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Config::Watch(3)      User Contributed Perl Documentation     Config::Watch(3)

       Log::Log4perl::Config::Watch - Detect file changes

	   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!\n";

       This module helps detecting changes in files. Although it comes with
       the "Log::Log4perl" distribution, it can	be used	independently.

       The constructor defines the file	to be watched and the check interval
       in seconds. Subsequent calls to "change_detected()" will

       o   return a false value	immediately without doing physical file	checks
	   if "check_interval" hasn't elapsed.

       o   perform a physical test on the specified file if the	number of
	   seconds specified in	"check_interval" 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.

       Bottom line: "check_interval" allows you	to call	the function
       "change_detected()" 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 "check_interval" seconds have elapsed).

       The module clearly distinguishes	system time from file system time.  If
       your (e.g. NFS mounted) file system is off by a constant	amount of time
       compared	to the executing computer's clock, it'll just work fine.

       To disable the resource-saving delay feature, just set "check_interval"
       to 0 and	"change_detected()" will run a physical	file test on every

       If you already have the current time available, you can pass it on to
       "change_detected()" as an optional parameter, like in


       which then won't	trigger	a call to "time()", but	use the	value

       Instead of polling time and file	changes, "new()" can be	instructed to
       set up a	signal handler.	If you call the	constructor like

	   my $watcher = Log::Log4perl::Config::Watch->new(
				 file	 => "/data/my.conf",
				 signal	 => 'HUP'

       then a signal handler will be installed,	setting	the object's variable
       "$self->{signal_caught}"	to a true value	when the signal	arrives.
       Comes with all the problems that	signal handlers	go along with.

       To trigger a physical file check	on the next call to
       "change_detected()" regardless if "check_interval" has expired or not,


       on the watcher object.

       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.

	   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!\n";

       The parameters "check_interval" and "signal" limit the number of
       physical	file system checks, similarily as with "change_detected()".

       Copyright 2002-2013 by Mike Schilli <> and Kevin Goess

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

       Please contribute patches to the	project	on Github:

       Send bug	reports	or requests for	enhancements to	the authors via	our

       MAILING LIST (questions,	bug reports, suggestions/patches):

       Authors (please contact them via	the list above,	not directly): Mike
       Schilli <>, Kevin Goess	<>

       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.

perl v5.32.0			  2020-07-22		      Config::Watch(3)


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