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.
-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.