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

    This document describes version 0.321 of File::Write::Rotate (from Perl
    distribution File-Write-Rotate), released on 2019-06-27.

     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");

    To compressing old log files:


    This is usually done in a separate process, because it potentially takes
    a long time if the files to compress are large; we are rotating
    automatically in write() so doing automatic compression too would
    annoyingly block writer for a potentially long time.

    This module can be used to write to file, usually for logging, that can
    rotate itself. File will be opened in append mode. By default, 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

  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 (a regular Perl array). When the number of items
    in the 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).

  path => str (ro)
    Current file's path.

  handle => (ro)
    Current file handle. You should not use this directly, but use write()
    instead. This attribute is provided for special circumstances (e.g. in
    hooks, see example in the hook section).

  hook_before_write => code
    Will be called by write() before actually writing to filehandle (but
    after locking is done). Code will be passed ($self, \@msgs, $fh) where
    @msgs is an array of strings to be written (the contents of buffer, if
    any, plus arguments passed to write()) and $fh is the filehandle.

  hook_before_rotate => code
    Will be called by the rotating routine before actually doing rotating.
    Code will be passed ($self).

    This can be used to write a footer to the end of each file, e.g.:

     # hook_before_rotate
     my ($self) = @_;
     my $fh = $self->handle;
     print $fh "Some footer\n";

    Since this hook is indirectly called by write(), locking is already

  hook_after_rotate => code
    Will be called by the rotating routine after the rotating process. Code
    will be passed ($self, \@renamed, \@deleted) where @renamed is array of
    new filenames that have been renamed, @deleted is array of new filenames
    that have been deleted.

  hook_after_create => code
    Will be called by after a new file is created. Code will be passed

    This hook can be used to write a header to each file, e.g.:

     # hook_after_create
     my ($self) = @_;
     my $fh $self->handle;
     print $fh "header\n";

    Since this is called indirectly by write(), locking is also already

  binmode => str
    If set to "1", will cause the file handle to be set:

     binmode $fh;

    which might be necessary on some OS, e.g. Windows when writing binary
    data. Otherwise, other defined values will cause the file handle to be

     binmode $fh, $value

    which can be used to set PerlIO layer(s).

  $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

    *   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.

    *   lock_mode => STR (default: 'write')

        Can be set to either "none", "write", or "exclusive". "none"
        disables locking and increases write performance, but should only be
        used when there is only one writer. "write" acquires and holds the
        lock for each write. "exclusive" acquires the lock at object
        creation and holds it until the the object is destroyed.

        Lock file is named "<prefix>"".lck". Will wait for up to 1 minute to
        acquire lock, will die if failed to acquire lock.

    *   hook_before_write => CODE

    *   hook_before_rotate => CODE

    *   hook_after_rotate => CODE

    *   hook_after_create => CODE

        See "ATTRIBUTES".

    *   buffer_size => int

    *   rotate_probability => float (between 0 < x < 1)

        If set, instruct to only check for rotation under a certain
        probability, for example if value is set to 0.1 then will only check
        for rotation 10% of the time.

  lock_file_path => STR
    Returns a string representing the complete pathname to the lock file,
    based on "dir" and "prefix" attributes.

    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.

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

    Compress old rotated files and remove the uncompressed originals.
    Currently uses IO::Compress::Gzip to do the compression. Extension given
    to compressed file is ".gz".

    Will not lock writers, but will create "<prefix>""" 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.

  Why use autorotating file?
    Mainly convenience and low maintenance. You no longer need a separate
    rotator process 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 (significant) performance overhead. At (almost) every "write()",
    FWR needs to check file sizes and/or dates for rotation. Under default
    configuration (where "lock_mode" is "write"), it also performs locking
    on each "write()" to make it safe to use with multiple processes. Below
    is a casual benchmark to give a sense of the overhead, tested on my Core
    i5-2400 3.1GHz desktop:

    Writing lines in the size of ~ 200 bytes, raw writing to disk (SSD) has
    the speed of around 3.4mil/s, while using FWR it goes down to around
    ~13k/s. Using "lock_mode" "none" or "exclusive", the speed is ~52k/s.

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

    If you need more speed, you can try setting "rotate_probability" which
    will cause FWR to only check for rotation probabilistically, e.g. if you
    set this to 0.1 then checks will only be done in about 1 of 10 writes.
    This can significantly reduce the overhead and increase write speed
    several times (e.g. 5-8 times), but understand that this will make the
    writes "overflow" a bit, e.g. file sizes will exceed for a bit if you do
    size-based rotation. More suitable if you only do size-based rotation
    since it is usually okay to exceed sizes for a bit.

  I want a filehandle instead of a File::Write::Rotate object!
    Use Tie::Handle::FileWriteRotate.

    Please visit the project's homepage at

    Source repository is at

    Please report any bugs or feature requests on the bugtracker website

    When submitting a bug or request, please include a test-file or a patch
    to an existing test-file that illustrates the bug or desired feature.

    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

        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

        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 file 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.

    perlancar <>

    This software is copyright (c) 2019, 2016, 2015, 2014, 2013, 2012 by

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