if ($you_do_not_want_script3_to_run) {
   # create zero byte size file...
   open(FAILFLAG, ">/tmp/script2.failflag") || do {
      # handle the error here
   };
   close (FAILFLAG);
}

##</code><code>##

my $script2_failflag = "/tmp/script2.failflag";
if (-e $script2_failflag) {
   # script3.pl should not contine any further
   exit();
}