PowerShell - Iterate through all webs, then iterate through all lists , then add a column where a list is a certain name

Question

I'm trying to put together a script that should iterate through all webs in a site collection, then iterate through all lists in those webs, then add a column where a list has a certain name.

This is what I have so far:

[CmdletBinding()]
Param
(
[Parameter(Mandatory=$True,Position=1)]
[string]$sc
)

$spsite = Get-SPsite $sc 

foreach ($web in $spsite.AllWebs)
{   
        foreach ($list in $spsite.AllWebs)
        {
            $splist = $list.Lists["PSList"]
            $splist.Fields.Add("Calc", "Calculated", 0)
            $spfield = $splist.Fields.Getfield("Calc")
            $spfield.formula = "=TEXT([Start Date],`"mm/dd/yyyy`")`&`" - `"`&TEXT([End Date],`"mm/dd/yyyy`")"
            $spfield.outputtype = "Text"
            $spfield.update()
        }
}
$spsite.dispose()

This is the error I get:

You cannot call a method on a null-valued expression. At C:\scripts\addcalc.ps1:24 char:22 + $splist.Fields.Add <<<< ("Calc", "Calculated", 0) + CategoryInfo : InvalidOperation: (Add:String) [], RuntimeException + FullyQualifiedErrorId : InvokeMethodOnNull

I'm sure it's because I'm not iterating through the webs and then through the lists property. What's the correct way to achieve what I'm trying to do?

Answer 1

First - you must delete foreach ($list in $spsite.AllWebs) then find list using

$list = $web.Lists["InternalNameOfTheList"]

or

$list = $web.GetList($web.Url + "/Lists/" + $ListName) and after that add column using

$spFieldType = [Microsoft.SharePoint.SPFieldType]::Text //change to your field type

$list.Fields.Add("YourColumn",$spFieldType,$false)
$list.Update()

And dispose SPWeb object after using it, like you do for SPSite object .

Answer 2

Thanks Andrey. Your suggestion led me down the right path. Here's the final working version of the script that solves the original question.

[CmdletBinding()]
Param(
  [Parameter(Mandatory=$True,Position=1)]
   [string]$sc
)
$site = Get-SPSite $sc
$webs = Get-SPWeb $sc
$count = 0
foreach ($web in $site.AllWebs)
{   
            if (($webs.Count -le $Count) -and ($list = $web.Lists["PSList"]))
            {   

                $list.Fields.Add("Calc", "Calculated", 0)
                $field = $list.Fields.Getfield("Calc")
                $field.formula = "=TEXT([Start Date],`"mm/dd/yyyy`")`&`" - `"`&TEXT([End Date],`"mm/dd/yyyy`")"
                $field.outputtype = "Text"
                $field.update()
            }           
$count ++       
}
$site.dispose()
$webs.dispose()