print lines matching a pattern

-l, --files-with-matches
       Suppress normal output; instead print the name of each input file from which output would normally
       have been printed.  The scanning will stop on the first match.  (-l is specified by POSIX.)

-R, -r, --recursive
       Read all files under each directory, recursively; this is equivalent to the -d recurse option.

Matcher Selection
    -E, --extended-regexp
           Interpret PATTERN as an extended regular expression (ERE, see below).  (-E is specified by POSIX.)

grep searches the named input FILEs (or standard input if no files are named, or if a single hyphen-minus
(-) is given as file name) for lines containing a match to the given PATTERN.  By  default,  grep  prints
the matching lines.

-i, --ignore-case
       Ignore case distinctions in both the PATTERN and the input files.  (-i is specified by POSIX.)