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Steven Haryanto
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File::Write::Rotate - Write to files that archive/rotate themselves


version 0.14


 use File::Write::Rotate;

 my $fwr = File::Write::Rotate->new(
     dir          => '/var/log',    # required
     prefix       => 'myapp',       # required
     #suffix      => '.log',        # default is ''
     size         => 25*1024*1024,  # default is 10MB, unless period is set
     histories    => 12,            # default is 10
     #buffer_size => 100,           # default is none

 # write, will write to /var/log/myapp.log, automatically rotate old log files
 # to myapp.log.1 when myapp.log reaches 25MB. will keep old log files up to
 # myapp.log.12.
 $fwr->write("This is a line\n");
 $fwr->write("This is", " another line\n");

 # compress old log files


This module can be used to write to file, usually for logging, that can rotate itself. File will be opened in append mode. Locking will be done to avoid conflict when there are multiple writers. Rotation can be done by size (after a certain size is reached), by time (daily/monthly/yearly), or both.

I first wrote this module for logging script STDERR output to files (see Tie::Handle::FileWriteRotate).


buffer_size => INT

Get or set buffer size. If set to a value larger than 0, then when a write() failed, instead of dying, the message will be stored in an internal buffer first. When the number of buffer exceeds this size, then write() will die upon failure. Otherwise, every write() will try to flush the buffer.

Can be used for example when a program runs as superuser/root then temporarily drops privilege to a normal user. During this period, logging can fail because the program cannot lock the lock file or write to the logging directory. Before dropping privilege, the program can set buffer_size to some larger-than-zero value to hold the messages emitted during dropping privilege. The next write() as the superuser/root will succeed and flush the buffer to disk (provided there is no other error condition, of course).


$obj = File::Write::Rotate->new(%args)

Create new object. Known arguments:

  • dir => STR (required)

    Directory to put the files in.

  • prefix => STR (required)

    Name of files. The files will be named like the following:


    <period> will only be given if the period argument is set. If period is set to yearly, <period> will be YYYY (4-digit year). If period is monthly, <period> will be YYYY-MM (4-digit year and 2-digit month). If period is daily, <period> will be YYYY-MM-DD (4-digit year, 2-digit month, and 2-digit day).

    <rotate_suffix> is either empty string for current file; or .1, .2 and so on for rotated files. .1 is the most recent rotated file, .2 is the next most recent, and so on.

    An example, with prefix set to myapp:

     myapp         # current file
     myapp.1       # most recently rotated
     myapp.2       # the next most recently rotated

    With prefix set to myapp, period set to monthly, suffix set to .log:

     myapp.2012-12.log     # file name for december 2012
     myapp.2013-01.log     # file name for january 2013

    Like previous, but additionally with size also set (which will also rotate each period file if it exceeds specified size):

     myapp.2012-12.log     # file(s) for december 2012
     myapp.2013-01.log     # file(s) for january 2013

    All times will use local time, so you probably want to set TZ environment variable or equivalent methods to set time zone.

  • suffix => STR (default: '')

    Suffix to give to file names, usually file extension like .log. See prefix for more details.

    If you use a yearly period, setting suffix is advised to avoid ambiguity with rotate suffix (for example, is myapp.2012 the current file for year 2012 or file with 2012 rotate suffix?)

  • size => INT (default: 10*1024*1024)

    Maximum file size, in bytes, before rotation is triggered. The default is 10MB (10*1024*1024) if period is not set. If period is set, no default for size is provided, which means files will not be rotated for size (only for period).

  • period => STR

    Can be set to either daily, monthly, or yearly. If set, will automatically rotate after period change. See prefix for more details.

  • histories => INT (default: 10)

    Number of rotated files to keep. After the number of files exceeds this, the oldest one will be deleted. 0 means not to keep any history, 1 means to only keep .1 file, and so on.

  • buffer_size => INT (default: 0)

    Set initial value of buffer. See the buffer_size attribute for more information.


Write to file. Will automatically rotate file if period changes or file size exceeds specified limit. When rotating, will only keep a specified number of histories and delete the older ones. Uses locking, so multiple writers do not clobber one another. Lock file is named <prefix>.lck. Will wait for up to 1 minute to acquire lock, will die if failed to acquire lock.

Does not append newline so you'll have to do it yourself.


Compress old rotated files. Currently uses pigz or gzip program to do the compression. Extension given to compressed file is .gz.

Normally, should be done using a separate process so as to avoid blocking the writers.

Will not lock writers, but will create <prefix>-compress.pid PID file to prevent multiple compression processes running and to signal the writers to postpone rotation.

After compression is finished, will remove the PID file, so rotation can be done again on the next write() if necessary.


Log::Dispatch::FileRotate, which inspires this module. Differences between File::Write::Rotate (FWR) and Log::Dispatch::FileRotate (LDFR) are as follows:

  • FWR is not part of the Log::Dispatch family.

    This makes FWR more general to use.

    For using together with Log::Dispatch/Log4perl, I have also written Log::Dispatch::FileWriteRotate which is a direct (although not a perfect drop-in) replacement for Log::Dispatch::FileRotate.

  • Secondly, FWR does not use Date::Manip.

    Date::Manip is relatively large (loading Date::Manip 6.37 equals to loading 34 files and ~ 22k lines; while FWR itself is only < 1k lines!)

    As a consequence of this, FWR does not support DatePattern; instead, FWR replaces it with a simple daily/monthly/yearly period.

  • And lastly, FWR supports compressing and rotating compressed old files.

    Using separate processes like the Unix logrotate utility means having to deal with yet another race condition. FWR takes care of that for you (see the compress() method). You also have the option to do log compression in the same script/process if you want, which is convenient.

There is no significant overhead difference between FWR and LDFR (FWR is slightly faster than LDFR on my testing).

Tie::Handle::FileWriteRotate and Log::Dispatch::FileWriteRotate, which use this module.


Why use autorotating log?

Mainly convenience and low maintenance. You no longer need a separate rotator like the Unix logrotate utility (which when accidentally disabled or misconfigured will cause your logs to stop being rotated and grow indefinitely).

What is the downside of using FWR (and LDFR)?

Mainly performance overhead, as every write() involves locking to make it safe to use with multiple processes. Tested on my Core i5 3.1 GHz desktop, writing log lines in the size of ~ 200 bytes, raw writing to disk (SSD) has the speed of around 3.4mil/s, while using FWR it comes down to around 19.5k/s.

However, this is not something you'll notice or need to worry about unless you're logging near that speed.


Steven Haryanto <stevenharyanto@gmail.com>


This software is copyright (c) 2013 by Steven Haryanto.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.