Hi, See following thread.
http://lists.gnu.org/archive/html/bug-grep/2009-05/msg00009.html > Grep 2.5.4 uses regex, which is included in GNU libc and supports > `\S' operand. However, Grep 2.5.4 also use own engines, which can't > interpret `\S' operand. So you mayn't use undocumented operands. `\s' is also the same as `\S'.
