Hi, I have a collection of patterns (actually just keywords). For a given input string, I'd like to find out the number of matches for each of the keywords. A simple solution is as follows:

use strict;

my @keywords=qw/foo bar 12345 abcd/;
my $string = "foobarfoo1234523423412345abcdefsadfabc";
my %result;
foreach my $k (@keywords){
  my @matches = ($string =~ /$k/ig );
  $result{$k} = scalar(@matches);
}

foreach my $s (keys %result){
  print "$s=>$result{$s}\n";
}

__END__
bar=>1
12345=>2
foo=>2
abcd=>1
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Now my problem is that the array @keywords can be big (~ 10000), and the string can be pretty long. The above method goes through the string many times (same as @keywords), I'd like to make it more efficient by going through it, say once. One step in that direction is probably concat a long expression:

  $pattern = join("|", @keywords);
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but how do I get the count? Are there other ways (e.g., construct explicitly some kind of DFA) to do this? Thanks.

20041208 Edit by castaway: Changed title from 'Count mutliple pattern matches'