use warnings;
use strict;
my @errors;
for my $input (1..3) {       # main loop, just a demo
    # do something with $input here
    print "pattern$input\n";
    if ($input%2) {          # whatever your error condition is
       push @errors, "error$input";
    }
}
print "\n#errors\n";           # main loop over, now output @errors
for my $error (@errors) {
   print "$error\n";
}
print "cellpattern\n";