# config:
my $field = 0;
my $sep = "\t";




$, = $sep;
$\ = $/;

my %file; # { ID, sequence, $fh }

my $fID = 1;

while (<INFILE>)
{
	chomp;
	my @c = split /$sep/o;

	my( $key, $ID ) = defined $c[$field]
		? ( $c[$field], $fID++ )
		: ( '(column not present)', 0 );

	unless ( $file{$key} )
	{
		$file{$key}{ID} = $ID;
		$file{$key}{sequence} = sprintf '%03d.tabular', $file{$key}{ID};
		-f $file{$key}{sequence} and die
			"Sorry, '$file{$key}{ID}' exists; won't clobber."; 
		open $file{$key}{fh}, ">", $file{$key}{sequence} or die
			"Error opening '$file{$key}{sequence}' for write - $!";
	}

	print {$file{$key}{fh}} @c;
}

print OUTFILE $file{$_}{sequence}, $_
	for sort { $file{$a}{ID} <=> $file{$b}{ID} } keys %file;