Most useful grep Options

-h:   suppress file names in output
-w:   restrict search to whole words only
-c:   displays count of matching lines in each file, not the lines themselves
      (note this is not the same as $ grep index *.rb | wc -l)
-i:   ignore case
-l:   list only file names containing matching lines
-n:   precede each line with the line number where it was found
-v:   display all lines NOT matching pattern
-C:   Display NUM lines of context either side of matches
-B:   Display NUM lines of context Before the matches
-A:   Display NUM lines of context After the matches

-e pattern: 
      Search for a pattern. Can use multiple times on a line
-r:   Search recursively from the current or specificed directory
  --include=pattern:
      Only search in file names matching pattern
  --exclude=pattern:
      Do not search in file names matching pattern