I'm writing a script to backup existing bit locker keys to the associated device in Azure AD, I've created a function which goes through the bit locker enabled volumes and backs up the key to Azure however would like to know how I can check that the function has completed successfully without any errors. Here is my code. I've added a try and catch into the function to catch any errors in the function itself however how can I check that the Function has completed succesfully - currently I have an IF statement checking that the last command has run "$? - is this correct or how can I verify please?
function Invoke-BackupBDEKeys {
##Get all current Bit Locker volumes - this will ensure keys are backed up for devices which may have additional data drives
$BitLockerVolumes = Get-BitLockerVolume | select-object MountPoint
foreach ($BDEMountPoint in $BitLockerVolumes.mountpoint) {
try {
#Get key protectors for each of the BDE mount points on the device
$BDEKeyProtector = Get-BitLockerVolume -MountPoint $BDEMountPoint | select-object -ExpandProperty keyprotector
#Get the Recovery Password protector - this will be what is backed up to AAD and used to recover access to the drive if needed
$KeyId = $BDEKeyProtector | Where-Object {$_.KeyProtectorType -eq 'RecoveryPassword'}
#Backup the recovery password to the device in AAD
BackupToAAD-BitLockerKeyProtector -MountPoint $BDEMountPoint -KeyProtectorId $KeyId.KeyProtectorId
}
catch {
Write-Host "An error has occured" $Error[0]
}
}
}
#Run function
Invoke-BackupBDEKeys
if ($? -eq $true) {
$ErrorActionPreference = "Continue"
#No errors ocurred running the last command - reg key can be set as keys have been backed up succesfully
$RegKeyPath = 'custom path'
$Name = 'custom name'
New-ItemProperty -Path $RegKeyPath -Name $Name -Value 1 -Force
Exit
}
else {
Write-Host "The backup of BDE keys were not succesful"
#Exit
}
Unfortunately, as of PowerShell 7.2.1, the automatic $? variable has no meaningful value after calling a written-in-PowerShell function (as opposed to a binary cmdlet) . (More immediately, even inside the function, $? only reflects $false at the very start of the catch block, as Mathias notes).
If PowerShell functions had feature parity with binary cmdlets, then emitting at least one (non-script-terminating) error, such as with Write-Error, would set $? in the caller's scope to $false, but that is currently not the case.
You can work around this limitation by using $PSCmdlet.WriteError() from an advanced function or script, but that is quite cumbersome. The same applies to $PSCmdlet.ThrowTerminatingError(), which is the only way to create a statement-terminating error from PowerShell code. (By contrast, the throw statement generates a script-terminating error, i.e. terminates the entire script and its callers - unless a try / catch or trap statement catches the error somewhere up the call stack).
See this answer for more information and links to relevant GitHub issues.
As a workaround, I suggest:
Make your function an advanced one, so as to enable support for the common -ErrorVariable parameter - it allows you to collect all non-terminating errors emitted by the function in a self-chosen variable.
Note: The self-chosen variable name must be passed without the $; e.g., to collection in variable $errs, use -ErrorVariable errs; do NOT use Error / $Error, because $Error is the automatic variable that collects all errors that occur in the entire session.
You can combine this with the common -ErrorAction parameter to initially silence the errors (-ErrorAction SilentlyContinue), so you can emit them later on demand. Do NOT use -ErrorAction Stop, because it will render -ErrorVariable useless and instead abort your script as a whole.
You can let the errors simply occur - no need for a try / catch statement: since there is no throw statement in your code, your loop will continue to run even if errors occur in a given iteration.
Note: While it is possible to trap terminating errors inside the loop with try / catch and then relay them as non-terminating ones with $_ | Write-Error in the catch block, you'll end up with each such error twice in the variable passed to -ErrorVariable. (If you didn't relay, the errors would still be collected, but not print.)
After invocation, check if any errors were collected, to determine whether at least one key wasn't backed up successfully.
