How about like this: 

#!/usr/bin/perl
use warnings;
use strict;

my $old_string = 'the dog chased my cat.';

my %dict;
while ( <DATA> ) {
    my ( $key, $val ) = /^(\d+)\s+(\w+)/;
    $dict{ $val } = $key;
    }

my $cc = join '', keys %dict;
my ( $min ) = my ( $max ) = map length, keys %dict;
for ( map length, keys %dict ) {
    $min = $_ if $min > $_;
    $max = $_ if $max < $_;
    }

my $pattern = qr/\b([$cc]{$min,$max})\b/;

( my $new_string = $old_string ) =~ s/$pattern/ exists $dict{ $1 } ? $
+dict{ $1 } : $1 /eg;

print "$old_string\n$new_string\n";


__DATA__
1 dog
2 cat
3 chased
4 the

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In reply to Re^2: search and replace by jwkrahn
in thread search and replace by Anonymous Monk

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