my %id2seq = ();
my $id = '';

open File,"human_hg19_circRNAs_putative_spliced_sequence.fa",or die $!;

    while(<File>){
        chomp;
        if($_ =~ /^>(.+)/){
            $id = $1;
        }else{
            $id2seq{$id} .= $_;
        }
    }
my $filename = "'$id'";
open  (my $fh, '>', $filename) or die "Could not open '$filename' $!"; 

    foreach $id (keys %id2seq){
        print $fh ($id."\n",$id2seq{$id}, "\n");
    }



close File;
close $fh;