How to remove item from an array in PowerShell?

Question

I'm using Powershell 1.0 to remove an item from an Array. Here's my script:

param (
    [string]$backupDir = $(throw "Please supply the directory to housekeep"), 
    [int]$maxAge = 30,
    [switch]$NoRecurse,
    [switch]$KeepDirectories
    )

$days = $maxAge * -1

# do not delete directories with these values in the path
$exclusionList = Get-Content HousekeepBackupsExclusions.txt

if ($NoRecurse)
{
    $filesToDelete = Get-ChildItem $backupDir | where-object {$_.PsIsContainer -ne $true -and $_.LastWriteTime -lt $(Get-Date).AddDays($days)}
}
else
{
    $filesToDelete = Get-ChildItem $backupDir -Recurse | where-object {$_.PsIsContainer -ne $true -and $_.LastWriteTime -lt $(Get-Date).AddDays($days)}
}

foreach ($file in $filesToDelete)
{       
    # remove the file from the deleted list if it's an exclusion
    foreach ($exclusion in $exclusionList)
    {
        "Testing to see if $exclusion is in " + $file.FullName
        if ($file.FullName.Contains($exclusion)) {$filesToDelete.Remove($file); "FOUND ONE!"}
    }
}

I realize that Get-ChildItem in powershell returns a System.Array type. I therefore get this error when trying to use the Remove method:

Method invocation failed because [System.Object[]] doesn't contain a method named 'Remove'.

What I'd like to do is convert $filesToDelete to an ArrayList and then remove items using ArrayList.Remove. Is this a good idea or should I directly manipulate $filesToDelete as a System.Array in some way?

Thanks

Richard · Accepted Answer · 2010-02-26 14:42:26Z

9

The best way to do this is to use Where-Object to perform the filtering and use the returned array.

You can also use @splat to pass multiple parameters to a command (new in V2). If you cannot upgrade (and you should if at all possible, then just collect the output from Get-ChildItems (only repeating that one CmdLet) and do all the filtering in common code).

The working part of your script becomes:

$moreArgs = @{}
if (-not $NoRecurse) {
  $moreArgs["Recurse"] = $true
}

$filesToDelete = Get-ChildItem $BackupDir @moreArgs |
                 where-object {-not $_.PsIsContainer -and 
                               $_.LastWriteTime -lt $(Get-Date).AddDays($days) -and
                              -not $_.FullName.Contains($exclusion)}

In PSH arrays are immutable, you cannot modify them, but it very easy to create a new one (operators like += on arrays actually create a new array and return that).

edited Feb 26, 2010 at 14:42

answered Feb 26, 2010 at 11:37

Richard

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3 Comments

stej Over a year ago

(one typo PSIsContainere) Yes, I would prefer Where-Object as well. However in the question there are two loops - the inner goes through $exclusionList so the condition should probably be something like -not $($f=$_.Fullname; $exclusionList |?{$f.Contains($_)})

Mark Allison Over a year ago

Thanks Richard - can I use an string array for $exclusion. If you look closer at the code you will see that I would have to call get-childitem for every exclusion. This would not perform well if I have a lot of exclusions.

Richard Over a year ago

@MarkAllison: -exclude parameter takes a string[] so you can pass multiple wildcards.

stej · Accepted Answer · 2010-02-26 13:46:13Z

I agree with Richard, that Where-Object should be used here. However, it's harder to read. What I would propose:

# get $filesToDelete and #exclusionList. In V2 use splatting as proposed by Richard.

$res = $filesToDelete | % {
    $file = $_
    $isExcluded = ($exclusionList | % { $file.FullName.Contains($_) } )
    if (!$isExcluded) { 
        $file
    }
}

#the  files are in $res

Also note that generally it is not possible to iterate over a collection and change it. You would get an exception.

$a = New-Object System.Collections.ArrayList
$a.AddRange((1,2,3))
foreach($item in $a) { $a.Add($item*$item) }

An error occurred while enumerating through a collection:
At line:1 char:8
+ foreach <<<< ($item in $a) { $a.Add($item*$item) }
    + CategoryInfo          : InvalidOperation: (System.Collecti...numeratorSimple:ArrayListEnumeratorSimple) [], RuntimeException
    + FullyQualifiedErrorId : BadEnumeration

ZDNeal · Accepted Answer · 2016-02-22 18:33:20Z

This is ancient. But, I wrote these a while ago to add and remove from powershell lists using recursion. It leverages the ability of powershell to do multiple assignment . That is, you can do $a,$b,$c=@('a','b','c') to assign a b and c to their variables. Doing $a,$b=@('a','b','c') assigns 'a' to $a and @('b','c') to $b.

First is by item value. It'll remove the first occurrence.

function Remove-ItemFromList ($Item,[array]$List(throw"the item $item was not in the list"),[array]$chckd_list=@())
{

 if ($list.length -lt 1 ) { throw "the item $item was not in the list" }

 $check_item,$temp_list=$list
 if ($check_item -eq $item ) 
    {
      $chckd_list+=$temp_list
      return $chckd_list
    }
 else 
    {
     $chckd_list+=$check_item
     return (Remove-ItemFromList -item $item -chckd_list $chckd_list -list $temp_list )
    }
}

This one removes by index. You can probably mess it up good by passing a value to count in the initial call.

function Remove-IndexFromList ([int]$Index,[array]$List,[array]$chckd_list=@(),[int]$count=0)
{

 if (($list.length+$count-1) -lt $index )
  { throw "the index is out of range" }
 $check_item,$temp_list=$list
 if ($count -eq $index) 
  {
   $chckd_list+=$temp_list
   return $chckd_list
  }
 else 
  {
   $chckd_list+=$check_item
   return (Remove-IndexFromList -count ($count + 1) -index $index -chckd_list $chckd_list -list $temp_list )
  }
}

pberggreen · Accepted Answer · 2019-11-19 15:06:47Z

0

This is a very old question, but the problem is still valid, but none of the answers fit my scenario, so I will suggest another solution.

I my case, I read in an xml configuration file and I want to remove an element from an array.

[xml]$content = get-content $file
$element = $content.PathToArray | Where-Object {$_.name -eq "ElementToRemove" }
$element.ParentNode.RemoveChild($element)

This is very simple and gets the job done.

answered Nov 19, 2019 at 15:06

pberggreen

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