> Result: external grep wins hands-down. GNU regex loses hands-down. pcre 
quoted text
> seems to be better than glibc's regex engine, and gains ever so slightly 
> when using NO_MMAP.

Indeed GNU regex 0.12 loses, and that's why it was rewritten for (IIRC)
glibc 2.3.  Older glibc's use code derived from GNU regex 0.12; but the
old GNU regex code is dead in general (maybe it survives in Emacs -- but
I don't remember), and the glibc regex code can be used by external
programs via gnulib.

glibc is slower than PCRE mostly because it is internationalized.  So
for example it supports things like stra[.ss.]e matching both strasse
and stra