Why does this code not work?
$method = {
[System.Collections.ArrayList]$array;
for ($i=0; $i -le 50; $i++) { $array += $i }
}
Executing the scriptblock with:
&$method
Shows on the console:
1, 2, 3, 4, 5, 6
when it should print 50 numbers?
The Add() method of the ArrayList type emits the index at which a new item was inserted. Cast the expression to [void], pipe it to Out-Null or assign it to $null to supress this output:
[void]$array.Add($i)
# or
$array.Add($i) |Out-Null
# or
$null = $array.Add($i)
Avoid piping to Out-Null if you do this many times, casting or assigning is much faster than piping.
The code you posted shouldn't generate any output at all, unless you already have a variable $array defined in the parent scope. The statement
[System.Collections.ArrayList]$array
casts the value of the variable $array to the type ArrayList and echoes it. If the variable has a value in the parent scope the statement will output the value as an array list, otherwise the output will be null. The subsequent loop will not use that variable, but instead increment a new (local) variable $array. You can verify that by placing a statement $array.GetType().FullName at the end of the scriptblock. You'll get System.Int32, not System.Collections.ArrayList (or System.Object[]) as you might expect.
If you want to instantiate an ArrayList object, add numbers to it, and output that list at the end of the scriptblock, you need to change your code to something like this:
$method = {
[Collections.ArrayList]$array = #()
for ($i=0; $i -le 50; $i++) { $array += $i }
$array
}
Note the assignment operation in the first statement.
Demonstration:
PS C:\> $sb = { [Collections.ArrayList]$a; 0..50 | % { $a += $_ }; $a.GetType().FullName; $a }
PS C:\> &$sb
System.Int32
1275
PS C:\> $sb = { [Collections.ArrayList]$a = #(); 0..50 | % { $a += $_ }; $a.GetType().FullName; $a }
PS C:\> &$sb
System.Collections.ArrayList
0
1
...
49
50
My code looks like:
1..10 | % {
$i=$_
10..20 | % {
if ($_ -gt 12) {
continue
}
Write-Host $i $_
}
}
Why the output is:
1 10
1 11
1 12
It seems the continue statement in PoweShell is not different with other language, why PowerShell is designed like this?
If I change the continue to return, then I get the expect result.
As PeterSerAI pointed out in his comment, you don't use a loop in your code, you are instead using the Foreach-Object cmdlet which is different.
Just use a foreach loop instead:
foreach($obj in 1.. 10)
{
$i = $obj
foreach($obj2 in 10 ..20) {
if ($obj2 -gt 12) {
continue
}
Write-Host $obj $obj2
}
}
I'm trying to get something that looks like UNIX ls output in PowerShell. This is getting there:
Get-ChildItem | Format-Wide -AutoSize -Property Name
but it's still outputting the items in row-major instead of column-major order:
PS C:\Users\Mark Reed> Get-ChildItem | Format-Wide -AutoSize -Property Name
Contacts Desktop Documents Downloads Favorites
Links Music Pictures Saved Games
Searches Videos
Desired output:
PS C:\Users\Mark Reed> My-List-Files
Contacts Downloads Music Searches
Desktop Favorites Pictures Videos
Documents Links Saved Games
The difference is in the sorting: 1 2 3 4 5/6 7 8 9 reading across the lines, vs 1/2/3 4/5/6 7/8/9 reading down the columns.
I already have a script that will take an array and print it out in column-major order using Write-Host, though I found a lot of PowerShellish idiomatic improvements to it by reading Keith's and Roman's takes. But my impression from reading around is that's the wrong way to go about this. Instead of calling Write-Host, a script should output objects, and let the formatters and outputters take care of getting the right stuff written to the user's console.
When a script uses Write-Host, its output is not capturable; if I assign the result to a variable, I get a null variable and the output is written to the screen anyway. It's like a command in the middle of a UNIX pipeline writing directly to /dev/tty instead of standard output or even standard error.
Admittedly, I may not be able to do much with the array of Microsoft.PowerShell.Commands.Internal.Format.* objects I get back from e.g. Format-Wide, but at least it contains the output, which doesn't show up on my screen in rogue fashion, and which I can recreate at any time by passing the array to another formatter or outputter.
