Easy way to add a user as an administrator. Grants Farm Administrator rights along with ShellAdmin for Central Administration and a specified url.

add-spadmin.ps1

$username = "{username}"
$webAppUrl = "{url}"

$centralAdmin = Get-SPWebApplication -IncludeCentralAdministration | ?{$_.DisplayName -eq "SharePoint Central Administration v4"}

$caWeb = Get-SPWeb -Identity $centralAdmin.Url 
$farmAdministrators = $caWeb.SiteGroups["Farm Administrators"]
$farmAdministrators.AddUser($username, "", $username, "Configured via PowerShell")


$db = $centralAdmin.ContentDatabases[0]
Add-SPShellAdmin -UserName $username -database $db

Get-SPWebApplication $webAppUrl | Get-SPContentDatabase | ForEach-Object {
	Add-SPShellAdmin -UserName $username -database $_
}

Add-SPShellAdmin -UserName $username