Not all PowerShell cmdlets ship with PowerShell. Many cmdlets are part of 3rd party modules which in turn ship when you install certain software, or use certain Windows versions.

To find out the compatibility status of your scripts, in our first part we’re looking at ways to find out which commands a script actually uses. Here is a helper function that utilizes the internal PowerShell Abstract Syntax Tree (AST) to identify commands:

function Get-ContainedCommand
{
    param
    (
        [Parameter(Mandatory)][string]
        $Path,

        [string][ValidateSet('FunctionDefinition','Command')]
        $ItemType
    )

    $Token = $Err = $null
    $ast = [Management.Automation.Language.Parser]::ParseFile($Path, [ref] $Token, [ref] $Err)

    $ast.FindAll({ $args[0].GetType().Name -eq "${ItemType}Ast" }, $true) 

Get-ContainedCommand can extract either the functions defined in a script, or the commands used by a script. Here is the code to dump all the functions defined in a script:

$Path = "C:\scriptToPS1File\WithFunctionDefinitionsInIt.ps1"

$functionNames = Get-ContainedCommand $Path -ItemType FunctionDefinition | 
  Select-Object -ExpandProperty Name

$functionNames

This is the list of commands used internally by the script:

$commands = Get-ContainedCommand $Path -ItemType Command 
$commands.Foreach{$_.CommandElements[0].Extent.Text}

To identify the use of external commands, simply subtract all internally defined functions from the command list, and eliminate duplicates. This gets you the list of external commands used by the script:

$Path = "C:\scriptToPS1File\WithFunctionDefinitionsInIt.ps1"

$functionNames = Get-ContainedCommand $Path -ItemType FunctionDefinition | 
  Select-Object -ExpandProperty Name

$commands = Get-ContainedCommand $Path -ItemType Command 

$externalCommands = $commands | Where-Object {
      $commandName = $_.CommandElements[0].Extent.Text
      $commandName -notin $functionNames
  } | 
  Sort-Object -Property { $_.GetCommandName() } -Unique

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