This is a simple-ish function that formats column major. You can do this all in PowerShell Script:
function Format-WideColMajor {
[CmdletBinding()]
param(
[Parameter(ValueFromPipeline)]
[AllowNull()]
[AllowEmptyString()]
[PSObject]
$InputObject,
[Parameter()]
$Property
)
begin {
$list = new-object System.Collections.Generic.List[PSObject]
}
process {
$list.Add($InputObject)
}
end {
if ($Property) {
$output = $list | Foreach {"$($_.$Property)"}
}
else {
$output = $list | Foreach {"$_"}
}
$conWidth = $Host.UI.RawUI.BufferSize.Width - 1
$maxLen = ($output | Measure-Object -Property Length -Maximum).Maximum
$colWidth = $maxLen + 1
$numCols = [Math]::Floor($conWidth / $colWidth)
$numRows = [Math]::Ceiling($output.Count / $numCols)
for ($i=0; $i -lt $numRows; $i++) {
$line = ""
for ($j = 0; $j -lt $numCols; $j++) {
$item = $output[$i + ($j * $numRows)]
$line += "$item$(' ' * ($colWidth - $item.Length))"
}
$line
}
}
}
In PowerShell v2, the following line:
1..3| foreach { Write-Host "Value : $_"; $_ }| select -First 1
Would display:
Value : 1
1
Value : 2
Value : 3
Since all elements were pushed down the pipeline. However, in v3 the above line displays only:
Value : 1
1
The pipeline is stopped before 2 and 3 are sent to Foreach-Object (Note: the -Wait switch for Select-Object allows all elements to reach the foreach block).
How does Select-Object stop the pipeline, and can I now stop the pipeline from a foreach or from my own function?
Edit: I know I can wrap a pipeline in a do...while loop and continue out of the pipeline. I have also found that in v3 I can do something like this (it doesn't work in v2):
function Start-Enumerate ($array) {
do{ $array } while($false)
}
Start-Enumerate (1..3)| foreach {if($_ -ge 2){break};$_}; 'V2 Will Not Get Here'
But Select-Object doesn't require either of these techniques so I was hoping that there was a way to stop the pipeline from a single point in the pipeline.
Check this post on how you can cancel a pipeline:
http://powershell.com/cs/blogs/tobias/archive/2010/01/01/cancelling-a-pipeline.aspx
In PowerShell 3.0 it's an engine improvement. From the CTP1 samples folder ('\Engines Demos\Misc\ConnectBugFixes.ps1'):
# Connect Bug 332685
# Select-Object optimization
# Submitted by Shay Levi
# Connect Suggestion 286219
# PSV2: Lazy pipeline - ability for cmdlets to say "NO MORE"
# Submitted by Karl Prosser
# Stop the pipeline once the objects have been selected
# Useful for commands that return a lot of objects, like dealing with the event log
# In PS 2.0, this took a long time even though we only wanted the first 10 events
Start-Process powershell.exe -Args '-Version 2 -NoExit -Command Get-WinEvent | Select-Object -First 10'
# In PS 3.0, the pipeline stops after retrieving the first 10 objects
Get-WinEvent | Select-Object -First 10
After trying several methods, including throwing StopUpstreamCommandsException, ActionPreferenceStopException, and PipelineClosedException, calling $PSCmdlet.ThrowTerminatingError and $ExecutionContext.Host.Runspace.GetCurrentlyRunningPipeline().stopper.set_IsStopping($true) I finally found that just utilizing select-object was the only thing that didn't abort the whole script (versus just the pipeline). [Note that some of the items mentioned above require access to private members, which I accessed via reflection.]
