When I have a function, which uses several Write-Output commands and returns single number, how can I get number value in function caller code?
As far as I got, line
[int] $var = Get-MyNumber(...)
gets me the error
Cannot convert the "System.Object[]" value of type "System.Object[]" to type "System.Int32"".
Probably because PowerShell returns an array of objects (containing Write-Output messages) back to caller code, where the assignment to the [int]-typed variable fails. Got that.
Now, how can I tell PowerShell that I'm interested in only a single value from those returned from the function, which is typed as [int].
BTW, I DON'T want to choose output by indexing the return array as I could mess up the indexes in the return array simply by adding another Write-Output line. (Which will happen sooner or later due to code maintenance).
Code
function f1() {
Write-Output "Lala"
return 5
}
[int] $x = f1
Write-Output $x
Results in the same error.
I see from your edit that you are using Write-Output to display a status message.
You should use Write-Host for that, or if you were using an advanced function, I would recommend using Write-Verbose and calling the function with -Verbose when you want to see the messages (see about_CommonParameters).
Updated code:
function f1() {
Write-Host "Lala"
return 5
}
[int] $x = f1
Write-Host $x
Advanced Function Example
function f1 {
[CmdletBinding()]
param()
Write-Verbose "Lala"
return 5
}
$x = f1
# The "Lala" message will not be seen.
$x = f1 -Verbose
# The "Lala" message will be seen.
Why Write-Output seems to work outside of a function:
Write-Output passes the input object to the caller. In the case of code that is executed directly in the host, and not in a function or cmdlet, the caller is the host, and the host decides what to do with it. In the case of powershell.exe (or ISE), it displays it.
Write-Host on the other hand, always writes to the host; it doesn't pass anything back to the caller.
Also note that Write-Output is, basically, optional. The following lines are equivalent:
Write-Output $x
$x
Related
Writing a powershell script with a function that invokes an executable, and then attempts to return a bool. Two errors occur:
The output from the .exe doesn't show in the console window while running
the returned value is contains the output + the return value..
I'm doing something stupid, but what?
Script is
function HelloWorld () {
$cmd = "./HelloWorld.exe"
& $cmd
return $true}
$ret = HelloWorld
The $ret = "Hello World
True"
UPDATED:
Ok, I found a script online to create the helloworld.exe
Add-Type -outputtype consoleapplication -outputassembly helloworld.exe 'public class helloworld{public static void Main(){System.Console.WriteLine("hello world");}}'
Now We can run this:
function HelloWorld {
$cmd = ".\HelloWorld.exe"
& $cmd | Write-Host
return $true
}
$ret = HelloWorld
After run:
hello world
PS> $ret
True
PS> $ret | gm
TypeName: System.Boolean
Seems to work here at least.
HTH
The output is being captured by the assignment to $ret. Important to understand PowerShell functions return all output. when you ran & $cmd the output is returned, then you ran an explicit albeit unnecessary Return $true. Both pieces of data get returned and you see no screen output because it was consumed by the assignment.
In order to get the output of HelloWorld.exe to the console while only returning the Boolean from the function you can use either Write-Host or Out-Host. The difference being the latter traverses PowerShell's for-display formatting system, which may not be necessary in this case.
function HelloWorld ()
{
$cmd = "./HelloWorld.exe"
& $cmd | Write-Host
return $true
}
$return = HelloWorld
In this case the screen should show the output from HellowWorld.exe, but $return should only contain $true.
Note: Because of the aforementioned behavior Return isn't technically necessary. The only necessary use case for Return is to explicitly exit a function usually early.
Also note: this assumes HelloWorld.exe is a typical console application for which PowerShell will capture output into the success stream.
So in the function, there is a call to an executable which had a console.writeline statement (console.writelne("Hello world"))
calling the function works fine, but there no output that appears. Instead it got returned to the caller along with the return true/false. How can I get just the bool return without disrupting the output from the exe which we need to see on the console real time...
I am using VMware PowerCLI to perform some stuff with virtual machines in a PowerShell module with PowerShell 7.1.3. I am seeing some weird behavior with object types. Here's a rundown of what I'm doing:
Parent-Function.ps1:
function Parent-Function {
$osCustomizationSpec = Child-Function -Name "AUTODEPLOY-ExampleConfiguration"
Write-Verbose -Message $osCustomizationSpec.GetType()
}
This prints System.Object[] to the verbose stream
Child-Function.ps1:
function Child-Function {
param([Parameter][string]$Name)
$osCustomizationSpec = Get-OSCustomizationSpec -Name $Name
Write-Verbose -Message $osCustomizationSpec.GetType()
return $osCustomizationSpec
}
This prints VMware.VimAutomation.ViCore.Impl.V1.VIObjectImpl to the verbose stream
Basically, why is the calling function receiving the object as an array of System.Objects, when it's supposed to be returned as a VMware.VimAutomation.ViCore.Impl.V1.VIObjectImpl object?
