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

Hi,

I'm want some very simple logging that given something like 

file.pl
20: log_error( "a error msg", $level )

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prints the equivalent of doing this on the same line 
print STDERR "a error msg:" . __FILE__ .  __LINE__ 
if $level >= THRESHOLD;

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i.e. It prints the line number where the function was called, not the line number from inside the log_error subrountine.

Stuck on how to do this

1. Printing the line number where the log_error was called without including it in the argument

2. I'd like anything < THRESHOLDfor the current run to be removed at compile time if possible to avoid a performance hit...not sure if can really do that...or if it makes a difference.

This application has to be very fast I don't need much and prefer to not use any log modules if I don't need to.

Any help appreciated thanks so much!

Kosun

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Re: fast logging showing calling position..
by ikegami (Patriarch) on Sep 01, 2005 at 17:51 UTC
    1. Printing the line number where the log_error was called without including it in the argument

    The four Carp routines and the two Carp::Heavy routines provide this info (using caller).

    use Carp ();

sub log_error {
   goto(&Carp::carp) if pop(@_) >= THRESHOLD;
}

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    I think Log::Log4perl also prints the file name and the line number. The above and Log::Log4perl don't meet your second requirement, however.

     

    2. I'd like anything < THRESHOLD for the current run to be removed at compile time if possible to avoid a performance hit...not sure if can really do that...or if it makes a difference.

    That's not possible if the level is passed as an argument. Your syntax would have to be

    sub DEBUG     () { 0 }
sub FATAL     () { 4 }

sub THRESHOLD () { 0 }

log_error($msg) if FATAL >= THRESHOLD;

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    Well, either that or use a source filter.

     

    Maybe you could compile out debug messages, but leave the other ones in?

    use Carp ();

sub WARN  () { 1 }
sub ERROR () { 2 }

sub DEBUG     () { 0     }  # True of false.
sub THRESHOLD () { ERROR }  # Or use $THRESHOLD. No real diff.

sub log_error {
   my $level = (@_==2 ? pop(@_) : THRESHOLD);
   return if $level < THRESHOLD;
   goto &Carp::carp;
}

log_error($msg) if DEBUG;  # Whole statement removed at compile time.
log_error($msg, WARN);     # Calls log_error, but not carp.
log_error($msg, FATAL);    # Calls log_error and carp.

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Re: fast logging showing calling position..
by talexb (Chancellor) on Sep 01, 2005 at 19:20 UTC

    I can highly recommend Log::Log4perl. It matches your requirements very closely. I use it daily and it's terrific.

    Alex / talexb / Toronto

    "Groklaw is the open-source mentality applied to legal research" ~ Linus Torvalds

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