use vars qw($change $alter);
$alter = 0;

sub readfile { while(<TEST>) {
    if ( $_ =~ /^\[ARTEC\]$/ )  {
               $alter = 1;
    exit print "found it exiting no need to change something";
          
        }else {
        $change = 1;
        print "n ";
        }        
    }
  return;
  } 
}
if ($alter == 0 and $change == 1) {
       #do something ...
	   print "changed\n";   
      
    }