Path: utzoo!attcan!uunet!cs.utexas.edu!usc!ucsd!ucbvax!iwarp.intel.com!news
From: merlyn@iwarp.intel.com (Randal Schwartz)
Newsgroups: comp.lang.perl
Subject: Regexps (was Re: Changing the first character of a string.)
Message-ID: <1990Jul3.184351.3820@iwarp.intel.com>
Date: 3 Jul 90 18:43:51 GMT
References: <1990Jul3.144552.5407@uvaarpa.Virginia.EDU>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal Schwartz)
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
Lines: 48
In-Reply-To: worley@compass.com (Dale Worley)

In article <1990Jul3.144552.5407@uvaarpa.Virginia.EDU>, worley@compass (Dale Worley) writes:
| Also, this illustrates one thing I don't like about regexps -- people
| write code which depends on the order in which the alternatives are
| matched.

Regexps are well-defined and extremely predicatable about their
"leftmost wildcard matches the most possible iterations" behavior.
It's no more silly than presuming that "a" really matches "a", is it?

|	    For instance, in the regexp above, the case where [^\0]?
| matches the null string can always match, so it implicitly depends on
| the fact that the non-null match is tried first. 

Ugh.  It does this *by* *definition*.  No assumption necessary.

|						    On the other hand,
| it's hard (impossible?) to write a regexp which matches in only the
| right way without some way to specify context for the match (shades of
| \: and \;!!!).

It's probably durn near impossible, and an unnecessary burden on the
part of the programmer.  For example, what is the context for matching
/ab.*cd/ in the string "aaababfoocdcdce"?

I frequently run up against * and + matching a bit too much, and want
to "back it off" a bit, but have found the problem without general
solution.

For example, matching the first two-digit number in a line, discarding
all text before it.  I want to write:

	s/.*(\d\d)/\1/;

but instead am forced to do something like:

	/\d\d.*/; $_ = $&;

The first expression matches the *last* occurrance of two digits.  (I
know... the second one discards the newline... gimme a break.)

Regexps... your best friend... your worst enemy.  You decide. :-)

s//Just another Perl hacker,/; print
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
| merlyn@iwarp.intel.com ...!any-MX-mailer-like-uunet!iwarp.intel.com!merlyn |
\=Cute Quote: "Welcome to Portland, Oregon, home of the California Raisins!"=/