Better way to write this regex to match multi-ordered property list?

I've been whacking on this regex for a while, trying to build something that can pick out multiple ordered property values (DTSTART, DTEND, SUMMARY) from an .ics file. I have 开发者_如何学JAVAother options (like reading one line at a time and scanning), but wanted to build a single regex that can handle the whole thing.

SAMPLE PERL

# There has got to be a better way...
my $x1 = '(?:^DTSTART[^\:]*:(?<dts>.*?)$)';
my $x2 = '(?:^DTEND[^\:]*:(?<dte>.*?)$)';
my $x3 = '(?:^SUMMARY[^\:]*:(?<dtn>.*?)$)';
my $fmt = "$x1.*$x2.*$x3|$x1.*$x3.*$x2|$x2.*$x1.*$x3|$x2.*$x3.*$x1|$x3.*$x1.*$x2|$x3.*$x2.*$x1";

if ($evts[1] =~ /$fmt/smo) {
printf "lines:\n==>\n%s\n==>\n%s\n==>\n%s\n", $+{dts}, $+{dte}, $+{dtn};
} else {
print "Failed.\n";
}

SAMPLE DATA

BEGIN:VEVENT

UID:0A5ECBC3-CAFB-4CCE-91E3-247DF6C6652A

TRANSP:OPAQUE

SUMMARY:Gandalf_flinger1

DTEND:20071127T170005

DTSTART,lang=en_us:20071127T103000

DTSTAMP:20100325T003424Z

X-APPLE-EWS-BUSYSTATUS:BUSY

SEQUENCE:0

END:VEVENT

SAMPLE OUTPUT

lines:

==>

20071127T103000

==>

20071127T170005

==>

Gandalf_flinger1

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CPAN is your friend:

vFile

iCal parser

You will pull your hair out until bald without a parser on vFile format (other than trivial files.) Regex for this is very hard.

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Instead of permuting the three regexes into one big pattern with ORs, why not test the three patterns separately, since (given the anchoring $s, ) they cannot overlap?

my $x1 = qr/(?:^DTSTART[^:]*:(?<dts>.*?)$)/smo;
my $x2 = qr/(?:^DTEND[^:]*:(?<dte>.*?)$)/smo;
my $x3 = qr/(?:^SUMMARY[^:]*:(?<dtn>.*?)$)/smo;

if ($evts[1] =~ $x1 and $evts[1] =~ $x2 and $evts[1] =~ $x3)
{
    # ...
}

(I also turned the x variables into patterns themselves, and removed the unneeded escape in the character classes.)

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It's better to use three regexes and some extra logic. This problem isn't a good match for regexes.

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That's ugly... I think that the "better way" is to match each property, once at a time.