Came to know that it can be done using classes, but is there a plain way to do it Any suggestions ???

Its unclear what a.pl and b.pl are and how you're running them, so maybe post code to explain that

You can use  $packagename::global = 12; to change the original

I suspect you might benefit from reading Tutorials: Simple Module Tutorial, Variable Scoping in Perl: the basics, Coping with Scoping , Mini-Tutorial: Perl's Memory Management, Lexical scoping like a fox, Of Symbol Tables and Globs,

I'm afraid I'm not sure what you're trying to do, but it looks like a.pl and b.pl are independent pieces of code importing the same module. Is this the case?

If that's so, then what you're trying to do is just not going to work - what you're trying to do is called inter process communication. Either writing it to a file and reading it back, or something similar. I can give a better example if that _is_ what you're trying to do. Do both a.pl and b.pl have to run concurrently, or do they run separately?

Otherwise - I tend to like to use subroutines and closures to move vars back and forth

{
  my $MASTERLOGFILE = "LOGFILE not defined";
  my $MASTERID = "00000000":
  sub get_masterid 
  {
    return $MASTERID;
  }

  sub set_masterid
  {
    ( $MASTERID ) = @_;
  }
}
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Exactly what I am trying to do. Both those scripts run separately and that is where I am getting the issue. Are you saying that, call a perl module to set the variable and use two functions to set the same ?

Then I'm afraid I have bad news - you cannot do what you're trying to do, the way you're trying to do it. A module is 'static' code - it's imported by your subs when you start them, but it doesn't have any persistent state.

You may wish to consider reading from a file. At the most basic this goes like (and please note - this is very basic, there's no error or integrity checking):

{ 
  my $state_file = "current_masterid.txt";
  my $MASTERLOGFILE;
  my $MASTERID;
  sub save_masterid
  {
    if ( defined $MASTERID ) 
    {
      open ( my $output_fh, ">", $state_file );
      print $output_fh $masterid;
      close ( $output_fh );
    }
  }
  
  sub load_masterid
  {
    if ( -f $state_file )
    {
      open ( my $input_fh, "<", $state_file );
      $MASTERID = <$input_fh>;
      close ( $input_fh );
    }
    else
    {
      $MASTERID = "00000000";
      $MASTERLOGFILE = "LOGFILE not defined";
      &save_masterid()
    }
  }
  
  sub get_masterid 
  {
    &load_masterid() unless defined $MASTERID;
    return $MASTERID;
  }
  
  sub set_masterid
  {
    ( $MASTERID ) = @_;
    &save_masterid();
  }
}
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