As an aside: Of course, you could alternatively make your function output (return) a Boolean ($true or $false) to indicate whether errors occurred, but that wouldn't be an option for functions designed to output data.
Here's the outline of this approach:
function Invoke-BackupBDEKeys {
# Make the function an *advanced* function, to enable
# support for -ErrorVariable (and -ErrorAction)
[CmdletBinding()]
param()
# ...
foreach ($BDEMountPoint in $BitLockerVolumes.mountpoint) {
# ... Statements that may cause errors.
# If you need to short-circuit a loop iteration immediately
# after an error occurred, check each statement's return value; e.g.:
# if (-not $BDEKeyProtector) { continue }
}
}
# Call the function and collect any
# non-terminating errors in variable $errs.
# IMPORTANT: Pass the variable name *without the $*.
Invoke-BackupBDEKeys -ErrorAction SilentlyContinue -ErrorVariable errs
# If $errs is an empty collection, no errors occurred.
if (-not $errs) {
"No errors occurred"
# ...
}
else {
"At least one error occurred during the backup of BDE keys:`n$errs"
# ...
}
Here's a minimal example, which uses a script block in lieu of a function:
& {
[CmdletBinding()] param() Get-Item NoSuchFile
} -ErrorVariable errs -ErrorAction SilentlyContinue
"Errors collected:`n$errs"
Output:
Errors collected:
Cannot find path 'C:\Users\jdoe\NoSuchFile' because it does not exist.
As stated elsewhere, the try/catch you're using is what is preventing the relay of the error condition. That is by design and the very intentional reason for using try/catch.
What I would do in your case is either create a variable or a file to capture the error info. My apologies to anyone named 'Bob'. It's the variable name that I always use for quick stuff.
Here is a basic sample that works:
$bob = (1,2,"blue",4,"notit",7)
$bobout = #{} #create a hashtable for errors
foreach ($tempbob in $bob) {
$tempbob
try {
$tempbob - 2 #this will fail for a string
} catch {
$bobout.Add($tempbob,"not a number") #store a key/value pair (current,msg)
}
}
$bobout #output the errors
Here we created an array just to use a foreach. Think of it like your $BDEMountPoint variable.
Go through each one, do what you want. In the }catch{}, you just want to say "not a number" when it fails. Here's the output of that:
-1
0
2
5
Name Value
---- -----
notit not a number
blue not a number
All the numbers worked (you can obvious surpress output, this is just for demo).
More importantly, we stored custom text on failure.
Now, you might want a more informative error. You can grab the actual error that happened like this:
$bob = (1,2,"blue",4,"notit",7)
$bobout = #{} #create a hashtable for errors
foreach ($tempbob in $bob) {
$tempbob
try {
$tempbob - 2 #this will fail for a string
} catch {
$bobout.Add($tempbob,$PSItem) #store a key/value pair (current,error)
}
}
$bobout
Here we used the current variable under inspection $PSItem, also commonly referenced as $_.
-1
0
2
5
Name Value
---- -----
notit Cannot convert value "notit" to type "System.Int32". Error: "Input string was not in ...
blue Cannot convert value "blue" to type "System.Int32". Error: "Input string was not in a...
You can also parse the actual error and take action based on it or store custom messages. But that's outside the scope of this answer. :)
If I have a function which accepts more than one string parameter, the first parameter seems to get all the data assigned to it, and remaining parameters are passed in as empty.
A quick test script:
Function Test([string]$arg1, [string]$arg2)
{
Write-Host "`$arg1 value: $arg1"
Write-Host "`$arg2 value: $arg2"
}
Test("ABC", "DEF")
The output generated is
$arg1 value: ABC DEF
$arg2 value:
The correct output should be:
$arg1 value: ABC
$arg2 value: DEF
This seems to be consistent between v1 and v2 on multiple machines, so obviously, I'm doing something wrong. Can anyone point out exactly what?
