search a file for a pattern
-i     Perform  pattern  matching  in searches without regard to case; see the Base Definitions volume of
       IEEE Std 1003.1-2001, Section 9.2, Regular Expression General Requirements.
-n     Precede  each  output  line by its relative line number in the file, each file starting at line 1.
       The line number counter shall be reset for each file processed.
source manpages: grep