Bulk file re-name with Groovy script

rename.groovy

// needed to rename over 900 files in a dir from a pattern like 
// noa_6989589000_201404080445010001.pdf to NAR6989589000.pdf where the 6989589000 part 
// (different on every file) is the needed in the new file.
// simply run from the CLI: groovy rename.groovy

dir = "/path to files"
def pre = "NAR", ext = ".pdf"
new File(dir).eachFile() { f ->
  def name = f.name.split('_')[1]
  f.renameTo("${pre}${name}${ext}")
}