title: How to search-replace content within files in Ubuntu Linux?
body: <p>My platform:  Ubuntu linux workstation</p>
  
  <p>In a directory, I havea series of files, with file name xxx_1.in to xxx_50.in</p>
  
  <p>For each file, I want to replace abc to def.  If I do it individually, I should type :g/abc/s//def/g</p>
  
  <p>How to write a script to process all of the files at once?</p>