Parameters in calls to functions in PowerShell (all versions) are space-separated, not comma separated. Also, the parentheses are entirely unneccessary and will cause a parse error in PowerShell 2.0 (or later) if Set-StrictMode -Version 2 or higher is active. Parenthesised arguments are used in .NET methods only.
function foo($a, $b, $c) {
"a: $a; b: $b; c: $c"
}
ps> foo 1 2 3
a: 1; b: 2; c: 3
The correct answer has already been provided, but this issue seems prevalent enough to warrant some additional details for those wanting to understand the subtleties.
I would have added this just as a comment, but I wanted to include an illustration--I tore this off my quick reference chart on PowerShell functions. This assumes function f's signature is f($a, $b, $c):
Thus, one can call a function with space-separated positional parameters or order-independent named parameters. The other pitfalls reveal that you need to be cognizant of commas, parentheses, and white space.
For further reading, see my article Down the Rabbit Hole: A Study in PowerShell Pipelines, Functions, and Parameters. The article contains a link to the quick reference/wall chart as well.
There are some good answers here, but I wanted to point out a couple of other things. Function parameters are actually a place where PowerShell shines. For example, you can have either named or positional parameters in advanced functions like so:
function Get-Something
{
Param
(
[Parameter(Mandatory=$true, Position=0)]
[string] $Name,
[Parameter(Mandatory=$true, Position=1)]
[int] $Id
)
}
Then you could either call it by specifying the parameter name, or you could just use positional parameters, since you explicitly defined them. So either of these would work:
Get-Something -Id 34 -Name "Blah"
Get-Something "Blah" 34
The first example works even though Name is provided second, because we explicitly used the parameter name. The second example works based on position though, so Name would need to be first. When possible, I always try to define positions so both options are available.
PowerShell also has the ability to define parameter sets. It uses this in place of method overloading, and again is quite useful:
function Get-Something
{
[CmdletBinding(DefaultParameterSetName='Name')]
Param
(
[Parameter(Mandatory=$true, Position=0, ParameterSetName='Name')]
[string] $Name,
[Parameter(Mandatory=$true, Position=0, ParameterSetName='Id')]
[int] $Id
)
}
Now the function will either take a name, or an id, but not both. You can use them positionally, or by name. Since they are a different type, PowerShell will figure it out. So all of these would work:
Get-Something "some name"
Get-Something 23
Get-Something -Name "some name"
Get-Something -Id 23
You can also assign additional parameters to the various parameter sets. (That was a pretty basic example obviously.) Inside of the function, you can determine which parameter set was used with the $PsCmdlet.ParameterSetName property. For example:
if($PsCmdlet.ParameterSetName -eq "Name")
{
Write-Host "Doing something with name here"
}
Then, on a related side note, there is also parameter validation in PowerShell. This is one of my favorite PowerShell features, and it makes the code inside your functions very clean. There are numerous validations you can use. A couple of examples are:
function Get-Something
{
Param
(
[Parameter(Mandatory=$true, Position=0)]
[ValidatePattern('^Some.*')]
[string] $Name,
[Parameter(Mandatory=$true, Position=1)]
[ValidateRange(10,100)]
[int] $Id
)
}
In the first example, ValidatePattern accepts a regular expression that assures the supplied parameter matches what you're expecting. If it doesn't, an intuitive exception is thrown, telling you exactly what is wrong. So in that example, 'Something' would work fine, but 'Summer' wouldn't pass validation.
ValidateRange ensures that the parameter value is in between the range you expect for an integer. So 10 or 99 would work, but 101 would throw an exception.
