With LANG=C, one gets:
$ echo -e 'x y\nxsy'|grep 'x\(\s\)y'
which shows that \s matches s. But if we use a multibyte locale, or even a
complicated regexp, we get:
$ echo -e 'x y\nxsy'|grep 'x\(\s\|a\)y'
This inconsistency was analyzed by Flávio Leitner in bug #244768.
The behaviour of these regular expressions is undefined according to the GNU
grep documentation, and \s in undefined in POSIX BRE's and ERE's.
I believe the traditional behaviour was to match 's', thus it might be desirable
to maintain it, at least for C locale.
I forgot to mention the most important result of Flávio's analysis:
this is a symptom of an inconsistency between dfa.c and GNU regex (in libc):
dfa.c interprets '\s' as 's', while the GNU regex (is configured to?) interpret
it as a "space" character.
Based on the date this bug was created, it appears to have been reported
during the development of Fedora 8. In order to refocus our efforts as
a project we are changing the version of this bug to '8'.
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