Okay, I fixed up the items you suggested I should, and so my script is looking like this: 
#!/usr/bin/perl 
use strict;
use warnings;


open my $fh, '<',"human_hg19_circRNAs_putative_spliced_sequence.fa",or
+ die $!;

my %id2seq;

    while(<$fh>){
        my $id = '';
        chomp;
        if($_ =~ /^>(.+)/){
            $id = $1;
        }else{
            $id2seq{$id} .= $_;
        }
    }

 

    foreach my $id (keys %id2seq){
        my $filename = (split /\|/, $id)[0];
        open  my $out_fh, '>>', "$filename" or die $!; 
        print $out_fh ">".$id."\n",$id2seq{$id}, "\n";
        close $out_fh;
    }


close $fh;

[download]

How do I integrate the value I've split and extracted into the naming of the file, because it's stating that it's uninitialised?

Although, I thought that it was clearly initialised/defined here: 

  my $filename = (split /\|/, $id)[0];
        open  my $out_fh, '>>', "$filename" or die $!;

[download]

Or maybe I'm just misunderstanding the scope? Where do I place the $filename in the loop?

Pete.

In reply to Re^4: An overlapping regex capture by Peter Keystrokes
in thread An overlapping regex capture by Peter Keystrokes

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