Because PowerShell returns all output. You’re returning .GetType() then a return. PowerShell will collect that in an an array.
If you return 1 object you’ll get a scalar value of the given type. Return more than 1 object and you’ll get an array.
If those .GetType() calls are for debugging. Front them with Write-Host like:
Write-Host ( $osCustomizationSpec).GetType().FullName
That will write to the console not the output stream.
I would like to invoke an arbitrary expression and redirect std error to a variable without redirection to a file.
For example, in Powershell it is possible to redirect standard error using 2> operator. Using a temporary file, I can easily get what I want:
#$expr = "1/0" # with std error
#$expr = "2+2" # without stderror
#$expr = "Get-Service invalidsvc" # with stderror
$expr = "try { throw '111' } catch { }" # without std error
$ans = Invoke-Expression $expr -ErrorVariable ev 2> C:\log\stderr.txt
if(cat C:\log\stderr){
Write-Host "Error $ev"
}
How can I do the same, but without creation of a temporal output file?
Wrong solutions:
Using -ErrorVariable switch. Counter example:
Invoke-Expression $expr -ErrorVariable ev 2> C:\aaa\file1.txt
$expr = "try { throw '111' } catch { }"
Write-Host "Error $ev" # will output error, but std error is empty
$LASTEXITCODE and $? check. Counter example:
Get-Service invalidservice
$lastexitcode is equal to 0, $? is equal to True, but std error is not empty
The idea is simple: save the "red" (std error) text in Powershell console in a variable. The command I receive is an arbitrary string.
Examples:
When I write "try { throw '111' } catch { }" in Powershell console there will be no red (error) text in PS console (despite the fact $error is not empty). So if I invoke that expression in my code I get no error saved in some variable.
When I write "Get-Service notexistingservice", or "1/0", or "Write-Error 111" there will red (error) text and non-null $error. So if I invoke that expression in my code I would like to get error saved in some variable.
Save standard output and standard error to separate variables. It won't work without the dollar sign (from Windows Powershell in Action).
$err = $( $output = get-childitem foo3 ) 2>&1
The way to do it is the -errorvariable common parameter. Your counter example is only valid (and I only hesitantly use that word) because you have explicitly coded for it to not output an error with the use of the Try/Catch and not including anything coding in your catch. You are basically complaining that you told PowerShell to send error cases to the Catch scriptblock, where you did not output anything, and then having an issue when nothing is output. An error still occurs, it is logged in the errorvariable as you stated it should be, and also stored in $Error, but since you did not output anything in your Catch block there's nothing for your StdErr redirect to do.
If you want $ev to not contain an error because you corrected the issue in your Catch block, then also clear the variable in the catch block.
$expr = 'try{ throw "1111"}catch{Remove-Variable ev}'
Or if you want StdErr to contain the error text, make sure you include that output in your Catch block:
$expr = 'try{ throw "1111"}catch{Write-Error $_.Exception.Message}'
I know this is a very old question but I had the same problem and wanted to share what I ended up with.
$error.clear()
$List = New-Object PSObject
Invoke-Command -ComputerName $server -ScriptBlock {
$smbv1 = (Get-SmbServerConfiguration | Select EnableSMB1Protocol)
$smbv1 | Select-Object EnableSMB1Protocol} -OutVariable List
foreach($item in $list.EnableSMB1Protocol){
if($error -ne $null){
$item = "unknown"
$msg = $error.Exception.Message
ac .\smb1errors.txt "$Server, $msg"
}
Since the $error variable is a .NET object in order to clear it I needed to pass it parameter (). I then executed my code, in this case checking for SMBv1 service, and testing if $error is still $null. If the $error variable has content I grabed it in a variable. $msg = $error.Exception.Message
I wasn't sure how to describe this problem in the title so here goes.
I call a function from a script in another script. In that function i have a while loop that basically keeps looping through a set of ip's and looks up their hostname. when the while loop times out or we have all the host names.
it returns the hostnames.
