Log::Any::Adapter::DERIV - standardised logging to STDERR and JSON file


    use Log::Any;

    # print text log to STDERR, json format when inside docker container,
    # colored text format when STDERR is a tty, non-colored text format when
    # STDERR is redirected.
    use Log::Any::Adapter ('DERIV');

    #specify STDERR directly
    use Log::Any::Adapter ('DERIV', stderr => 1)

    #specify STDERR's format
    use Log::Any::Adapter ('DERIV', stderr => 'json')

    #specify the json log name
    use Log::Any::Adapter ('DERIV', json_log_file => '/var/log/program.json.log');


Applies some opinionated log handling rules for Log::Any.

This is extremely invasive. It does the following, affecting global state in various ways:

  • applies UTF-8 encoding to STDERR

  • writes to a .json.log file.

  • overrides the default Log::Any::Proxy formatter to provide data as JSON

  • when stringifying, may replace some problematic objects with simplified versions

An example of the string-replacement approach would be the event loop in asynchronous code: it's likely to have many components attached to it, and dumping that would effectively end up dumping the entire tree of useful objects in the process. This is a planned future extension, not currently implemented.


This is provided as a CPAN module as an example for dealing with multiple outputs and formatting. The existing Log::Any::Adapter modules tend to cover one thing, and it's not immediately obvious how to extend formatting, or send data to multiple logging mechanisms at once.

Although the module may not be directly useful, it is hoped that other teams may find parts of the code useful for their own logging requirements.

There is a public repository on Github, anyone is welcome to fork that and implement their own version or make feature/bug fix suggestions if they seem generally useful:


  • json_log_file

    Specify a file name to which you want the json formatted logs printed into. If not given, then it prints the logs to STDERR.


    If it is true, then print logs to STDERR

    If the value is json or text, then print logs with that format

    If the value is just a true value other than `json` or `text`, then if it is running in a container, then it prints the logs in `json` format. Else if STDERR is a tty, then it prints `colored text` format. Else it prints non-color text format.

If no parameters provided, then default `stderr => 1`;



Applies UTF-8 to filehandle if it is not utf-flavoured already

  • $fh file handle


Formatting the log entry with timestamp, from which the message populated, severity and message.

If color/colour param passed it adds appropriate color code for timestamp, log level, from which this log message populated and actual message. For non-color mode, it just returns the formatted message.

    $object->format_line($data, {color => $color});
  • $data hashref - The data with stack info like package method from which the message populated, timestamp, severity and message

  • $opts hashref - the options color

Returns only formatted string if non-color mode. Otherwise returns formatted string with embedded ANSI color code using Term::ANSIColor


Add format and add color code using format_line and writes the log entry

*$data hashref - The log data


Process the data before printing out. Reduce the continues Future stack messages and filter the messages based on log level.

  • $data hashref - The log data.

Returns a hashref - the processed data


Filter the stack message based on log level.

  • $data hashref - Log stack data

Returns hashref - the filtered data


Go through the caller stack and if continuous Future messages then keep only one at the first.

  • $data hashref - Log stack data

Returns a hashref - the reduced log data


Check the filehandle opened to tty

  • $fh file handle

Returns boolean


Returns true if we think we are currently running in a container.

At the moment this only looks for a .dockerenv file in the root directory; future versions may expand this to provide a more accurate check covering other container systems such as `runc`.

Returns boolean


Based on the type of lock requested, it packs into linux binary flock structure and return the string of that structure.

Linux struct flock: "s s l l i" short l_type short - Possible values: F_RDLCK(0) - read lock, F_WRLCK(1) - write lock, F_UNLCK(2) - unlock short l_whence - starting offset off_t l_start - relative offset off_t l_len - number of consecutive bytes to lock pid_t l_pid - process ID

  • $type integer lock type - F_WRLCK or F_UNLCK

Returns a string of the linux flock structure


call fcntl to lock or unlock a file handle

  • $fh file handle

  • $type lock type, either F_WRLCK or F_UNLCK

Returns boolean or undef


Lock a file handler with fcntl.

  • $fh File handle

Returns boolean


Unlock a file handler locked by fcntl

  • $fh File handle

Returns boolean


Return the current log level name.



alert, critical, debug, emergency, error, info, init, is_alert, is_critical, is_debug, is_emergency, is_error, is_info, is_notice, is_trace, is_warning, notice, trace, warning




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