Another useful one is ValidateSet, which allows you to explicitly define an array of acceptable values. If something else is entered, an exception will be thrown. There are others as well, but probably the most useful one is ValidateScript. This takes a script block that must evaluate to $true, so the sky is the limit. For example:
function Get-Something
{
Param
(
[Parameter(Mandatory=$true, Position=0)]
[ValidateScript({ Test-Path $_ -PathType 'Leaf' })]
[ValidateScript({ (Get-Item $_ | select -Expand Extension) -eq ".csv" })]
[string] $Path
)
}
In this example, we are assured not only that $Path exists, but that it is a file, (as opposed to a directory) and has a .csv extension. ($_ refers to the parameter, when inside your scriptblock.) You can also pass in much larger, multi-line script blocks if that level is required, or use multiple scriptblocks like I did here. It's extremely useful and makes for nice clean functions and intuitive exceptions.
You call PowerShell functions without the parentheses and without using the comma as a separator. Try using:
test "ABC" "DEF"
In PowerShell the comma (,) is an array operator, e.g.
$a = "one", "two", "three"
It sets $a to an array with three values.
Function Test([string]$arg1, [string]$arg2)
{
Write-Host "`$arg1 value: $arg1"
Write-Host "`$arg2 value: $arg2"
}
Test "ABC" "DEF"
If you're a C# / Java / C++ / Ruby / Python / Pick-A-Language-From-This-Century developer and you want to call your function with commas, because that's what you've always done, then you need something like this:
$myModule = New-Module -ascustomobject {
function test($arg1, $arg2) {
echo "arg1 = $arg1, and arg2 = $arg2"
}
}
Now call:
$myModule.test("ABC", "DEF")
and you'll see
arg1 = ABC, and arg2 = DEF
Because this is a frequent viewed question, I want to mention that a PowerShell function should use approved verbs (Verb-Noun as the function name).
The verb part of the name identifies the action that the cmdlet performs. The noun part of the name identifies the entity on which the action is performed. This rule simplifies the usage of your cmdlets for advanced PowerShell users.
Also, you can specify things like whether the parameter is mandatory and the position of the parameter:
function Test-Script
{
[CmdletBinding()]
Param
(
[Parameter(Mandatory=$true, Position=0)]
[string]$arg1,
[Parameter(Mandatory=$true, Position=1)]
[string]$arg2
)
Write-Host "`$arg1 value: $arg1"
Write-Host "`$arg2 value: $arg2"
}
To pass the parameter to the function you can either use the position:
Test-Script "Hello" "World"
Or you specify the parameter name:
Test-Script -arg1 "Hello" -arg2 "World"
You don't use parentheses like you do when you call a function within C#.
I would recommend to always pass the parameter names when using more than one parameter, since this is more readable.
If you don't know (or care) how many arguments you will be passing to the function, you could also use a very simple approach like;
Code:
function FunctionName()
{
Write-Host $args
}
That would print out all arguments. For example:
FunctionName a b c 1 2 3
Output
a b c 1 2 3
I find this particularly useful when creating functions that use external commands that could have many different (and optional) parameters, but relies on said command to provide feedback on syntax errors, etc.
Here is a another real-world example (creating a function to the tracert command, which I hate having to remember the truncated name);
Code:
Function traceroute
{
Start-Process -FilePath "$env:systemroot\system32\tracert.exe" -ArgumentList $args -NoNewWindow
}
If you try:
PS > Test("ABC", "GHI") ("DEF")
you get:
$arg1 value: ABC GHI
$arg2 value: DEF
So you see that the parentheses separates the parameters
If you try:
PS > $var = "C"
PS > Test ("AB" + $var) "DEF"
you get:
$arg1 value: ABC
$arg2 value: DEF
Now you could find some immediate usefulness of the parentheses - a space will not become a separator for the next parameter - instead you have an eval function.
I don't see it mentioned here, but splatting your arguments is a useful alternative and becomes especially useful if you are building out the arguments to a command dynamically (as opposed to using Invoke-Expression). You can splat with arrays for positional arguments and hashtables for named arguments. Here are some examples:
Note: You can use positional splats with external commands arguments with relative ease, but named splats are less useful with external commands. They work, but the program must accept arguments in the -Key:Value format as each parameter relates to the hashtable key/value pairs. One example of such software is the choco command from the Chocolatey package manager for Windows.
