"fast and efficient" means, of course, Benchmark, which I'll leave up to you. Also, I'm not quite sure exactly how many is a "whole load". At some point this (or anything else, for that matter, everything has a breaking point) will fail. 

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1200434

use strict;
use warnings;
use re 'eval';

my $patterns = <<'END';
^\d{2}.\d{2}.\d{2}$      date
^\d{2}.\d{2}.\d{4}$      date
^[A-Z]{2}\d{9}[A-Z]{2}$  Royal Mail Track & Trace code
^\d{16}$                 visa card
^\d{13}$                 EAN-13 barcode
END

my $regex;

sub patternidentification
  {
  if( not defined $regex )
    {
    ##################### build a single regex just once

    my $all = join '|',
      map { /^(\S+)\s++(.+)/ ? "(?:$1(?{'$2'}))" : die "bad pattern $_
+" }
      split /\n/, $patterns;

    $regex = qr/$all/;
    }
  return /$regex/ ? $^R : "unknown";
  }


##################### then try all matches

while(<DATA>)
  {
  chomp;
  my $answer = patternidentification($_);
  print "$_ is a $answer\n";
  }

__DATA__
12 12 17
09 30 2O17
09 30 2017
09 30 12017
123123123123123
1231231231231231
12312312312312312
456456456456
4564564564567
45645645645678
QW123456789WQ

[download]

Outputs: 

12 12 17 is a date
09 30 2O17 is a unknown
09 30 2017 is a date
09 30 12017 is a unknown
123123123123123 is a unknown
1231231231231231 is a visa card
12312312312312312 is a unknown
456456456456 is a unknown
4564564564567 is a EAN-13 barcode
45645645645678 is a unknown
QW123456789WQ is a Royal Mail Track & Trace code

[download]

In reply to Re: Pattern Identification by tybalt89
in thread Pattern Identification by WhiteTraveller

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