I answered a similar question recently with a loop: 

    $s =~ s/$_/$h{$_}/g for keys %h;

[download]

So I wondered how that would compare to your solution of combining the searches into a single regex. I thought your way might win for a few words, but surely with a lot of words the complexity of the regex would slow it down, right?

Well, so much for that theory. The Perl regex engine continues to amaze me. I gave it a pattern combining 676 strings (all two-letter combinations) with pipes like yours, and it blew the forloop method away (92 times faster). It also beat a regex solution using Regexp::Assemble, but I was using very simple and known search strings, so the hand-made pipe method was safe and simple. With unknown or more complex strings, making it harder to hand-make a safe and efficient search pattern, I think RA would probably come out on top eventually. Anyway, my test and results:

abaugher@bannor> cat 989705.pl 
#!/usr/bin/env perl
use Modern::Perl;
use Benchmark qw(:all);
use Regexp::Assemble;

my %h = map { $_ => uc } ( 'aa' .. 'zz' );
my $s = `cat bigfile`; # 8MB file

say "Testing with @{[-s 'bigfile']} byte file and @{[ scalar keys %h ]
+} patterns";

cmpthese( 10, {
        'forloop' => \&forloop,
        'pipes'   => \&pipes,
        'regexpa' => \&regexpa,
});

sub forloop {
        $s =~ s/$_/$h{$_}/g for keys %h;
}

sub pipes {
        my $p = join '|', keys %h;
        $s =~ s/($p)/$h{$1}/g;
}

sub regexpa {
        my $p = Regexp::Assemble->new->add(keys %h)->re;
        $s =~ s/($p)/$h{$1}/g;
}
abaugher@bannor> perl 989705.pl                               
Testing with 8560854 byte file and 676 patterns
              Rate forloop regexpa   pipes
forloop 9.75e-02/s      --    -96%    -99%
regexpa     2.40/s   2364%      --    -74%
pipes       9.08/s   9213%    278%      --

[download]

Aaron B.
Available for small or large Perl jobs; see my home node.

In reply to Re^2: multiple substitution by aaron_baugher
in thread multiple substitution by naturalsciences

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