Splat With Arrays (Positional Arguments)
Test-Connection with Positional Arguments
Test-Connection www.google.com localhost
With Array Splatting
$argumentArray = 'www.google.com', 'localhost'
Test-Connection #argumentArray
Note that when splatting, we reference the splatted variable with an # instead of a $. It is the same when using a Hashtable to splat as well.
Splat With Hashtable (Named Arguments)
Test-Connection with Named Arguments
Test-Connection -ComputerName www.google.com -Source localhost
With Hashtable Splatting
$argumentHash = #{
ComputerName = 'www.google.com'
Source = 'localhost'
}
Test-Connection #argumentHash
Splat Positional and Named Arguments Simultaneously
Test-Connection With Both Positional and Named Arguments
Test-Connection www.google.com localhost -Count 1
Splatting Array and Hashtables Together
$argumentHash = #{
Count = 1
}
$argumentArray = 'www.google.com', 'localhost'
Test-Connection #argumentHash #argumentArray
Function Test([string]$arg1, [string]$arg2)
{
Write-Host "`$arg1 value: $arg1"
Write-Host "`$arg2 value: $arg2"
}
Test("ABC") ("DEF")
I don't know what you're doing with the function, but have a look at using the 'param' keyword. It's quite a bit more powerful for passing parameters into a function, and makes it more user friendly. Below is a link to an overly complex article from Microsoft about it. It isn't as complicated as the article makes it sound.
Param Usage
Also, here is an example from a question on this site:
Check it out.
I stated the following earlier:
The common problem is using the singular form $arg, which is incorrect. It should always be plural as $args.
The problem is not that. In fact, $arg can be anything else. The problem was the use of the comma and the parentheses.
I run the following code that worked and the output follows:
Code:
Function Test([string]$var1, [string]$var2)
{
Write-Host "`$var1 value: $var1"
Write-Host "`$var2 value: $var2"
}
Test "ABC" "DEF"
Output:
$var1 value: ABC
$var2 value: DEF
Function Test {
Param([string]$arg1, [string]$arg2)
Write-Host $arg1
Write-Host $arg2
}
This is a proper params declaration.
See about_Functions_Advanced_Parameters.
And it indeed works.
You can pass parameters in a function like this also:
function FunctionName()
{
Param ([string]$ParamName);
# Operations
}
Say I'm passing a function as a parameter, is there a way to find out the name of the passed function through introspection in powershell? Or do I just have to pass it along with the rest of the parameters?
(without calling the function in question)
The linked question tries to pass a function by name, as a string, in which case the answer is obvious: the argument itself is the function name.
In case a script block is passed instead, you can use the following technique:
function get-ScriptBlockCommandName {
param(
[scriptblock] $ScriptBlock,
[switch] $Expand
)
# Using the script block's AST, extract the first command name / path token.
$commandName = $ScriptBlock.Ast.EndBlock.
Statements[0].PipelineElements.CommandElements[0].Extent.Text
# Expand (interpolate) the raw name, if requested.
if ($Expand) {
$commandName = $ExecutionContext.InvokeCommand.ExpandString($commandName)
}
# Remove outer quoting, if present.
if ($commandName -match '^([''"])(.+)\1$') {
$commandName = $Matches[2]
if ($Matches[1] -eq "'") { $commandName = $commandName -replace "''", "'" }
}
# Output
$commandName
}
The function returns the (first) command name / path that is called from inside the script block.
Caveats:
An error will occur if you pass an expression (e.g., 1 + 2) as the first statement inside the script block.
Only the first command is analyzed (and its command name / path returned), whereas there is no limit to how many statements you can place inside a script block.
By default, if the command name / path is constructed from variables / other commands, these are not expanded (interpolated), given that doing so can result in execution of commands; to opt into expansion, use the -Expand switch.
