Config::Watch(3)

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!\n";
        }
        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

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

•   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!\n";
        }
        sleep(1);
    }

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

LICENSE
Copyright 2002-2026 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.