SharePoint: Add Content Type Fields

Add-SPContentTypeField.ps1

function Add-SPContentTypeField
{
    <#
        .Synopsis
            This function will allow you to add a library field to a Content Type
        .Description
            This function will add the nominated site column/ library column to a nominated Content Type 
            within all of the 'Document Libraries' in the given Site Collection
        .Example
            C:\> Add-SPContentTypeField –SiteUrl “http://yourdomain.com/sites/Finance –FieldName "myField" -CTypeAddedTo "myContentType"
        .Notes
            Name: Add-SPContentTypeField
            Author: Petro Margaritis
            Last Edit: 19/07/2012
            Keywords: Fields, Site Columns, Content Types
        .Link
            http://www.iampetro.com/
    #>

    Param (
        [parameter(Mandatory=$true)][string]$SiteUrl,
        [parameter(Mandatory=$true)][string]$FieldName,
        [parameter(Mandatory=$true)][string]$CTypeAddedTo
    )

    $site = Get-SPSite $SiteUrl

    # Walk through each site in the site collection
    $site | Get-SPWeb -Limit all | ForEach-Object {

        write-host "Checking site:"$_.Title -Foregroundcolor Green

        # Go through each document library in the site
        foreach ($list in $_.Lists | where { $_.BaseTemplate -eq "DocumentLibrary" })
        {

            # Check to see if the library contains the content type we are looking for
            if (($list.ContentTypes | where { $_.Name -eq $CTypeAddedTo }) -eq $null)
            {
                Write-Host "The Content:" $CTypeAddedTo "does not exist in the library:" $list.Title -Foregroundcolor Red
            } 
            else 
            {
                # Check to see if the library contains the field we are looking for
                if (($list.Fields | where { $_.Title -eq $FieldName }) -ne $null)
                {
                    # Get the content type you want to add the field to
                    $ct = $list.ContentTypes[$CTypeAddedTo]
                    # Get the column you want to copy
                    $field = $list.Fields[$FieldName]
                    # Add the column to the content type
                    $ct.Fieldlinks.Add($field)
                    $ct.update()

                    # Add additional column settings
                    $ctFieldLinks = $ct.FieldLinks | Where {$_.Name -eq $field.Title}
                    # OPTIONAL: This will set the column to hidden so that it is not viewable in the edit form
                    $ctFieldLinks.Hidden = $true
                    # Set Field to require value
                    $ctFieldLinks.Required = $true
                    $ct.Update()
                    Write-Host "The Field:" $field.Title "has been successfully added to the library:" $list.Title -Foregroundcolor Cyan
                }
                else
                {
                    Write-Host "The Field:" $FieldName "does not exist in the library:" $list.Title -Foregroundcolor Yellow
                }
            }
        }
    }
    # Dispose of the site object
    $site.Dispose()
}