Example calls:
PS> get-ScriptBlockCommandName { foo -bar baz -more stuff }
foo
This also works with quoted names / paths (note how & must then be used to invoke the command):
PS> get-ScriptBlockCommandName { & '/dir name/foo' -bar baz -more stuff }
/dir name/foo
However, to avoid potentially unwanted execution of commands, the command name / path is returned as-is, with variable references and subexpressions unexpanded.
You can opt to have these expanded by passing -Expand:
PS> get-ScriptBlockCommandName { & "$HOME/scripts/foo.ps1" -bar baz } -Expand
C:/Users/jdoe/scripts.ps1 # e.g.
A PowerShell ScriptBlock is not a lexical closure as it does not close over the variables referenced in its declaring environment. Instead it seems to leverage dynamic scope and free variables which are bound at run time in a lambda expression.
function Get-Block {
$b = "PowerShell"
$value = {"Hello $b"}
return $value
}
$block = Get-Block
& $block
# Hello
# PowerShell is not written as it is not defined in the scope
# in which the block was executed.
function foo {
$value = 5
function bar {
return $value
}
return bar
}
foo
# 5
# 5 is written $value existed during the evaluation of the bar function
# it is my understanding that a function is a named scriptblock
# which is also registered to function:
Calling GetNewClosure() on a ScriptBlock returns a new ScriptBlock which closes over the variables referenced. But this is very limited in scope and ability.
What is a ScriptBlock's classification?
Per the docs, a scriptblock is a "precompiled block of script text." So by default you just a pre-parsed block of script, no more, no less. Executing it creates a child scope, but beyond that it's as if you pasted the code inline. So the most appropriate term would simply be "readonly source code."
Calling GetNewClosure bolts on a dynamically generated Module which basically carries a snapshot of all the variables in the caller's scope at the time of calling GetNewClosure. It is not a real closure, simply a snapshot copy of variables. The scriptblock itself is still just source code, and variable binding does not occur until it is invoked. You can add/remove/edit variables in the attached Module as you wish.
function GetSB
{
$funcVar = 'initial copy'
{"FuncVar is $funcVar"}.GetNewClosure()
$funcVar = 'updated value' # no effect, snapshot is taken when GetNewClosure is called
}
$sb = GetSB
& $sb # FuncVar is initial copy
$funcVar = 'outside'
& $sb # FuncVar is initial copy
$sb.Module.SessionState.PSVariable.Remove('funcVar')
& $sb # FuncVar is outside
A PowerShell ScriptBlock is equivalent to a first-class, anonymous function. Most of the confusion I've seen is not with ScriptBlocks, but with the function keyword.
PowerShell does support function closures, however the function keyword does not.
Examples
Function:
PS> function Hello {
>> param ([string] $thing)
>>
>> return ("Hello " + $thing)
>> }
PS> Hello "World"
"Hello World"
ScriptBlock:
PS> $HelloSB = {
>> param ([string] $thing)
>>
>> return ("Hello " + $thing)
>> }
PS> & $HelloSB "World"
"Hello World"
PS> $HelloRef = $HelloSB
PS> & $HelloRef "Universe"
"Hello Universe"
Closure:
PS> $Greeter = {
>> param ([string] $Greeting)
>>
>> return ( {
>> param ([string] $thing)
>>
>> return ($Greeting + " " + $thing)
>> }.GetNewClosure() )
>> }
PS> $Ahoy = (& $Greeter "Ahoy")
PS> & $Ahoy "World"
"Ahoy World"
PS> $Hola = (& $Greeter "Hola")
PS> & $Hola "Mundo"
"Hola Mundo"
Although you can get around the limitation of the function keyword with the "Set-Item" cmdlet:
PS> function Greeter = { ... } # ✕ Error
PS> function Greeter { ... }.GetNewClosure() # ✕ Error
PS> Set-Item -Path "Function:Greeter" -Value $Greeter # (defined above) ✓ OK
PS> $Hola = Greeter "Hola"
PS> & $Hola "Mundo"
"Hola Mundo"
The Value parameter of the "Set-Item" cmdlet can be any ScriptBlock, even one returned by another function. (The "Greeter" function, for example, returns a closure, as shown above.)
