Provided by: libfile-write-rotate-perl_0.29-1_all 
NAME
File::Write::Rotate - Write to files that archive/rotate themselves
VERSION
This document describes version 0.29 of File::Write::Rotate (from Perl distribution File-
Write-Rotate), released on 2015-10-20.
SYNOPSIS
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:
$fwr->compress;
This is usually done in a separate process, because it potentially takes a long time if
the files to compress are large; we are rotating automatically in write() so doing
automatic compression too would annoyingly block writer for a potentially long time.
DESCRIPTION
This module can be used to write to file, usually for logging, that can rotate itself.
File will be opened in append mode. By default, locking will be done to avoid conflict
when there are multiple writers. Rotation can be done by size (after a certain size is
reached), by time (daily/monthly/yearly), or both.
I first wrote this module for logging script STDERR output to files (see
Tie::Handle::FileWriteRotate).
ATTRIBUTES
buffer_size => int
Get or set buffer size. If set to a value larger than 0, then when a write() failed,
instead of dying, the message will be stored in an internal buffer first (a regular Perl
array). When the number of items in the buffer exceeds this size, then write() will die
upon failure. Otherwise, every write() will try to flush the buffer.
Can be used for example when a program runs as superuser/root then temporarily drops
privilege to a normal user. During this period, logging can fail because the program
cannot lock the lock file or write to the logging directory. Before dropping privilege,
the program can set buffer_size to some larger-than-zero value to hold the messages
emitted during dropping privilege. The next write() as the superuser/root will succeed and
flush the buffer to disk (provided there is no other error condition, of course).
path => str (ro)
Current file's path.
handle => (ro)
Current file handle. You should not use this directly, but use write() instead. This
attribute is provided for special circumstances (e.g. in hooks, see example in the hook
section).
hook_before_write => code
Will be called by write() before actually writing to filehandle (but after locking is
done). Code will be passed ($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 $fh "Some footer\n";
Since this hook is indirectly called by write(), locking is already done.
hook_after_rotate => code
Will be called by the rotating routine after the rotating process. Code will be passed
($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 ($self).
This hook can be used to write a header to each file, e.g.:
# hook_after_create
my ($self) = @_;
my $fh $self->handle;
print $fh "header\n";
Since this is called indirectly by write(), locking is also already done.
binmode => str
METHODS
$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:
<prefix><period><suffix><rotate_suffix>
"<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.2012-12.log.1
myapp.2012-12.log.2
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.
• 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.
$fwr->write(@args)
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.
$fwr->compress
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>""-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.
FAQ
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.
SEE ALSO
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 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.
HOMEPAGE
Please visit the project's homepage at <https://metacpan.org/release/File-Write-Rotate>.
SOURCE
Source repository is at <https://github.com/perlancar/perl-File-Write-Rotate>.
BUGS
Please report any bugs or feature requests on the bugtracker website
<https://rt.cpan.org/Public/Dist/Display.html?Name=File-Write-Rotate>
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.
AUTHOR
perlancar <perlancar@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2015 by perlancar@cpan.org.
This is free software; you can redistribute it and/or modify it under the same terms as
the Perl 5 programming language system itself.