Check function exists in PowerShell module - powershell

Question

I’ve the following PowerShell script which searches in a directory for PowerShell module). All found modules will be imported and stored in a list (using the -PassThru) option.
The scrip iterates over the imported modules and invokes a function defined in the module:
# Discover and import all modules
$modules = New-Object System.Collections.Generic.List[System.Management.Automation.PSModuleInfo]
$moduleFiles = Get-ChildItem -Recurse -Path "$PSScriptRoot\MyModules\" -Filter "Module.psm1"
foreach( $x in $moduleFiles ) {
$modules.Add( (Import-Module -Name $x.FullName -PassThru) )
}
# All configuration values
$config = #{
KeyA = "ValueA"
KeyB = "ValueB"
KeyC = "ValueC"
}
# Invoke 'FunctionDefinedInModule' of each module
foreach( $module in $modules ) {
# TODO: Check function 'FunctionDefinedInModule' exists in module '$module '
& $module FunctionDefinedInModule $config
}
Now I would like to first check if a function is defined in a module before it gets invoked.
How can such a check be implemented?
The reason for adding the check if to avoid the exception thrown when calling a function which doesn’t exists:
& : The term ‘FunctionDefinedInModule’ is not recognized as the name of a cmdlet, function, script file, or operable program

Answer 1

Get-Command can tell you this. You can even use module scope to be sure it comes from a specific module
get-command activedirectory\get-aduser -erroraction silentlycontinue
For example. Evaluate that in an if statement and you should be good to go.

Answer 2

Use Get-Command to check if a function currently exists
if (Get-Command 'FunctionDefinedInModule' -errorAction SilentlyContinue) {
"FunctionDefinedInModule exists"
}

Answer 3

If many functions need to be checked
try{
get-command -Name Get-MyFunction -ErrorAction Stop
get-command -Name Get-MyFunction2 -ErrorAction Stop
}
catch{
Write-host "Load Functions first prior to laod the current script"
}

Answer 4

I needed it so often that I wrote module for this.

Answer 5

Maybe try adding this function to your module?
function DoesFunctionExists {
param(
[string]$Function
)
$FunList = gci function:$Function -ErrorAction 'SilentlyContinue'
foreach ($FunItem in $FunList) {
if ($FunItem.Name -eq $Function) {
return $true
}
}
return $false
}