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Log::Log4perl::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!\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, simililarily as with "change_detected()".

SEE ALSO

AUTHOR

     Mike Schilli, <log4perl@perlmeister.com>
 
 

COPYRIGHT AND LICENSE

Copyright 2003 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.