# This looks like it should put a zero in the pipeline but on PS 3.0 it doesn't
function stop-pipeline {
$sp = {select-object -f 1}.GetSteppablePipeline($MyInvocation.CommandOrigin)
$sp.Begin($true)
$x = $sp.Process(0) # this call doesn't return
$sp.End()
}
New method follows based on comment from OP. Unfortunately this method is a lot more complicated and uses private members. Also I don't know how robust this - I just got the OP's example to work and stopped there. So FWIW:
# wh is alias for write-host
# sel is alias for select-object
# The following two use reflection to access private members:
# invoke-method invokes private methods
# select-properties is similar to select-object, but it gets private properties
# Get the system.management.automation assembly
$smaa=[appdomain]::currentdomain.getassemblies()|
? location -like "*system.management.automation*"
# Get the StopUpstreamCommandsException class
$upcet=$smaa.gettypes()| ? name -like "*upstream*"
filter x {
[CmdletBinding()]
param(
[parameter(ValueFromPipeline=$true)]
[object] $inputObject
)
process {
if ($inputObject -ge 5) {
# Create a StopUpstreamCommandsException
$upce = [activator]::CreateInstance($upcet,#($pscmdlet))
$PipelineProcessor=$pscmdlet.CommandRuntime|select-properties PipelineProcessor
$commands = $PipelineProcessor|select-properties commands
$commandProcessor= $commands[0]
$null = $upce.RequestingCommandProcessor|select-properties *
$upce.RequestingCommandProcessor.commandinfo =
$commandProcessor|select-properties commandinfo
$upce.RequestingCommandProcessor.Commandruntime =
$commandProcessor|select-properties commandruntime
$null = $PipelineProcessor|
invoke-method recordfailure #($upce, $commandProcessor.command)
1..($commands.count-1) | % {
$commands[$_] | invoke-method DoComplete
}
wh throwing
throw $upce
}
wh "< $inputObject >"
$inputObject
} # end process
end {
wh in x end
}
} # end filter x
filter y {
[CmdletBinding()]
param(
[parameter(ValueFromPipeline=$true)]
[object] $inputObject
)
process {
$inputObject
}
end {
wh in y end
}
}
1..5| x | y | measure -Sum
PowerShell code to retrieve PipelineProcessor value through reflection:
$t_cmdRun = $pscmdlet.CommandRuntime.gettype()
# Get pipelineprocessor value ($pipor)
$bindFlags = [Reflection.BindingFlags]"NonPublic,Instance"
$piporProp = $t_cmdRun.getproperty("PipelineProcessor", $bindFlags )
$pipor=$piporProp.GetValue($PSCmdlet.CommandRuntime,$null)
Powershell code to invoke method through reflection:
$proc = (gps)[12] # semi-random process
$methinfo = $proc.gettype().getmethod("GetComIUnknown", $bindFlags)
# Return ComIUnknown as an IntPtr
$comIUnknown = $methinfo.Invoke($proc, #($true))
I know that throwing a PipelineStoppedException stops the pipeline. The following example will simulate what you see with Select -first 1 in v3.0, in v2.0:
filter Select-Improved($first) {
begin{
$count = 0
}
process{
$_
$count++
if($count -ge $first){throw (new-object System.Management.Automation.PipelineStoppedException)}
}
}
trap{continue}
1..3| foreach { Write-Host "Value : $_"; $_ }| Select-Improved -first 1
write-host "after"
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A while back I was reading about multi-variable assignments in PowerShell. This lets you do things like this
64 > $a,$b,$c,$d = "A four word string".split()
65 > $a
A
66 > $b
four
Or you can swap variables in a single statement
$a,$b = $b,$a
What little known nuggets of PowerShell have you come across that you think may not be as well known as they should be?
The $$ command. I often have to do repeated operations on the same file path. For instance check out a file and then open it up in VIM. The $$ feature makes this trivial
PS> tf edit some\really\long\file\path.cpp
PS> gvim $$
It's short and simple but it saves a lot of time.
By far the most powerful feature of PowerShell is its ScriptBlock support. The fact that you can so concisely pass around what are effectively anonymous methods without any type constraints are about as powerful as C++ function pointers and as easy as C# or F# lambdas.
I mean how cool is it that using ScriptBlocks you can implement a "using" statement (which PowerShell doesn't have inherently). Or, pre-v2 you could even implement try-catch-finally.
function Using([Object]$Resource,[ScriptBlock]$Script) {
try {
&$Script
}
finally {
if ($Resource -is [IDisposable]) { $Resource.Dispose() }
}
}
Using ($File = [IO.File]::CreateText("$PWD\blah.txt")) {
$File.WriteLine(...)
}
How cool is that!
A feature that I find is often overlooked is the ability to pass a file to a switch statement.
