print lines matching a pattern

--color[=WHEN], --colour[=WHEN]
       Surround the matched (non-empty) strings, matching lines, context lines, file names, line numbers,
       byte offsets, and separators (for fields and groups of context lines)  with  escape  sequences  to
       display  them  in  color  on  the  terminal.   The  colors are defined by the environment variable
       GREP_COLORS.  The deprecated environment variable GREP_COLOR is still supported, but  its  setting
       does not have priority.  WHEN is never, always, or auto.