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Manual Reference Pages  -  LOG::TRACEMESSAGES (3)

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Log::TraceMessages - Perl extension for trace messages used in debugging



  use Log::TraceMessages qw(t d);
  $Log::TraceMessages::On = 1;
  t got to here;
  t value of $a is  . d($a);
      local $Log::TraceMessages::On = 0;
      t this message will not be printed;

  $Log::TraceMessages::Logfile = log.out;
  t this message will go to the file log.out;
  $Log::TraceMessages::Logfile = undef;
  t and this message is on stderr as usual;

  # For a CGI program producing HTML
  $Log::TraceMessages::CGI = 1;

  # Or to turn on trace if theres a command-line argument --trace


This module is a slightly better way to put trace statements into your code than just calling print(). It provides an easy way to turn trace on and off for particular sections of code without having to comment out bits of source.


$Log::TraceMessages::On Flag controlling whether tracing is on or off. You can set it as you wish, and of course it can be local-ized. The default is off.
$Log::TraceMessages::Logfile The name of the file to which trace should be appended. If this is undefined (which is the default), then trace will be written to stderr, or to stdout if $CGI is set.
$Log::TraceMessages::CGI Flag controlling whether the program printing trace messages is a CGI program (default is no). This means that trace messages will be printed as HTML. Unless $Logfile is also set, messages will be printed to stdout so they appear in the output page.
t(messages) Print the given strings, if tracing is enabled. Unless $CGI is true or $Logfile is set, each message will be printed to stderr with a newline appended.
trace(messages) Synonym for t(messages).
d(scalar) Return a string representation of a scalar’s value suitable for use in a trace statement. This is just a wrapper for Data::Dumper.

d() will exit with ’’ if trace is not turned on. This is to stop your program being slowed down by generating lots of strings for trace statements that are never printed.

dmp(scalar) Synonym for d(scalar).
check_argv() Looks at the global @ARGV of command-line parameters to find one called ’--trace’. If this is found, it will be removed from @ARGV and tracing will be turned on. Since tracing is off by default, calling check_argv() is a way to make your program print trace only when you ask for it from the command line.


Ed Avis,


perl(1), Data::Dumper(3).


Hey! <B>The above document had some coding errors, which are explained below:B>
Around line 218: You forgot a ’=back’ before ’=head1’
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perl v5.20.3 TRACEMESSAGES (3) 2003-12-05

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