PS> Set-Item -Path "Function:Aloha" -Value (Greeter "Aloha")
PS> Aloha "World"
"Aloha World"
Two other important points:
PowerShell uses dynamic scoping, not lexical scoping.
A lexical closure is closed on its source-code environment, whereas a dynamic closure is closed based on the active/dynamic environment that exists when GetNewClosure() is called. (Which is more appropriate for a scripting language.)
PowerShell may have "functions" and "return" statements, but actually its input/output is based on streams and piping. Anything written out of a ScriptBlock with the "Write-Output" or "write" cmdlet will be returned.
I have a PowerShell module with a group of functions.
The function createService creates an instance of a service and returns a variable. Several of my functions use the returned value, but I only want one instance of the service so I cannot call createService in each function.
On the command line, I can do $var = createService($string), then call update($var) and it will work properly, but I don't want to force the user to remember to use $var as a parameter.
Is there a way to put these functions in an object/class so the variable can be stored globally and referenced inside each function instead of through parameters?
I would propose to start the service by the exposed functions, so that a user does even have to care of starting it.
$module = {
# The only service instance, $null so far
$script:service = $null
# Starts the service once and keeps its the only instance
function Start-MyService {
if ($null -eq $script:service) {
"Starting service"
$script:service = 'MyService'
}
}
# Ensures the service by Start-MyService and then operates on $script:service
function Update-MyService1 {
Start-MyService
"Updating service 1: $script:service"
}
# Ensures the service by Start-MyService and then operates on $script:service
function Update-MyService2 {
Start-MyService
"Updating service 2: $script:service"
}
Export-ModuleMember -Function Update-MyService1, Update-MyService2
}
$null = New-Module $module
# Starting service
# Updating service 1: MyService
Update-MyService1
# Updating service 2: MyService
Update-MyService2
In your module, if you assign the service object to a script scoped variable, all functions in the module can access the variable. Here is an example:
$module = {
function StartNewService {
$script:service = 'MyService'
}
function UpdateService {
"Updating service: " + $script:service
}
Export-ModuleMember -Function StartNewService, UpdateService
}
$null = New-Module $module
# StartNewService creates the service variable.
StartNewService
# UpdateService accesses the service variable created by StartNewService.
UpdateService
If you declare the variable as $global:service, you can access the variable from outside the module as well.
Edit: To address the comments below, here is a more practical example that shows an appropriate situation for sharing a variable among functions in a module. In this case all of the functions in the module depend on the same instance of the $Locations variable. In this example the variable is created outside of the functions, and is kept private by not including it in the Export-ModuleMember command.
Here is a simplified version of my LocationName.psm1
$Locations = #{}
function Save-LocationName {
param(
[parameter(Mandatory=$true)]
[string]$Name
)
$Locations[$Name] = $PWD
}
function Move-LocationName {
param(
[parameter(Mandatory=$true)]
[string]$Name
)
if($Locations[$Name]) {
Set-Location $Locations[$Name]
}
else {
throw ("Location $Name does not exist.")
}
}
New-Alias -Name svln -Value Save-LocationName
New-Alias -Name mvln -Value Move-LocationName
Export-ModuleMember -Function Save-LocationName, Move-LocationName -Alias svln, mvln
With this module a user can give a name to a directory, and move to that location by using the given name. For example if I am at \\server01\c$\Program Files\Publisher\Application\Logs, I can save the location by entering svln logs1. Now if I change my location, I can return to the logs directory with mvln logs1. In this example it would be impractical to use the locations hashtable for input and output since the functions are always working with the same instance.