cddl/contrib/dtracetoolkit/Notes/ALLperl_notes.txt

   1 **************************************************************************
   2 * The following are notes for all the Perl tracing scripts,
   3 *
   4 * $Id: ALLperl_notes.txt 44 2007-09-17 07:47:20Z brendan $
   5 *
   6 * COPYRIGHT: Copyright (c) 2007 Brendan Gregg.
   7 **************************************************************************
   8
   9
  10 * Where did those "BEGIN" subroutine calls come from?
  11
  12 The following counts subroutines from the example program, Code/Perl/hello.pl,
  13
  14    # pl_subcalls.d
  15    Tracing... Hit Ctrl-C to end.
  16    ^C
  17     FILE                             SUB                                 CALLS
  18
  19 no subroutines were called, so there is no data to output.
  20
  21 Now a similar program is traced, Code/Perl/hello_strict.pl, which uses
  22 the "strict" pragma,
  23
  24    # pl_subcalls.d
  25    Tracing... Hit Ctrl-C to end.
  26    ^C
  27     FILE                             SUB                                 CALLS
  28     hello_strict.pl                  BEGIN                                   1
  29     strict.pm                        bits                                    1
  30     strict.pm                        import                                  1
  31
  32 not only were functions from "strict.pm" traced, but a "BEGIN" function
  33 ran from the "hello_strict.pl" program - which doesn't appear to use "BEGIN",
  34
  35    # cat -n ../Code/Perl/hello_strict.pl
  36         1  #!./perl -w
  37         2
  38         3  use strict;
  39         4
  40         5  print "Hello World!\n";
  41
  42 Perl appears to add a BEGIN block to process the "use" keyword. This makes
  43 some degree of sense.
  44