Config::Watch(3pm) User Contributed Perl Documentation Config::Watch(3pm)
NAME
Log::Log4perl::Config::Watch - Detect file changes
SYNOPSIS
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!
";
}
sleep(1);
}
DESCRIPTION
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
call.
If you already have the current time available, you can pass it on to "change_detected()" as an optional parameter, like in
change_detected($time)
which then won't trigger a call to "time()", but use the value provided.
SIGNAL MODE
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.
TRIGGER CHECKS
To trigger a physical file check on the next call to "change_detected()" regardless if "check_interval" has expired or not, call
$watcher->force_next_check();
on the watcher object.
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.
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!
";
}
sleep(1);
}
The parameters "check_interval" and "signal" limit the number of physical file system checks, simililarily as with "change_detected()".
COPYRIGHT AND LICENSE
Copyright 2002-2009 by Mike Schilli <m@perlmeister.com> and Kevin Goess <cpan@goess.org>.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
perl v5.10.1 2010-07-21 Config::Watch(3pm)