print lines matching a pattern

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

Other Options
    --line-buffered
           Use line buffering on output.  This can cause a performance penalty.

    -C NUM, -NUM, --context=NUM
           Print NUM lines of output context.  Places a  line  containing  a  group  separator  (--)  between
           contiguous  groups  of  matches.   With the -o or --only-matching option, this has no effect and a
           warning is given.

File and Directory Selection
    -a, --text
           Process a binary file as if it were text; this is equivalent to the --binary-files=text option.