To do this, you'd have to treat the string as a sort of base-n number where n is the number of possible characters you expect to find in the string. If you have flat seven bit ASCII, that's 128 characters. If you have Unicode encoding, it's some crazy huge number. If your alphabet is small, you can map each "letter" to a serial number to use as "digits."

Strings of even a modest length will be crazy huge when turned to numbers, so I don't think this will be useful for what you're trying to do.

use List::Util qw( sum );

my $s = 'ook';
my $base = 128;
my $e = 1/$base;
print sum map { ord() * ($e *= $base) } reverse split //, $s;
print "\n";
__END__
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Update: Fixed a bug—needed a call to reverse.