sigh, i misunderstood how mysql was escaping newline and tab. the following code properly reads the file output by mysqldump (although it may not be the most efficient):

    my $line = '';
    while (<$in>) {
        $line .= $_;
        next if m/\\$/;
        chomp $line;
        my @cols = ('');
        my @tabs = split /\t/, $line;
        foreach (@tabs) {
            $cols[$#cols] =~ m/\\$/ and do {
                $cols[$#cols] .= "\t$_";
                next;
            };
            push @cols, $_;
        }
        shift @cols;
                <processing done here>
        $line = '';
    }
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