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.\" ========================================================================
.\"
.IX Title "Config::Watch 3pm"
.TH Config::Watch 3pm "2014-03-05" "perl v5.18.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
Log::Log4perl::Config::Watch \- Detect file changes
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    use Log::Log4perl::Config::Watch;
\&
\&    my $watcher = Log::Log4perl::Config::Watch\->new(
\&                          file            => "/data/my.conf",
\&                          check_interval  => 30,
\&                  );
\&
\&    while(1) {
\&        if($watcher\->change_detected()) {
\&            print "Change detected!\en";
\&        }
\&        sleep(1);
\&    }
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module helps detecting changes in files. Although it comes with the
\&\f(CW\*(C`Log::Log4perl\*(C'\fR distribution, it can be used independently.
.PP
The constructor defines the file to be watched and the check interval 
in seconds. Subsequent calls to \f(CW\*(C`change_detected()\*(C'\fR will
.IP "\(bu" 4
return a false value immediately without doing physical file checks
if \f(CW\*(C`check_interval\*(C'\fR hasn't elapsed.
.IP "\(bu" 4
perform a physical test on the specified file if the number
of seconds specified in \f(CW\*(C`check_interval\*(C'\fR 
have elapsed since the last physical check. If the file's modification
date has changed since the last physical check, it will return a true 
value, otherwise a false value is returned.
.PP
Bottom line: \f(CW\*(C`check_interval\*(C'\fR allows you to call the function
\&\f(CW\*(C`change_detected()\*(C'\fR as often as you like, without paying the performing
a significant performance penalty because file system operations 
are being performed (however, you pay the price of not knowing about
file changes until \f(CW\*(C`check_interval\*(C'\fR seconds have elapsed).
.PP
The module clearly distinguishes system time from file system time. 
If your (e.g. \s-1NFS\s0 mounted) file system is off by a constant amount
of time compared to the executing computer's clock, it'll just
work fine.
.PP
To disable the resource-saving delay feature, just set \f(CW\*(C`check_interval\*(C'\fR 
to 0 and \f(CW\*(C`change_detected()\*(C'\fR will run a physical file test on
every call.
.PP
If you already have the current time available, you can pass it
on to \f(CW\*(C`change_detected()\*(C'\fR as an optional parameter, like in
.PP
.Vb 1
\&    change_detected($time)
.Ve
.PP
which then won't trigger a call to \f(CW\*(C`time()\*(C'\fR, but use the value
provided.
.SS "\s-1SIGNAL MODE\s0"
.IX Subsection "SIGNAL MODE"
Instead of polling time and file changes, \f(CW\*(C`new()\*(C'\fR can be instructed 
to set up a signal handler. If you call the constructor like
.PP
.Vb 4
\&    my $watcher = Log::Log4perl::Config::Watch\->new(
\&                          file    => "/data/my.conf",
\&                          signal  => \*(AqHUP\*(Aq
\&                  );
.Ve
.PP
then a signal handler will be installed, setting the object's variable 
\&\f(CW\*(C`$self\->{signal_caught}\*(C'\fR to a true value when the signal arrives.
Comes with all the problems that signal handlers go along with.
.SS "\s-1TRIGGER CHECKS\s0"
.IX Subsection "TRIGGER CHECKS"
To trigger a physical file check on the next call to \f(CW\*(C`change_detected()\*(C'\fR
regardless if \f(CW\*(C`check_interval\*(C'\fR has expired or not, call
.PP
.Vb 1
\&    $watcher\->force_next_check();
.Ve
.PP
on the watcher object.
.SS "\s-1DETECT MOVED FILES\s0"
.IX Subsection "DETECT MOVED FILES"
The watcher can also be used to detect files that have moved. It will 
not only detect if a watched file has disappeared, but also if it has
been replaced by a new file in the meantime.
.PP
.Vb 4
\&    my $watcher = Log::Log4perl::Config::Watch\->new(
\&        file           => "/data/my.conf",
\&        check_interval => 30,
\&    );
\&
\&    while(1) {
\&        if($watcher\->file_has_moved()) {
\&            print "File has moved!\en";
\&        }
\&        sleep(1);
\&    }
.Ve
.PP
The parameters \f(CW\*(C`check_interval\*(C'\fR and \f(CW\*(C`signal\*(C'\fR limit the number of physical 
file system checks, similarily as with \f(CW\*(C`change_detected()\*(C'\fR.
.SH "LICENSE"
.IX Header "LICENSE"
Copyright 2002\-2013 by Mike Schilli <m@perlmeister.com> 
and Kevin Goess <cpan@goess.org>.
.PP
This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.
.SH "AUTHOR"
.IX Header "AUTHOR"
Please contribute patches to the project on Github:
.PP
.Vb 1
\&    http://github.com/mschilli/log4perl
.Ve
.PP
Send bug reports or requests for enhancements to the authors via our
.PP
\&\s-1MAILING LIST \s0(questions, bug reports, suggestions/patches): 
log4perl\-devel@lists.sourceforge.net
.PP
Authors (please contact them via the list above, not directly):
Mike Schilli <m@perlmeister.com>,
Kevin Goess <cpan@goess.org>
.PP
Contributors (in alphabetical order):
Ateeq Altaf, Cory Bennett, Jens Berthold, Jeremy Bopp, Hutton
Davidson, Chris R. Donnelly, Matisse Enzer, Hugh Esco, Anthony
Foiani, James FitzGibbon, Carl Franks, Dennis Gregorovic, Andy
Grundman, Paul Harrington, Alexander Hartmaier  David Hull, 
Robert Jacobson, Jason Kohles, Jeff Macdonald, Markus Peter, 
Brett Rann, Peter Rabbitson, Erik Selberg, Aaron Straup Cope, 
Lars Thegler, David Viner, Mac Yang.