On 03/11/2012 05:06 PM, Tim Landscheidt wrote: > Hi, > > the documentation for regexp says: > > | -- Builtin: regexp (STRING, REGEXP, [REPLACEMENT]) > | Searches for REGEXP in STRING. The syntax for regular expressions > | is the same as in GNU Emacs, which is similar to BRE, Basic > | Regular Expressions in POSIX. *Note Syntax of Regular > | Expressions: (emacs)Regexps. Support for ERE, Extended Regular > | Expressions is not available, but will be added in GNU M4 2.0. > > | [...] > > However: > > | [tim@passepartout ~]$ m4 > | regexp(`abc', `\(b\)') > | 1 > | regexp(`abc', `\(?:b\)') > | -1 > | [tim@passepartout ~]$ > > Emacs's documentation on "Backslash in Regular Expressions" > that is linked from m4's info file doesn't seem to imply > that shy groups were in fact ERE. So is this a bug?
Thanks for the report. Shy groups are not part of glibc's re_compile_pattern, and are therefore not a part of GNU m4. M4 is only using glibc's implementation with a flags of 0, which happens to be emacs-compatible, and not extensions such as shy groups that have later been added to just emacs beyond what glibc provides. If I could ever get more time to work on m4, there is a proposal for m4 2.0 to allow the user to have more control over which flavor of regex is in use, rather than forcing things to glibc's re_compile_pattern with the default flag settings. It would be feasible to make m4 2.0 compile against libpcre or other such extension mechanism, in order to also allow for additional regex flavors with features such as shy groups. -- Eric Blake ebl...@redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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