Let Perl generate the regular expression from a hash containing the list of words and their replacements: 
my %trans = (zero  => 0,
             one   => 1,
             two   => 2,
             three => 3);

my $words_re = join "|", map quotemeta, keys %trans;
$string =~ s/($words_re)/$trans{lc $1}/ig;

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In reply to Re: Combining multiple =~ s/ by salva
in thread Combining multiple =~ s/ by hennesse

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