Switch will iterate through the lines and match against strings (or regular expressions with the -regex parameter), content of variables, numbers, or the line can be passed into an expression to be evaluated as $true or $false
switch -file 'C:\test.txt'
{
'sometext' {Do-Something}
$pwd {Do-SomethingElse}
42 {Write-Host "That's the answer."}
{Test-Path $_} {Do-AThirdThing}
default {'Nothing else matched'}
}
$OFS - output field separator. A handy way to specify how array elements are separated when rendered to a string:
PS> $OFS = ', '
PS> "$(1..5)"
1, 2, 3, 4, 5
PS> $OFS = ';'
PS> "$(1..5)"
1;2;3;4;5
PS> $OFS = $null # set back to default
PS> "$(1..5)"
1 2 3 4 5
Always guaranteeing you get an array result. Consider this code:
PS> $files = dir *.iMayNotExist
PS> $files.length
$files in this case may be $null, a scalar value or an array of values. $files.length isn't going to give you the number of files found for $null or for a single file. In the single file case, you will get the file's size!! Whenever I'm not sure how much data I'll get back I always enclose the command in an array subexpression like so:
PS> $files = #(dir *.iMayNotExist)
PS> $files.length # always returns number of files in array
Then $files will always be an array. It may be empty or have only a single element in it but it will be an array. This makes reasoning with the result much simpler.
Array covariance support:
PS> $arr = '127.0.0.1','192.168.1.100','192.168.1.101'
PS> $ips = [system.net.ipaddress[]]$arr
PS> $ips | ft IPAddressToString, AddressFamily -auto
IPAddressToString AddressFamily
----------------- -------------
127.0.0.1 InterNetwork
192.168.1.100 InterNetwork
192.168.1.101 InterNetwork
Comparing arrays using Compare-Object:
PS> $preamble = [System.Text.Encoding]::UTF8.GetPreamble()
PS> $preamble | foreach {"0x{0:X2}" -f $_}
0xEF
0xBB
0xBF
PS> $fileHeader = Get-Content Utf8File.txt -Enc byte -Total 3
PS> $fileheader | foreach {"0x{0:X2}" -f $_}
0xEF
0xBB
0xBF
PS> #(Compare-Object $preamble $fileHeader -sync 0).Length -eq 0
True
Fore more stuff like this, check out my free eBook - Effective PowerShell.
Along the lines of multi-variable assignments.
$list = 1,2,3,4
While($list) {
$head, $list = $list
$head
}
1
2
3
4
I've been using this:
if (!$?) { # if previous command was not successful
Do some stuff
}
and I also use $_ (current pipeline object) quite a bit, but these might be more known than other stuff.
The fact that many operators work on arrays as well and return the elements where a comparison is true or operate on each element of the array independently:
1..1000 -lt 800 -gt 400 -like "?[5-9]0" -replace 0 -as "int[]" -as "char[]" -notmatch "\d"
This is faster than Where-Object.
Not a language feature but super helpful
f8 -- Takes the text you have put in already and searches for a command that starts with that text.
Tab-search through your history with #
Example:
PS> Get-Process explorer
PS> "Ford Explorer"
PS> "Magellan" | Add-Content "great explorers.txt"
PS> type "great explorers.txt"
PS> #expl <-- Hit the <tab> key to cycle through history entries that have the term "expl"
Love this thread. I could list a ton of things after reading Windows Powershell in Action. There's a disconnect between that book and the documentation. I actually tried to list them all somewhere else here, but got put on hold for "not being a question".
I'll start with foreach with three script blocks (begin/process/end):
Get-ChildItem | ForEach-Object {$sum=0} {$sum++} {$sum}
Speaking of swapping two variables, here's swapping two files:
${c:file1.txt},${c:file2.txt} = ${c:file2.txt},${c:file1.txt}
Search and replace a file:
${c:file.txt} = ${c:file.txt} -replace 'oldstring','newstring'
Using assembly and using namespace statements:
using assembly System.Windows.Forms
using namespace System.Windows.Forms
[messagebox]::show('hello world')
A shorter version of foreach, with properties and methods
ps | foreach name
'hi.there' | Foreach Split .
