Re^2: Using the Perl Debugger (-d)

Debug prints such as yours entail a runtime hit, which is almost always negligible; but they also clutter the code, which often isn't.

If you use something like this:

use constant DEBUG => 1;
print "Some useful information"
  if (DEBUG);
[download]

the compiler should optimize it away, which will remove even the small performance hit (or at least relegate it to the one-time compilation of the code).

--
sgifford's Web page

Comment on Re^2: Using the Perl Debugger (-d) Download Code

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Re^3: Using the Perl Debugger (-d) by MaxKlokan (Monk) on Jan 26, 2007 at 10:33 UTC
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;` [download] `use vars $d;` [download] `use vars qw/$d/; print "Debugging message..." if $d;` [download] Update To run the script you would use `perl myscript.pl -d`	[reply] [d/l] [select]
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;` [download] 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.	[reply] [d/l] [select]
Re^5: Using the Perl Debugger (-d) by BrowserUk (Patriarch) on Jan 26, 2007 at 12:09 UTC
Did you see Re: conditional debug call perf? Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply]


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