NAME

File::Tail - Perl extension for reading from continously updated files

SYNOPSIS

use File::Tail;
$file=File::Tail->new("/some/log/file");
while (defined($line=$file->read)) {
    print "$line";
}

use File::Tail;
$file=File::Tail->new(name=>$name, maxinterval=>300, adjustafter=>7);
while (defined($line=$file->read)) {
    print "$line";
}

Note that the above script will never exit. If there is nothing being written to the file, it will simply block.

DESCRIPTION

The primary purpose of File::Tail is reading and analysing log files while they are being written, which is especialy usefull if you are monitoring the logging process with a tool like Tobias Oetiker's MRTG.

The module tries very hard not to "busy-wait" on a file that has little traffic. Any time it reads new data from the file, it counts the number of new lines, and divides that number by the time that passed since data were last written to the file before that. That is considered the average time before new data will be written. When there is no new data to read, File::Tail sleeps for that number of seconds. Thereafter, the waiting time is recomputed dynamicaly. Note that File::Tail never sleeps for more than the number of seconds set by maxinterval.

Note that the sleep and time used are from Time::HiRes, so this module should do the right thing even if the time to sleep is less than one second.

CONSTRUCTOR

new ([ ARGS ])

Creates a File::Tail. If it has only one paramter, it is assumed to be the filename. If the open fails, or there is some other kind of error, it returns undef, and the error in $!;

You can pass several parameters to new:

name

This is the name of the file to open. The file will be opened for reading. This must be a regular file, not a pipe or a terminal (i.e. it must be seekable).

maxinterval

The maximum number of seconds (real number) that will be spent sleeping. Default is 60, meaning File::Tail will never spend more than sixty seconds without checking the file.

interval

The initial number of seconds (real number) that will be spent sleeping, before the file is first checked. Default is ten seconds, meaning File::Tail will sleep for 10 seconds and then determine, how many new lines have appeared in the file.

adjustafter

The number of times File::Tail waits for the current interval, before adjusting the interval upwards. The default is 10.

resetafter

The number of seconds after last change when File::Tail decides the file may have been closed and reopened. The default is adjustafter*maxinterval.

debug

Set to nonzero if you want to see more about the inner workings of File::Tail. Otherwise not useful.

METHODS

read

read returns one line from the input file. If there are no lines ready, it blocks until there are.

TO BE DONE

This should eventualy work with a tied filehandle. Tests should be devised and put into test.pl.

AUTHOR

Matija Grabnar, matija.grabnar@arnes.si

SEE ALSO

perl(1), tail (1), MRTG

(http://ee-staff.ethz.ch/~oetiker/webtools/mrtg/mrtg.html)