On Sat, 19 Apr 2008, Jeff Johnson wrote:
A little reading indicates that I have inadvertently worded
my question re a PCRE <-> POSIX conversion "implementation"
incorrectly.
...
I was hoping that the _SYNTAX_ can be interconverted for a
significant subset of all possible PCRE <-> POSIX
expressions. I'm perfectly willing to try a imperfect, known
flawed, interconversion of _SYNTAX_ if the patterns that are
typically needed by RPM can be mostly converted reliably.
Note: "significant" and "typically needed". YMMV, as always.
I think this article encapsulates the issue I was noting in my
IRC remarks yesterday, mentioning classical Unix, FSF,
procmail <!>, and other varaints;
http://en.wikipedia.org/wiki/Regular_expression
[ Perl has a more predictable and much richer syntax than the
[ POSIX basic (BRE) and extended (ERE) regular expression
[ standards. ... other utilities ... have adopted syntax
[ similar to Perl's — for example ... PCRE ... [and others not
[ listed each] use regular expression syntax similar to Perl's
That is, there has been a 'pick and choose' over time, and of
course a series of 'improvements' and 'regularizations'
The implied requirement of a quest to find a prebuilt tool to
automatically do all possible inverse transforms, from the
initial use of the bare '<->', was probably doomed to 'no
reply' -- The article notes that there is an incompatible
even in the standard for simplest variation of POSIX 'basic'
and 'extended' forms:
[ The meaning of metacharacters escaped with a backslash is
[ reversed for some characters in the POSIX Extended Regular
[ Expression (ERE) syntax
so absent an option switch, no 'perfect' inverset (',-.') set
of transform can exist. Move a few generations away into PRCE
and ...
-- Russ herrold
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