I have a script with parameters. In order to ease the debug of the script I create a small function I found on the net to list all my variables. In order to do so, I start by getting all existing variables at the top of the script, then I create a function which compares recorded variables before and after getting parameters
Problem is when I put the $AutomaticVariables and the function before param declaration, PowerShell gives me the following error for any parameter where I set a default value. Is there anyway to workaround this … bug? If it's not a bug, why the hell this behavior. I don't see the point.
The assignment expression is not valid. The input to an assignment operator must be an object that is able to accept assignments, such as a
variable or a property.
# Array and function to debug script variable content
$AutomaticVariables = Get-Variable
function check_variables {
Compare-Object (Get-Variable) $AutomaticVariables -Property Name -PassThru |
Where -Property Name -ne "AutomaticVariables"
}
param(
[String]$hostname,
[String]$jobdesc,
[String]$type = "standard",
[String]$repo,
[String]$ocred,
[String]$site,
[String]$cred = "SRC-$($site)-adm",
[String]$sitetype,
[String]$room,
[String]$chsite = "chub"
)
# TEST - Display variables
check_variables
As mentioned in the comments, you should gather the variables you want to exclude in the calling scope:
Define function (could as well be a script), notice the $DebugFunc parameter I've added at the end:
function Do-Stuff
{
param(
[String]$hostname,
[String]$jobdesc,
[String]$type = "standard",
[String]$repo,
[String]$ocred,
[String]$site,
[String]$cred = "SRC-$($site)-adm",
[String]$sitetype,
[String]$room,
[String]$chsite = "chub",
[scriptblock]$DebugFunc
)
if($PSBoundParameters.ContainsKey('DebugFunc')){
. $DebugFunc
}
}
Now, gather the variables and define your function, then inject it into Do-Stuff:
# Array and function to debug script variable content
$AutomaticVariables = Get-Variable
function check_variables {
Compare-Object (Get-Variable) $AutomaticVariables -Property Name -PassThru | Where -Property Name -ne "AutomaticVariables"
}
Do-Stuff -DebugFunc $Function:check_variables
It's not a bug. The param section defines the input parameter of your script thus has to be the first statement (same as with functions). There is no need to perform any action before the param block.
If you explain what you want to achieve with your check_variables (not what it does). We probably can show you how to do it right.
Related
I am trying to have a function that can count jobs based on the LatestStatus value that I would pass a parameter. So far what I got:
Function JobCountStatus {
Write-Output (Get-VBRJob | ?{$_.Info.LatestStatus -eq $args} | Measure-Object).Count
}
The issue is that as I've read somewhere there will be a subshell(?) executing the where so the argument is not passed.
If I replace the $args with a specific string like "Failed" it will work.
Is there a way to overcome this? I do not want to write separate functions for all possible values.
I would appreciate any comments - Thanks
Well you can just name the value when you run the function as $args is an Automatic Variable
JobCountStatus "Failed"
You can use an advanced function with a parameter, named or not:
function JobCountStatus {
[CmdletBinding()]
Param (
[Parameter(Mandatory = $true, Position = 0)]
[System.String]
$Status
)
Process {
(Get-VBRJob | Where-Object { $_.Info.LatestStatus -eq $Status } | Measure-Object).Count
}
}
And call it like so:
JobCountStatus -Status "Failed"
# OR
JobCountStatus "Failed"
The latter having the same end result as just using $args. The only possible advantage to specifying your own parameter here is you could define a ValidateSet of statuses or an Enum of Status values so you can tab through them. An example of the former would be like so:
function JobCountStatus {
[CmdletBinding()]
Param (
[Parameter(Mandatory = $true, Position = 0)]
[ValidateSet("Failed", "Running", "Successful", "Unknown")]
[System.String]
$Status
)
Process {
(Get-VBRJob | Where-Object { $_.Info.LatestStatus -eq $Status } | Measure-Object).Count
}
}
$args is an array, not a single value. In any case, a ScriptBlock {} is an unnamed function and $args has it's own meaning within it, so you can't use it without some modification in something like Where-Object. You would have to store the elements of $args as another variable or multiple variables to reference within a child ScriptBlock. Not a huge change for this function, but for one where more parameters are expected this can result in a lot of unnecessary code which can be difficult to maintain.
I prefer to recommend defining named parameters in most cases, and this would be a simpler change than making the parent $args work in a child ScriptBlock:
Function JobCountStatus {
Param(
[string]$Status
)
( Get-VBRJob | Where-Object { $_.Info.LatestStatus -eq $Status } ).Count
}
I've also made a few more changes in this function, I'll explain below:
Use Param() to strongly define parameters by name. You could use the simpler syntax of function JobCountStatus([string]$Status) {} but for this case it's really a matter of preference for which technique to use. Using Param() is something I recommend as a matter of convention, but you'll need to use either technique to get a named parameter.
I replaced the $args reference with $Status.
