in reply to Re^2: Using the Perl Debugger (-d)
in thread Using the Perl Debugger (-d)

I have used your same approach sometimes. The problem I hit is that if your program has been migrated to a production environment where the script is read-only, you cannot turn on/off the switch for debugging purposes.
That is why I prefer to add a command-line switch to turn on debugging: 
#!/usr/bin/perl -s
use warings
use strict;

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use vars $d;

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use vars qw/$d/;

print "Debugging message..." if $d;

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Update
To run the script you would use perl myscript.pl -d

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Re^4: Using the Perl Debugger (-d)
by bart (Canon) on Jan 26, 2007 at 11:59 UTC
    I'm sure it must be feasable to set the value for the constant based on a command line switch. I'm not sure if one can just plug in use a module like Getopt::Std or Getopt::Long for this — they probably work at runtime, and might interfere with your own use of command line switches. Hence the handcrafted code, in the example: 
    {
   my $debug;
   BEGIN {
       if(grep { $_ eq '-d' } @ARGV) {          # look for switch
           $debug = 1;
           @ARGV = grep { $_ ne '-d' } @ARGV;  # remove switch
       }
   }
   use constant DEBUG => $debug;
}

print "Debug is on" if DEBUG;

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    Does anybody else get a "Useless use of a constant in void context" warning for the print line if DEBUG is off, or is it my old Perl version (5.6.1)? -MO=Deparse tells me it got replaced by the statement '???';, which might explain it. It's still silly.

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