use IO::File;

my %filehandle;
while (my ($k, $v) = associate_filename_with_values())
{
    $filehandle{$v} = IO::File->new(">$k")
        || die "Cannot open '$k' for writing\n";
}

my $data_fh = IO::File->new($datafile)
    || die "Cannot open '$datafile' for reading\n";

while (<$data_fh>)
{
    chomp;
    next unless length $_;
    my @line = split, /\s+/;

    my $value = $line[SOME_INDEX];
    $filehandle{$value}->print("$_\n");
}

$data_fh->close;
$_->close for values %filehandle;