param( 
    [string]$url
)

function Add-Custom-Action($site, $actionUrl, $sequence)
{
    Write-Host "Add custom action $actionUrl on" $site.Url -foregroundcolor green
    $actions = $site.UserCustomActions
    $contains = $false
    foreach ($a in $actions)
    {
        #Write-Host "    " $a.ScriptSrc
        if ($a.ScriptSrc.ToLower() -eq $actionUrl.ToLower())
        {
            $contains = $true
            #$a.Delete()
            break
        }
    }
    
    if ($contains)
    {
        Write-Host "    Custom action is already added" -foregroundcolor yellow
        return
    }

    $action = $site.UserCustomActions.Add()
    $action.Location = "ScriptLink"
    $action.ScriptSrc = $actionUrl
    $action.Sequence = $sequence
    $action.Update();
}

if (-not $url)
{
    Write-Host "Specify site url in url parameter" -foregroundcolor red
    return
}

$webApp = Get-SPWebApplication $url
$webApp.Sites | ForEach-Object { Add-Custom-Action $_ "/_layouts/15/taloyhtio/scripts/CustomAction.js?v=20200511" 10001 }