I would like to have a function to run different ScriptBlocks. So, I need to use my Scriptblock as the parameter of the function. It does not work.
For example. This function returns the ScriptBlock as a string.
function Run_Scriptblock($SB) {
return $SB
}
These are the outputs from my tries:
# 1st try
Run_Scriptblock {systeminfo}
>> systeminfo
# 2nd try
Run_Scriptblock systeminfo
>> systeminfo
# 3rd try
Run_Scriptblock [scriptblock]systeminfo
>> [scriptblock]systeminfo
# 4th try
$Command = [scriptblock]{systeminfo}
Run_Scriptblock $Command
>> [scriptblock]systeminfo
# 5th try
[scriptblock]$Command = {systeminfo}
Run_Scriptblock $Command
>> systeminfo
If you want a function to run a scriptblock, you need to actually invoke or call that scriptblock, i.e.
function Run_Scriptblock($SB) {
$SB.Invoke()
}
or
function Run_Scriptblock($SB) {
& $SB
}
Otherwise the function will just return the scriptblock definition in string form. The return keyword is not needed, since PowerShell functions return all non-captured output by default.
The function would be called like this:
Run_Scriptblock {systeminfo}
As a side note, I would recommend you consider naming your function following PowerShell conventions (<Verb>-<Noun> with an approved verb), e.g.
function Invoke-Scriptblock($SB) {
...
}
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.
I am really new to Powershell but I have programmed in Java and other languages.
I am trying to pass a string to a function and then have that function return the string. Below is the simple code I am trying to run:
#funcpass.ps1
function test {
Param([string]$input)
$out = $input
return $out
}
$a = test hello world
Write-Host $a
I expect this to pass the string hello world then return the string into the variable $a to be printed. Instead my console returns this:
PS P:\test> .\funcpass.ps1
PS P:\test>
Is there some kind of scope error that I am encountering? Any help would be greatly appreciated. I am not sure if the version number helps, but here it is:
PS P:\test> $PSVersionTable.PSVersion
Major Minor Build Revision
----- ----- ----- --------
5 1 14393 1198
The $input parameter is reserved, so you have to change its name. Moreover, if you want to pass only one string to the function you have to enclose it with quotes:
function Run-Test {
Param([string]$inputValue)
$out = $inputValue
return $out
}
$a = Run-Test "hello world"
Write-Host $a
FYI the return keyword is optional but it makes your intentions more clear as other language use return to indicate that something is being returned from the function. Everything sent on the pipeline inside the function (like Write-Output) will be returned.
Say I have this simple PowerShell function:
function testit() {
return $true > $null
}
Write-Host "testing"
$thistest = testit
Write-Host "value = $thistest"
When I use it in my PowerShell script, I want to receive the value in the script but I don't want it to show in the console.
How do I keep the return value in the pipeline but just hide it from console?
If I use the > $null then it suppresses the output completely - I just want it to not show in the console, but I still want the value.
As documented PowerShell functions return all non-captured output to the caller. If the caller doesn't do anything with the returned value PowerShell automatically passes it to Out-Default, which then forwards it to Out-Host (see this article written by Don Jones).
Using redirection operators on the return value inside the function effectively suppresses the return value so that the function wouldn't return anything.
If you have a function like this:
function testit {
return $true
}
and call it by itself:
testit
PowerShell implicitly does this:
testit | Out-Default
which effectively becomes
testit | Out-Host
If you capture the return value in a variable
$thistest = testit
the value gets stored in the variable without anything being displayed on the console.
If you redirect the output or pipe it into Out-Null
testit >$null
testit | Out-Null
the return value is discarded and nothing is displayed on the console.
If you want to prevent PowerShell's default behavior of passing uncaptured output at the end of a pipeline to Out-Host you can do so by overriding Out-Default like this:
filter Out-Default { $_ | Out-Null }
or (as #PetSerAl pointed out in the comments) like this:
filter Out-Default {}
However, beware that this modification disables Out-Default for everything in the current scope until you remove the filter again. If you do for instance a Get-ChildItem while the filter is active nothing will be displayed unless you explicitly write the output to the host console:
Get-ChildItem | Out-Host
You remove the filter like this:
Remove-Item function:Out-Default