SharePoint 2013: PowerShell to change site logo for all site collections/sites within a particular Web Application

Quick Post: You can use PowerShell in SharePoint 2013 to change the site logo for all site collections and sites within a particular web application. Copy/paste the following into a text file and rename it with a .ps1 extension.

$sitecollections = Get-SPSite -WebApplication http://webappurl ($sitecollections).AllWebs | foreach {$_.SiteLogoUrl = "/PublishingImages/logo.jpg"; $_.Update()}