Use $() operator outside of strings to combine two statements:
$( echo hi; echo there ) | measure
Get-content/Set-content with variables:
$a = ''
get-content variable:a | set-content -value there
Anonymous functions:
1..5 | & {process{$_ * 2}}
Give the anonymous function a name:
$function:timestwo = {process{$_ * 2}}
Anonymous function with parameters:
& {param($x,$y) $x+$y} 2 5
You can stream from foreach () with these, where normally you can't:
& { foreach ($i in 1..10) {$i; sleep 1} } | out-gridview
Run processes in background like unix '&', and then wait for them:
$a = start-process -NoNewWindow powershell {timeout 10; 'done a'} -PassThru
$b = start-process -NoNewWindow powershell {timeout 10; 'done b'} -PassThru
$c = start-process -NoNewWindow powershell {timeout 10; 'done c'} -PassThru
$a,$b,$c | wait-process
Or foreach -parallel in workflows:
workflow work {
foreach -parallel ($i in 1..3) {
sleep 5
"$i done"
}
}
work
Or a workflow parallel block where you can run different things:
function sleepfor($time) { sleep $time; "sleepfor $time done"}
workflow work {
parallel {
sleepfor 3
sleepfor 2
sleepfor 1
}
'hi'
}
work
Three parallel commands in three more runspaces with the api:
$a = [PowerShell]::Create().AddScript{sleep 5;'a done'}
$b = [PowerShell]::Create().AddScript{sleep 5;'b done'}
$c = [PowerShell]::Create().AddScript{sleep 5;'c done'}
$r1,$r2,$r3 = ($a,$b,$c).begininvoke()
$a.EndInvoke($r1); $b.EndInvoke($r2); $c.EndInvoke($r3) # wait
($a,$b,$c).Streams.Error # check for errors
($a,$b,$c).dispose() # cleanup
Parallel processes with invoke-command, but you have to be at an elevated prompt with remote powershell working:
invoke-command localhost,localhost,localhost { sleep 5; 'hi' }
An assignment is an expression:
if ($a = 1) { $a }
$a = $b = 2
Get last array element with -1:
(1,2,3)[-1]
Discard output with [void]:
[void] (echo discard me)
Switch on arrays and $_ on either side:
switch(1,2,3,4,5,6) {
{$_ % 2} {"Odd $_"; continue}
4 {'FOUR'}
default {"Even $_"}
}
Get and set variables in a module:
'$script:count = 0
$script:increment = 1
function Get-Count { return $script:count += $increment }' > counter.psm1 # creating file
import-module .\counter.psm1
$m = get-module counter
& $m Get-Variable count
& $m Set-Variable count 33
See module function definition:
& $m Get-Item function:Get-Count | foreach definition
Run a command with a commandinfo object and the call operator:
$d = get-command get-date
& $d
Dynamic modules:
$m = New-Module {
function foo {"In foo x is $x"}
$x=2
Export-ModuleMember -func foo -var x
}
flags enum:
[flags()] enum bits {one = 1; two = 2; three = 4; four = 8; five = 16}
[bits]31
Little known codes for the -replace operator:
$number Substitutes the last submatch matched by group number.
${name} Substitutes the last submatch matched by a named capture of the form (?).
$$ Substitutes a single "$" literal.
$& Substitutes a copy of the entire match itself.
$` Substitutes all the text from the argument string before the matching portion.
$' Substitutes all the text of the argument string after the matching portion.
$+ Substitutes the last submatch captured.
$_ Substitutes the entire argument string.
Demo of workflows surviving interruptions using checkpoints. Kill the window or reboot. Then start PS again. Use get-job and resume-job to resume the job.
workflow test1 {
foreach ($b in 1..1000) {
$b
Checkpoint-Workflow
}
}
test1 -AsJob -JobName bootjob
Emacs edit mode. Pressing tab completion lists all the options at once. Very useful.
Set-PSReadLineOption -EditMode Emacs
Any command that begins with "get-", you can leave off the "get-":
date
help
End parsing --% and end of parameters -- operators.
write-output --% -inputobject
write-output -- -inputobject
Tab completion on wildcards:
cd \pro*iles # press tab
Compile and import a C# module with a cmdlet inside, even in Osx:
Add-Type -Path ExampleModule.cs -OutputAssembly ExampleModule.dll
Import-Module ./ExampleModule.dll
Iterate backwards over a sequence just use the len of the sequence with a 1 on the other side of the range:
foreach( x in seq.length..1) { Do-Something seq[x] }