# I have already read the 2-column table file into %table.
# I've also already opened INFILE and OUTFILE

my @keys_ordered = sort { length $table_ref->{$b} <=>
    length $table_ref->{$a} } keys %{$table_ref};
# Sorted in reverse order of length, so that longer strings
# in the data file are found before shorter strings
# Done here to increase speed, vs inside the while loop

my $replacecount = 0;
while ( my $line = <INFILE> ) {   
    for my $key ( @keys_ordered ) {
        $replacecount += ( $line =~ s/$key/$table_ref->{$key}/g );
    }
    print OUTFILE $line;
}    
print "Made $replacecount replacements.\n";