Your use of Measure-Object is extraneous and so I've removed it. Where-Object returns a collection which already has the Count property.
You can use ? if you want but it's considered best practice to omit aliases and use full cmdlet names in scripts and modules, so I've replaced ? with Where-Object.
Note that you can invoke the function/cmdlet (the difference is minimal for PowerShell-defined cmdlets) with or without the parameter, as when you don't define a positional order, the order is automatically determined in the order of declaration:
# Either will work
JobCountStatus -Status Running
JobCountStatus Running
Here is some more documentation you may find useful:
About Functions
About Advanced Functions
#Ash's answer gives some more advanced examples of what you can do with param() which are mentioned in the the Advanced Functions link above. You cannot use advanced parameter attributes with the simple function syntax I mentioned in the first bullet point.
I created a function to import HR records so they're easily accessible by indexing the employeeID.
function hrDataImport {
$HRFile=Import-Csv $rawHRFile #$rawHRFile path previously defined
Write-Host "Creating HR hash table..."
$hrData = #{}
$HRFile | ForEach-Object { $hrData[$_.employeeID] = $_ }
Write-Host "Done. " $hrData.Count
}
I'd like to use that $hrData variable outside the function. I can't reference $hrData['employeeID'] as I've read that variables in functions don't exist outside the function. One thing I tried is creating another function to pass an employeeID into the $hrData hashtable:
function showHRData {
param ([string]$hrUser)
$hrData[$hrUser]
}
I put the functions in a module and imported successfully. I'm able to execute importHRData fine but when I try showHRData -hrUser $employeeID I get "Cannot index into a null array". Seems like the function does not see the hashtable variable from the previous function. What am I doing wrong or what would you suggest so I can access that $hrData hashtable across various scripts?
You might create a Hashtable within your function using a $global (or $script) scope like this:
function hrDataImport {
$HRFile = Import-Csv $rawHRFile #$rawHRFile path previously defined
Write-Host "Creating HR hash table..."
if (!$hrData) { $Global:hrData = #{} }
$HRFile | ForEach-Object { $Global:hrData[$_.employeeID] = $_ }
Write-Host "Done. " $hrData.Count
}
But in general it is advised to avoid the global (or script) scope mainly because it might conflict with variables in the current scope.
To minimize this possibility, I would consider to change the responsibility of your function to not only loading the information but also to receiving the concerned employeeID, e.g.:
function Get-EmployeeData ($EmployeeID) {
if (!$StaticEmployeeData) {
Write-Host "Creating HR hash table..."
$HRFile = Import-Csv $rawHRFile #$rawHRFile path previously defined
$Global:StaticEmployeeData = #{}
$HRFile | ForEach-Object { $Global:StaticEmployeeData[$_.employeeID] = $_ }
Write-Host "Done. " $StaticEmployeeData.Count
}
$Global:StaticEmployeeData[$employeeID]
}
function showHRData {
param ([string]$hrUser)
Get-EmployeeData $hrUser
}
In that case you might choose for a more specific global variable name (e.g. $StaticEmployeeData, knowing that PowerShell doesn't support something like a static variable) and as an extra bonus the data is only loaded the first time you really need it (lazy evaluation).
How can I pass strings by reference to the parent scope?
This doesn't work since strings are not acceptable "values".
function Submit([ref]$firstName){
$firstName.value = $txtFirstName.Text
}
$firstName = $null
Submit([ref]$firstName)
$firstName
Error: "Property 'value' cannot be found on this object; make sure it exists and is settable"
Doing this doesn't give an error but it doesn't change the variable either:
$firstName = "nothing"
function Submit([ref]$firstName){
$firstName = $txtFirstName.Text
}
Submit([ref]$firstName)
$firstName
Edit:
Doing the first code block by itself works. However when trying to do it in my script it returns the error again. I fixed it enough for it to assign the variable and do what I want but it still throws up an error and I was wondering how to fix that. I think it's because it doesn't like variable;es changing during a running session. Here is a link to my script
https://github.com/InconspicuousIntern/Form/blob/master/Form.ps1
Your first snippet is conceptually correct and works as intended - by itself it does not produce the "Property 'Value' cannot be found on this object" error.
You're seeing the error only as part of the full script you link to, because of the following line:
$btnSubmit.Add_Click({ Submit })
This line causes your Submit function to be called without arguments, which in turn causes the $firstName parameter value to be $null, which in turn causes the error quoted above when you assign to $firstName.Value.
By contrast, the following invocation of Submit, as in your first snippet, is correct:
Submit ([ref] $firstName) # Note the recommended space after 'Submit' - see below.
[ref] $firstName creates a (transient) reference to the caller's $firstName variable, which inside Submit binds to (local) parameter variable $firstName (the two may, but needn't and perhaps better not have the same name), where $firstName.Value can then be used to modify the caller's $firstName variable.
