open PS, "ps -A |";
   # Note: not all versions of ps use the same args;
   #     -A works on Linux systems, but you may need
   #     -x on some systems, e.g., Darwin.
   my @instance = grep { /abcd/ } <PS>;
   print "Running Instances:\n";
   print join "\n", map { "\t$_" } @instances;
   print "\n";