What's the best way to match against multiple, carefully-arranged alternative patterns and capture multiple matched subexpressions in a finite number of variables (in this case, two: $pfx and $num)?

(The truth is, I can't figure out how to ask the question I mean to ask. Please infer and interpret liberally and generously.)

I did this. I don't like it because it depends on esoteric regular expression stuff and because there are a bunch of repeated assignments to the same two variables. Is there a better way to accomplish the same parsing task?

$ cat parse_bates_numbers.pl
#!/usr/bin/perl
#
# parse_bates_numbers.pl

use strict;
use warnings;

$\ = "\n";
$, = "\t";

my ($pfx, $num);

while (my $bates_number = <DATA>) {
    chomp $bates_number;

    undef $pfx;
    undef $num;

    $bates_number =~ m{
        \A
        (?:
        # XYZ 999 99999999 or XYZ 99 ST 99999999 or XYZ 999 ST 9999999
+9
        (XYZ\s\d{2,3}(?:\sST)?) (?{ $pfx = $^N }) \s(\d{8})   (?{ $num
+ = $^N })
        |
        # XYZ U 999 99999999 or XYZ U 99 99999999 or XYZ V 9 99999999
        (XYZ\s[UV]\s\d{1,3})    (?{ $pfx = $^N }) \s(\d{8})   (?{ $num
+ = $^N })
        |
        # XYZ 99999999999
        (XYZ\s\d{3})            (?{ $pfx = $^N })   (\d{8})   (?{ $num
+ = $^N })
        |
        # XYZ 99999999 or XYZ 9999999
        (XYZ)                   (?{ $pfx = $^N }) \s(\d{7,8}) (?{ $num
+ = $^N })
        |
        # ABC-M-9999999
        (ABC-M-)                (?{ $pfx = $^N })   (\d{7})   (?{ $num
+ = $^N })
        |
        # ABCD-99999999
        (ABCD-)                 (?{ $pfx = $^N })   (\d{8})   (?{ $num
+ = $^N })
        |
        # 99999999999
        ()                      (?{ $pfx = $^N })   (\d{11})  (?{ $num
+ = $^N })
        )
        \z
    }x
        or die "Invalid Bates number $bates_number";

    print $bates_number, $pfx, $num + 0;
}

exit 0;

__END__
XYZ 123 00654321
XYZ 12 ST 00123456
XYZ 123 ST 00654321
XYZ U 123 00123456
XYZ U 12 00654321
XYZ V 1 00123456
XYZ 12300654321
XYZ 00123456
XYZ 0654321
ABC-M-0123456
ABCD-00654321
00000123456
$ perl ./parse_bates_numbers.pl | expand -20
XYZ 123 00654321    XYZ 123             654321
XYZ 12 ST 00123456  XYZ 12 ST           123456
XYZ 123 ST 00654321 XYZ 123 ST          654321
XYZ U 123 00123456  XYZ U 123           123456
XYZ U 12 00654321   XYZ U 12            654321
XYZ V 1 00123456    XYZ V 1             123456
XYZ 12300654321     XYZ 123             654321
XYZ 00123456        XYZ                 123456
XYZ 0654321         XYZ                 654321
ABC-M-0123456       ABC-M-              123456
ABCD-00654321       ABCD-               654321
00000123456                             123456
$

[download]
Also, why do I have to declare the variables $pfx and $num outside the while loop for this to work properly?

Jim

In reply to Matching Multiple Alternative Patterns and Capturing Multiple Subexpressions by Jim

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.