ibanix has asked for the wisdom of the Perl Monks concerning the following question:

Greetings again, Monks,

I've got some code with a pretty simple debug routine. Not relevent parts of code not included. 
# Uncomment to enable writing debuging info to logfile
my $debug = 1;

# Open a debug logfile
if ($debug) {
    my $logfile = "movelog.debug.log";
    open(DEBUG, ">>$logfile");
    
    print DEBUG localtime().": Startup.\n";
}

if ($debug) { print DEBUG locasltime." : This is some example line...\
+n"; }

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This works well enough for me, but there are probally better ways to do it. Now to the real question:

How can I modify this for multiple levels of debug without having to radically alter my debug statements?

I'm thinking something like: 
my $debug = 2;

# This is level 2 information
if (something) { print DEBUG "LEVEL 2: foo\n"; }

# This is level 1 information
if (something) { print DEBUG "LEVEL 1: moo\n": }

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Where setting level 'n' would trigger all level 'n' and lower, from n-1 to level 0, debug output.

All advice appreciated! :-)

Cheers,
ibanix

$ echo '$0 & $0 &' > foo; chmod a+x foo; foo;

Replies are listed 'Best First'.
Re: Making debug a little more intelligent
by adrianh (Chancellor) on Dec 10, 2002 at 23:58 UTC

    You might want to take a look at one of the existing logging modules on CPAN. For example, Log::Log4perl, is fairly simple and gives you lots of flexibility.

    If you don't go that route I would consider using the constant module, rather than the lexical $debug. For example:

    use constant DEBUGGING => 2;
...
print DEBUG "foo\n" if DEBUGGING >=2;
...
print DEBUG "moo\n" if DEBUGGING;

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    The advantage of using the constant module is that the compiler can optimise out the debugging statements if DEBUGGING is false - potentially saving time and space.

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Re: Making debug a little more intelligent
by elusion (Curate) on Dec 10, 2002 at 23:35 UTC
    Here's what I'd use: 
    my $debug = 2;

sub debug {
    my ($level, $msg) = @_;
    return if $level > $debug;
    print DEBUG "LEVEL $level: $msg";
}

debug 2, "foo\n" if something;
debug 1, "moo\n" if something;

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    elusion : http://matt.diephouse.com

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Re: Making debug a little more intelligent
by traveler (Parson) on Dec 10, 2002 at 22:57 UTC
    I generally use something like 
    print LOG "message" if $debug <= 2;

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    Of course, I open the log and set the $| =1 in BEGIN. In one system, I do not open it if $debug == 0 and I close it/open it if the user changes $debug to/from 0 at runtime (which happens to be through a GUI).

    HTH, --traveler

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Re: Making debug a little more intelligent
by Mr. Muskrat (Canon) on Dec 10, 2002 at 23:00 UTC

    I'd use:

    my $debug = 2;

# This is level 3 information
if ($debug >= 3) { print DEBUG "LEVEL 3: bar\n"; }

# This is level 2 information
if ($debug >= 2) { print DEBUG "LEVEL 2: foo\n"; }

# This is level 1 information
if ($debug >= 1) { print DEBUG "LEVEL 1: moo\n"; }

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      I was going to do that, but it seemed so... like C. :-P

      That was a joke.

      $ echo '$0 & $0 &' > foo; chmod a+x foo; foo;
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      $debug and print
    1 == $debug ? "LEVEL 1: moo\n" :
    2 == $debug ? "LEVEL 2: foo\n" :
    "LEVEL 3: bar\n";

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      Makeshifts last the longest.

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Re: Making debug a little more intelligent
by vek (Prior) on Dec 11, 2002 at 13:57 UTC
    I usually use an environment variable to control debugging. This means I can do this in my code: 
    my $DEBUG = $ENV{DEBUG} || 0;

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    That way I don't have to worry about actually modifying the code in order to change how much debug info is logged.

    -- vek --
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