the script crashes without cleanup), the mutex will be held until the system is rebooted.

Enter-SingleInstance `
  [-ScriptId <string>] `
  [<CommonParameters>]

-ScriptId

The value uniquely identifying the calling script. If you omit this parameter the module will try to dermine the path to the calling script (.ps1 file) and use this path as the script ID.

-<CommonParameters>

Common PowerShell parameters (cmdlet is not using these explicitly).

Use this function to at the end of the processing to release the single-instance mutex.

Exit-SingleInstance

-<CommonParameters>

Common PowerShell parameters (cmdlet is not using these explicitly).

This is a helper function that you may find useful if you want to determine the path of the calling script from a module. The first script in the call stack identified by the extension will be used to determine the script path.

Get-ScriptPath `
  [-Extension <string>] `
  [<CommonParameters>]

-Extension

Extension by which the calling script will be identified. By default, the '.ps1' extension will be used.

-<CommonParameters>

Common PowerShell parameters (cmdlet is not using these explicitly).

You can download a copy of the module from the Github repository or install it from the PowerShell Gallery (see Examples).

function LoadModule {
    param(
        [string]
        $ModuleName
    )

    if (!(Get-Module -Name $ModuleName)) {

        if (!(Get-Module -Listavailable -Name $ModuleName)) {
            Install-Module -Name $ModuleName -Force -Scope CurrentUser -ErrorAction Stop
        }

        Import-Module $ModuleName -ErrorAction Stop -Force
    }
}

$modules = @("SingleInstance")
foreach ($module in $modules) {
    try {
        LoadModule -ModuleName $module
    }
    catch {
        throw (New-Object System.Exception "Cannot load module $module.", $_.Exception)
    }
}

Downloads the SingleInstance module from the PowerShell Gallery into the PowerShell modules folder for the current user and imports it into the running script.

$modulePath = Join-Path (Split-Path -Path $PSCommandPath -Parent) 'SingleInstance.psm1'
Import-Module $modulePath -ErrorAction Stop -Force

Imports the SingleInstance module from the same directory as the running script.

if (!(Enter-SingleInstance)) {
    throw "The script is already running."
}
else {
    try {
        # Do what you need to do.
    }
    finally {
        # Make sure you exit single instance on both success and failure.
        Exit-SingleInstance
    }
}

Enforces single-instance script execution.