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From: Christopher Rued <c.rued@xsb.com>
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Message-ID: <14808.63902.442934.667120@chris.xsb.com>
Date: Mon, 2 Oct 2000 17:09:50 -0400 (EDT)
To: "Andresen,Jason R." <jandrese@mitre.org>
Cc: Mark Ovens <marko@FreeBSD.ORG>,
	Christopher Rued <c.rued@xsb.com>, freebsd-questions@FreeBSD.ORG
Subject: Re: Perl question
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Andresen,Jason R. writes:
 > > BTW, your RE should have a ``*'' as well:
 > > 
 > >         /x.*?y/
 > > 
 > 
 > Maybe, it depends on exactly what he was trying to get.
 > 
 > The first 3 character match where x and y are the first and third
 > character respectivly, then x.y is exactly what you want.  The smallest
 > set of characters that have x and y as boundry values?  Then your x.*?y
 > is correct.  The smallest set of characters that have x and y as
 > boundries and have at least one character in between them?  x.+?y is
 > needed.

The RE I used was precisely what I wanted: x.y (an `x' followed by
exactly one character followed by a `y').

When I run the following:

    #!/usr/bin/perl
    $a = "xayxbyxcyxdy";
    @s = $a =~ /x.y/;
    print "\@s is @s\n";

I get:
   
    @s is 1



So, I seem to be getting the truth value rather than the first match
in the string.  If, however, I wrap the entire RE in a parentheses
(make it a subexpression) like so:

    #!/usr/bin/perl
    $a = "xayxbyxcyxdy";
    @s = $a =~ /(x.y)/;
    print "\@s is @s\n";

I get the results I wanted to begin with:

    @s is xay

(I discovered this shortly after I sent the first message about this).



What confuses me is that if I specify the global option, I do not need
to use a subexpression.  For example, if I run the following code:

    #!/usr/bin/perl
    $a = "xayxbyxcyxdy";
    @s = $a =~ /x.y/g;
    print "\@s is @s\n";

I get:

    @s is xay xby xcy xdy


So, this leaves me with a couple of questions, the main one being:
  Why the different treatment for single matches and global
  matches?

and a less important one:
  Why is there no way to have the first match assigned to a scalar,
  since we can be sure that there will be at most one match returned?



If anyone can explain this, and/or answer the questions posed above,
I'd appreciate it.

						-Chris


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