Syntax note: I've intentionally placed a space between Submit and ([ref] $firstName) to make one thing clearer:
The (...) (parentheses) here do not enclose the entire argument list, as they would in a method call, they enclose the single argument [ref] $firstName - of necessity, because that expression wouldn't be recognized as such otherwise.
Function calls in PowerShell are parsed in so-called argument mode, whose syntax is more like that of invoking console applications: arguments are space-separated, and generally only need quoting if they contain special characters.
For instance, if you also wanted to pass string 'foo', as the 2nd positional parameter, to Submit:
Submit ([ref] $firstName) foo
Note how the two arguments are space-separated and how foo needn't be quoted.
As for an alternative approach:
[ref]'s primary purpose is to enable .NET method calls that have ref / out parameters, and, as shown above, using [ref] is nontrivial.
For calls to PowerShell functions there are generally simpler solutions.
For instance, you can pass a custom object to your function and let the function update its properties with the values you want to return, which naturally allows multiple values to be "returned"; e.g.:
function Submit($outObj){
$outObj.firstName = 'a first name'
}
# Initialize the custom object that will receive values inside
# the Submit function.
$obj = [pscustomobject] #{ firstName = $null }
# Pass the custom object to Submit.
# Since a custom object is a reference type, a *reference* to it
# is bound to the $outObj parameter variable.
Submit $obj
$obj.firstName # -> 'a first name'
Alternatively, you can just let Submit construct the custom object itself, and simply output it:
function Submit {
# Construct and (implicitly) output a custom
# object with all values of interest.
[pscustomobject] #{
firstName = 'a first name'
}
}
$obj = Submit
$obj.firstName # -> 'a first name'
Please try this out and see if you are getting the same results? It is working for me, and I really did not change much.
$txtFirstName = [PSCustomObject]#{
Text = "Something"
}
function Submit([ref]$var){
$var.value = $txtFirstName.Text
}
$firstName = $null
Submit([ref]$firstName)
$firstName
Can someone tell me, why this function call does not work and why the argument is always empty ?
function check([string]$input){
Write-Host $input #empty line
$count = $input.Length #always 0
$test = ([ADSI]::Exists('WinNT://./'+$input)) #exception (empty string)
return $test
}
check 'test'
Trying to get the info if an user or usergroup exists..
Best regards
$input is an automatic variable.
https://technet.microsoft.com/ru-ru/library/hh847768.aspx
$Input
Contains an enumerator that enumerates all input that is passed to a function. The $input variable is available only to functions and script blocks (which are unnamed functions). In the Process block of a function, the $input variable enumerates the object that is currently in the pipeline. When the Process block completes, there are no objects left in the pipeline, so the $input variable enumerates an empty collection. If the function does not have a Process block, then in the End block, the $input variable enumerates the collection of all input to the function.
Perhaps use a param block for parameters.
https://technet.microsoft.com/en-us/magazine/jj554301.aspx
Update: the problem seems to be fixed if you don't use $input as a parameter name, maybe not a bad thing to have proper variable names ;)
Also Powershell doesn't have return keyword, you just push the object as a statement by itself, this will be returned by function:
function Get-ADObjectExists
{
param(
[Parameter(Mandatory=$true, ValueFromPipeline=$true)]
[string]
$ObjectName
)
#return result by just calling the object (no return statement in powershell)
([ADSI]::Exists('WinNT://./'+$ObjectName))
}
Get-ADObjectExists -ObjectName'test'
Here is my code:
function Get-OSInfo {
param([string]$Computer)
$OS = gwmi -class Win32_OperatingSystem -computer $Computer
$OS | Add-Member –MemberType NoteProperty –Name OSType –Value ""
$OS.OSType = Get-OSType -Input $OS
write $OS
}
function Get-OSType {
param([?]$Input)
if ($Input.ProductType -eq 1) {
write "Client OS"
}
}
$blah = Get-OSInfo -Computer mypc
$blah | fl *
I realize that this could be done with a single function (or in the body of the script itself), but I have simplified the functions to highlight the trouble I'm having. What I want to do is pass the gwmi dataset from the Get-OSInfo function as a parameter variable in the Get-OSType so I can reference all of its properties in the second function without passing them individually from the first. Clear as mud?
I have tried multiple parameter accelerator types, [ref], [array], [object[]], etc., but I haven't found anything that works as a parameter. The only thing that has proven to work is to change the second function to use args[0] for accepting input, but that is not as clean as using parameters, and since it works, I can't help but think there is a parameter that should work as well.
Avoid using $input as that has special meaning in functions (representing pipeline input). Just rename the parameter to something like $OS.
The docs (man about_automatic_variables) on $input say:
Contains an enumerator that enumerates all input that is
passed to a function. The $input variable is available only to
functions and script blocks (which are unnamed functions). In the
Process block of a function, the $input variable enumerates the
object that is currently in the pipeline. When the Process block
completes, there are no objects left in the pipeline, so the $input
variable enumerates an empty collection. If the function does not
have a Process block, then in the End block, the $input variable
enumerates the collection of all input to the function.