My problem is that the return value contains every single Write-Host i'm doing in that function.
i know it's because Write-Host puts stuff on the pipeline and the return just returns whatever it has.
How do i go about fixing this?
The entire script i run get's logged in a log file which is why i want to have some verbose logging.
| out-null on write-host fixes the issue but it doesn't print the write-host values in the script.
in main.psm1 i have a function like so:
$nodes = #("ip1", "ip2", "ip3", "ip4")
$nodesnames = DoStuff -nodes $nodes
then in functions.psm1 i have functions like:
Function DoStuff
{
param($nodes)
$timeout = 300
$timetaken = 0
$sleepseconds = 5
$nodenames = #("$env:COMPUTERNAME")
while(($nodenames.count -lt $nodes.count) -and ($timetaken -lt $timeout))
{
try
{
Write-Host "Stuff"
foreach($node in $nodes)
{
$nodename = SuperawesomeFunction $node
Write-Host "$nodename"
if($nodenames -notcontains $nodename)
{
$nodenames += #($nodename)
}
}
}
catch
{
Write-Host "DoStuff Failed because $_"
}
Start-Sleep $sleepseconds
$timetaken += $sleepseconds
}
return $nodenames
}
Function SuperawesomeFunction
{
param($node)
$nodename = [System.Net.Dns]::GetHostEntry("$node")
return $nodename
}
Thanks.
So the answer is, your function is working like it is by design. In PowerShell a function will return output in general to the pipeline, unless specifically directed otherwise.
You used Echo before, which is an alias of Write-Output, and output is passed down the pipe as I mentioned before. As such it would be collected along with the returned $nodenames array.
Replacing Echo with Write-Host changes everything because Write-Host specifically tells PowerShell to send the information to the host application (usually the PowerShell Console or PowerShell ISE).
How do you avoid this? You could add a parameter specifying a path for a logfile, and have your function update the logfile directly, and only output the relevant data.
Or you can make an object with a pair of properties that gets passed back down the pipe which has the DNS results in one property, and the errors in another.
You could use Write-Error in the function, and set it up as an advanced function to support -errorvariable and capture the errors in a separate variable. To be honest, I'm not sure how to do that, I've never done it, but I'm 90% sure that it can be done.
I have developed a PowerShell function that performs a number of actions involving provisioning SharePoint Team sites. Ultimately, I want the function to return the URL of the provisioned site as a String so at the end of my function I have the following code:
$rs = $url.ToString();
return $rs;
The code that calls this function looks like:
$returnURL = MyFunction -param 1 ...
So I am expecting a String, however it's not. Instead, it is an object of type System.Management.Automation.PSMethod. Why is it returning that type instead of a String type?
PowerShell has really wacky return semantics - at least when viewed from a more traditional programming perspective. There are two main ideas to wrap your head around:
All output is captured, and returned
The return keyword really just indicates a logical exit point
Thus, the following two script blocks will do effectively the exact same thing:
$a = "Hello, World"
return $a
$a = "Hello, World"
$a
return
The $a variable in the second example is left as output on the pipeline and, as mentioned, all output is returned. In fact, in the second example you could omit the return entirely and you would get the same behavior (the return would be implied as the function naturally completes and exits).
Without more of your function definition I can't say why you are getting a PSMethod object. My guess is that you probably have something a few lines up that is not being captured and is being placed on the output pipeline.
It is also worth noting that you probably don't need those semicolons - unless you are nesting multiple expressions on a single line.
You can read more about the return semantics on the about_Return page on TechNet, or by invoking the help return command from PowerShell itself.
This part of PowerShell is probably the most stupid aspect. Any extraneous output generated during a function will pollute the result. Sometimes there isn't any output, and then under some conditions there is some other unplanned output, in addition to your planned return value.
So, I remove the assignment from the original function call, so the output ends up on the screen, and then step through until something I didn't plan for pops out in the debugger window (using the PowerShell ISE).
Even things like reserving variables in outer scopes cause output, like [boolean]$isEnabled which will annoyingly spit a False out unless you make it [boolean]$isEnabled = $false.
Another good one is $someCollection.Add("thing") which spits out the new collection count.
With PowerShell 5 we now have the ability to create classes. Change your function into a class, and return will only return the object immediately preceding it. Here is a real simple example.
class test_class {
[int]return_what() {
Write-Output "Hello, World!"
return 808979
}
}
$tc = New-Object -TypeName test_class
$tc.return_what()
If this was a function the expected output would be
Hello World
808979
but as a class the only thing returned is the integer 808979. A class is sort of like a guarantee that it will only return the type declared or void.
