while(
defined(my $head = <FASTQIN>) &&     
defined(my $seq = <FASTQIN>) &&      
defined(my $qhead = <FASTQIN>) &&    
defined(my $quality = <FASTQIN>)     
){
  substr($head, 0, 1, '>'); 
  my $temp = print $head, $seq;
}
  close (FASTQIN);  

my %count_seq;
    open my $fh, '<:encoding(UTF-8)', $temp or die "Cannot open $temp $!";
    while (<$fh>) { 
        chomp;
        next if /^>/;   		     	    
        next if length($_) > 30 or length($_) < 15; 
        $count_seq{$_}++;  			    
    }

##</code><code>##

Use of uninitialized value $temp in open at test.pl line 44.
Use of uninitialized value $temp in concatenation (.) or string at test.pl line 44.
Cannot open  No such file or directory at test.pl line 44.

##</code><code>##

open my $fh, '<:encoding(UTF-8)', $temp or die "Cannot open $temp $!";