2016-11-18 08:48:04 -0800, Paul Eggert: > Stephane Chazelas wrote: > >Why would it make it slower. AFAICT, PCRE_MULTILINE *adds* > >some overhead. > > As I understand it, PCRE_MULTILINE lets 'grep' apply a pattern to an > entire buffer that contains many lines, and this lets PCRE > efficiently find the first match in the whole buffer. If grep > doesn't use PCRE_MULTILINE, grep would have to apply the pattern to > each line separately, which could be significantly slower. [...]
That might have been the case a long time ago, as I remember some discussion about it as it explained some wrong information in the documentation, but as far as I and gdb can tell, grep 2.26 at least call pcre_exec for every line of the input with grep -P. If it didn't echo test | grep -P '\n$' would match. I'll try and dig up the old discussions. -- Stephane