As a workaround I've been returning the last object in the array that you get back from the function... It is not a great solution, but it's better than nothing:
someFunction {
$a = "hello"
"Function is running"
return $a
}
$b = someFunction
$b = $b[($b.count - 1)] # Or
$b = $b[-1] # Simpler
All in all, a more one-lineish way of writing the same thing could be:
$b = (someFunction $someParameter $andAnotherOne)[-1]
I pass around a simple Hashtable object with a single result member to avoid the return craziness as I also want to output to the console. It acts through pass by reference.
function sample-loop($returnObj) {
for($i = 0; $i -lt 10; $i++) {
Write-Host "loop counter: $i"
$returnObj.result++
}
}
function main-sample() {
$countObj = #{ result = 0 }
sample-loop -returnObj $countObj
Write-Host "_____________"
Write-Host "Total = " ($countObj.result)
}
main-sample
You can see real example usage at my GitHub project unpackTunes.
The existing answers are correct, but sometimes you aren't actually returning something explicitly with a Write-Output or a return, yet there is some mystery value in the function results. This could be the output of a builtin function like New-Item
PS C:\temp> function ContrivedFolderMakerFunction {
>> $folderName = [DateTime]::Now.ToFileTime()
>> $folderPath = Join-Path -Path . -ChildPath $folderName
>> New-Item -Path $folderPath -ItemType Directory
>> return $true
>> }
PS C:\temp> $result = ContrivedFolderMakerFunction
PS C:\temp> $result
Directory: C:\temp
Mode LastWriteTime Length Name
---- ------------- ------ ----
d----- 2/9/2020 4:32 PM 132257575335253136
True
All that extra noise of the directory creation is being collected and emitted in the output. The easy way to mitigate this is to add | Out-Null to the end of the New-Item statement, or you can assign the result to a variable and just not use that variable. It would look like this...
PS C:\temp> function ContrivedFolderMakerFunction {
>> $folderName = [DateTime]::Now.ToFileTime()
>> $folderPath = Join-Path -Path . -ChildPath $folderName
>> New-Item -Path $folderPath -ItemType Directory | Out-Null
>> # -or-
>> $throwaway = New-Item -Path $folderPath -ItemType Directory
>> return $true
>> }
PS C:\temp> $result = ContrivedFolderMakerFunction
PS C:\temp> $result
True
New-Item is probably the more famous of these, but others include all of the StringBuilder.Append*() methods, as well as the SqlDataAdapter.Fill() method.
You need to clear output before returning. Try using Out-Null. That's how powershell return works. It returns not the variable you wanted, but output of your whole function. So your example would be:
function Return-Url
{
param([string] $url)
. {
$rs = $url.ToString();
return
} | Out-Null
return $rs
}
$result = Return-Url -url "https://stackoverflow.com/questions/10286164/function-return-value-in-powershell"
Write-Host $result
Write-Host $result.GetType()
And result is:
https://stackoverflow.com/questions/10286164/function-return-value-in-powershell
System.String
Credits to https://riptutorial.com/powershell/example/27037/how-to-work-with-functions-returns
It's hard to say without looking at at code. Make sure your function doesn't return more than one object and that you capture any results made from other calls. What do you get for:
#($returnURL).count
Anyway, two suggestions:
Cast the object to string:
...
return [string]$rs
Or just enclose it in double quotes, same as above but shorter to type:
...
return "$rs"
Luke's description of the function results in these scenarios seems to be right on. I only wish to understand the root cause and the PowerShell product team would do something about the behavior. It seems to be quite common and has cost me too much debugging time.
To get around this issue I've been using global variables rather than returning and using the value from the function call.
Here's another question on the use of global variables:
Setting a global PowerShell variable from a function where the global variable name is a variable passed to the function
The following simply returns 4 as an answer. When you replace the add expressions for strings it returns the first string.
Function StartingMain {
$a = 1 + 3
$b = 2 + 5
$c = 3 + 7
Return $a
}
Function StartingEnd($b) {
Write-Host $b
}
StartingEnd(StartingMain)
This can also be done for an array. The example below will return "Text 2"
Function StartingMain {
$a = ,#("Text 1","Text 2","Text 3")
Return $a
}
Function StartingEnd($b) {
Write-Host $b[1]
}
StartingEnd(StartingMain)
Note that you have to call the function below the function itself. Otherwise, the first time it runs it will return an error that it doesn't know what "StartingMain" is.