Synopsis

use Logfile::Tail ();
my $file = new Logfile::Tail('/var/log/messages');
while (<$file>) {
        # process the line
}

and later in different process

my $file = new Logfile::Tail('/var/log/messages');

and continue reading where we've left out the last time. Also possible is to explicitly save the current position:

my $file = new Logfile::Tail('/var/log/messages',
        { autocommit => 0 });
my $line = $file->getline();
$file->commit();

Description

Log files are files that are generated by various running programs. They are generally only appended to. When parsing information from log files, it is important to only read each record / line once, both for performance and for accounting and statistics reasons.

The Logfile::Tail provides an easy way to achieve the read-just-once processing of log files.

The module remembers for each file the position where it left out the last time, in external status file, and upon next invocation it seeks to the remembered position. It also stores checksum of 512 bytes before that position, and if the checksum does not match the file content the next time it is read, it will try to find the rotated file and read the end of it before advancing to newer rotated file or to the current log file.

Both .num and -date suffixed rotated files are supported.

Methods

new()

new( FILENAME [,MODE [,PERMS]], [ { attributes } ] )

new( FILENAME, IOLAYERS, [ { attributes } ] )

Constructor, creates new Logfile::Tail object. Like IO::File, it passes any parameters to method open; it actually creates an IO::File handle internally.

Returns new object, or undef upon error.

open( FILENAME [,MODE [,PERMS]], [ { attributes } ] )

open( FILENAME, IOLAYERS, [ { attributes } ] )

Opens the file using IO::File. If the file was read before, the offset where the reading left out the last time is read from an external file in the ./.logfile-tail-status directory and seek is made to that offset, to continue reading at the last remembered position.

If however checksum, which is also stored with the offset, does not match the current content of the file (512 bytes before the offset are checked), the module assumes that the file was rotated / reused / truncated in the mean time since the last read. It will try to find the checksum among the rotated files. If no match is found, it will reset the offset to zero and start from the beginning of the file.

Returns true, or undef upon error.

The attributes are passed as an optional hashref of key => value pairs. The supported attribute is

autocommit

Value 0 means that no saving takes place; you need to save explicitly using the commit() method.

Value 1 (the default) means that position is saved when the object is closed via explicit close() call, or when it is destroyed. The value is also saved upon the first open.

Value 2 causes the position to be save in all cases as value 1, plus after each successful read.

status_dir

The attribute specifies the directory (or subdirectory of current directory) which is used to hold status files. By default, ./.logfile-tail-status directory is used. To store the status files in the current directory, pass empty string or dot (.).

status_file

The attribute specifies the name of the status file which is used to hold the offset and SHA256 checksum of 512 bytes before the offset. By default, SHA256 of the full (absolute) logfile filename is used as the status file name.

commit()

Explicitly save the current position and checksum in the status file.

Returns true, or undef upon error.

close()

Closes the internal filehandle. It stores the current position and checksum in an external file in the ./.logfile-tail-status directory.

Returns true, or undef upon error.

getline()

Line <$fh> in scalar context.

getlines()

Line <$fh> in list context.

Author and license

Copyright (c) 2010 Jan Pazdziora.

Logfile::Tail is free software. You can redistribute it and/or modify it under the terms of either:

a) the GNU General Public License, version 2 or 3;

b) the Artistic License, either the original or version 2.0.