Using a hash (or possibly an array), as suggested by other monks above, for storing file handles is the easiest solution.

Just remember that, in order to print to a filehandle stored in a hash you need to put the handle within curly brackets. For example, if %fh is your hash of filehandles and if your chromosome id is 5, the your need to do this: 

print {$fh{5}} "to be printed\n";

[download]

Another possible option to solve your problem is to use a dispatch table, i.e. to store in a hash anonymous functions printing to their own file handle (I have no environment on my mobile device to test this code right now). 

my %dispatch:
sub create_function {
    my $id = shift;
    open my $fh, ">", "file_nr_$id" or die "... $!";
    return sub { my $line = shift; print $fh $line; }
}

$dispatch{$_} = create_functions($_) for @list_of_chromosomes;

# ...
# later when reading the file, assuming you have obtained a $line and 
+an id $id from the input:
$dispatch{id}->($line);

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The create_function subroutine is something that is sometimes called a function factory; it generates anonymous subroutines which close over their own filehandle. This anonymous subroutines are returned to the caller and stored in the %dispatch hash. Then, when reading the input, you just call the anonymous subroutine stored in the hash.

In reply to Re: Opening multiple output files within a loop by Laurent_R
in thread Opening multiple output files within a loop by TJCooper

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