File::Modified - checks intelligently if files have changed

  use strict;
  use File::Modified;

  my $d = File::Modified->new(files=>['Import.cfg','Export.cfg']);

  while (1) {
    my (@changes) = $d->changed;

    if (@changes) {
      print "$_ was changed\n" for @changes;
      $d->update();
    };
    sleep 60;
  };

Second example - a script that knows when any of its modules have changed :

  use File::Modified;
  my $files = File::Modified->new(files=>[values %INC, $0]);

  # We want to restart when any module was changed
  exec $0, @ARGV if $files->changed();

The Modified module is intended as a simple method for programs to detect whether configuration files (or modules they rely on) have changed. There are currently two methods of change detection implemented, CWmtime and CWMD5. The CWMD5 method will fall back to use timestamps if the CWDigest::MD5 module cannot be loaded.

There is another module, File::Signature, which has many similar features, so if this module doesn't do what you need, maybe File::Signature does. There also is quite some overlap between the two modules, code wise. Creates a new instance. The CW%ARGS hash has two possible keys, CWMethod, which denotes the method used for checking as default, and CWFiles, which takes an array reference to the filenames to watch.

add filename, method

Adds a new file to watch. CWmethod is the method (or rather, the subclass of CWFile::Modified::Signature) to use to determine whether a file has changed or not. The result is either the CWFile::Modified::Signature subclass or undef if an error occurred.

addfile LIST

Adds a list of files to watch. The method used for watching is the default method as set in the constructor. The result is a list of CWFile::Modified::Signature subclasses.

update

Updates all signatures to the current state. All pending changes are discarded.

changed

Returns a list of the filenames whose files did change since the construction or the last call to CWupdate (whichever last occurred).

The module also creates a new namespace CWFile::Signature, which sometime will evolve into its own module in its own file. A file signature is most likely of little interest to you; the only time you might want to access the signature directly is to store the signature in a file for persistence and easy comparision whether an index database is current with the actual data.

The interface is settled, there are two methods, CWas_scalar and CWfrom_scalar, that you use to freeze and thaw the signatures. The implementation of these methods is very frugal, there are no provisions made against filenames that contain weird characters like CW\n or CW| (the pipe bar), both will be likely to mess up your one-line-per-file database. An interesting method could be to URL-encode all filenames, but I will visit this topic in the next release. Also, complex (that is, non-scalar) signatures are handled rather ungraceful at the moment.

Currently, I'm planning to use Text::Quote as a quoting mechanism to protect against multiline filenames.

Adding a new signature method is as simple as creating a new subclass of CWFile::Signature. See CWFile::Signature::Checksum for a simple example. There is one point of laziness in the implementation of CWFile::Signature, the CWcheck method can only compare strings instead of arbitrary structures (yes, there ARE things that are easier in Python than in Perl). CWFile::Signature::Digest is a wrapper for Gisle Aas' Digest module and allows you to use any module below the CWDigest namespace as a signature, for example CWFile::Signature::MD5 and CWFile::Signature::SHA1.

* Make the simple persistence solution for the signatures better using Text::Quote.

* Allow complex structures for the signatures.

* Document CWFile::Modified::Signature or put it down into another namespace.

* Extract the CWFile::Modified::Signature subclasses out into their own file.

* Create an easy option to watch a whole directory tree.

None by default.

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

Copyright (C) 2002 Max Maischein

Max Maischein, <corion@cpan.org>

Please contact me if you find bugs or otherwise improve the module. More tests are also very welcome !

perl,Digest::MD5,Digest, File::Signature.