title: grep in all directories
body: <p>I have a directory named XYZ which has directories ABC, DEF, GHI inside it. I want to search for a pattern 'writeText' in all *.c in all directories (i.e XYZ, XYZ/ABC, XYZ/DEF and XYZ/GHI)
  What grep command can I use? </p>
  
  <p>Also if I want to search only in XYZ, XYZ/ABC, XYZ/GHI and not XYZ/DEF, what grep command can I use? </p>
  
  <p>Thank you! </p>