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Jason Moore > CGI-Log > CGI::Log



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Module Version: 1.00   Source  


CGI::Log - Perl extension for centralized logging of debug, error, status and success messages from scripts or other modules.


  use CGI::Log;

  Log->debug("user: $user");            ## add messages
  Log->status("Welcome $user.");
  Log->error("I'm sorry $user, but you do not have access to that area.");

  @msg = Log->get_debug();              ## get messages
  @msg = Log->get_error();
  @msg = Log->get_error("UI");
  @msg = Log->get_status();

  Log->is_error;                        ## test for messages

  Log->debug_off;               ## causes print() and debug() to be skipped

  Log->print();                 ## outputs debug and error logs in HTML
  Log->clear;                   ## clear all entries (current pid)

  Log->_report;                 ## reports the sizes of the arrays (lengths)
  Log->ui_no_error();           ## turns off inclusion of $! in user error messages


This module acts as a central repository for debug, status and error messages. It instantiates itself automatically (if it needs to) so you can access the Log object functions from anywhere in you code including other modules/objects with a simple consistent syntax.

It was written for CGI and mod_perl programming, but it could easily be used in any perl script where there is a need for centralized logging. (The only function which is CGI specific is print() since it outputs the debug and error logs with HTML formatting.)

It was originally written to just hold debugging information, but it has been extended to hold information that you might want to return to the user (i.e. the user-interface).

It is designed to be very painless to use. Add the following to any script or module where you want to log messages:

        use CGI::Log;

The CGI::Log:: namespace has been aliased to Log:: in order to save a bit of typing when adding debugging messages. So, to add a debug message, enter:

        Log->debug("Your message here.");
        ## note: this is equivalent to CGI::Log->debug();

To add an error message:

        Log->error("Some information about the error goes here.");

To add an success, or status message:

        Log->status("A status or informational message for the user.");
        Log->success("Something worked properly.");

The following commands all retrieve the messages you've logged:

        @msg = Log->get_debug;
        @msg = Log->get_error;
        @msg = Log->get_error("UI");
        @msg = Log->get_status;
        @msg = Log->get_success;

Note: All the get_* methods return array references when called in scalar context. e.g.

        $msg = Log->get_success;        ## ref($msg) eq "ARRAY"

During CGI/mod_perl development it is very handy to dump all of the debugging messages at the bottom of the HTML page. This is done with:


This can just be left at the bottom of your main script. Logging can be turned off (default is on), and when it is turned off Log->print() doesn't do anything.

Types and Formats of Messages

Each of the four types of messages (debug, error, status, success) have slightly different logic. The differences are as follows:

The debug messages are not designed to be visable by the user (and in fact may be a security risk if you show the connection string for databases, etc.) The format of a debug message is:

        [caller:line [caller:line...]] message


        caller is a method name
        line is the line number from the method 
        message is your debugging message 

An example will make this clearer:


    1:      use CGI::Log;
    2:      &foo;
    3:      sub foo
    4:      {
    5:            Log->debug("We are on line 5 of the method: foo");
    6:            &bar;
    7:      }
    8:      sub bar
    9:      {
    10:           Log->debug("line 10 method: bar process id: " . $$);
    11:           Log->error("Error on line 11 in the method: bar");
    12:     }
    13:     Log->print();

When run it prints:

    -- DEBUG ( (pid: 3262) --
    [main:2 main::foo:5] We are on line 5 of the method: foo
    [main:2 main::foo:6 main::bar:10] line 10 method: bar process id: 456
    [ERROR] [main:2 main::foo:6 main::bar:11] This an error being called from the method: bar (No such file or directory)
    -- ERROR --
    [main:2 main::foo:6 main::bar:11] Error on line 11 in the method: bar (No such file or directory)

(Note: the HTML in the output has been removed for clarity.)

There are some things to note:

Log messages of type "status" and "success" are not manipulated or modified. Whatever you put in is what you get back.

Log messages of type "error" are stored in two formats. The first is the format that in the output above. The second is suitable for returning to the user. (It doesn't include the call trace.) By default it includes the error message from the variable $!. If this is not desirable, call Log->ui_no_error()


Documentation for CGI::Log was created by h2xs.


- too much noise in the debug call tracing under mod_perl. e.g.

        [main:0 (eval):0 Apache::Registry::handler:141 (eval):141 Apache::ROOT::perl::test_5flog_2epl::handler:16] debug message.

- not thread-safe.

- if you are using mod_perl and you do not remember to clean out the log with Log->clean(), you will waste lots of memory.

- CGI::Log takes the Log:: namespace by default. This might be seen as rude, or cause problems if it is already being used. (Check if %Log:: is defined???)


Jason Moore, 1998 <>




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