title: powershell rename all files in a folder to a pattern
body: <p>I am very new to powershell. I have a folder with multiple files, each file name is like:</p>
  
  <p>File1_backup_2016_09_01_095444_1628350.bak</p>
  
  <p>Need to rename all of them to Filex_yyyymmdd.bak</p>