File::Modified - checks intelligently if files have changed


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;
    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, mtime and MD5. The MD5 method will fall back to use timestamps if the Digest::MD5 module cannot be loaded.

There is another module, the File::Signature manpage, 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.

new %ARGS
Creates a new instance. The %ARGS hash has two possible keys, Method, which denotes the method used for checking as default, and Files, which takes an array reference to the filenames to watch.

add filename, method
Adds a new file to watch. method is the method (or rather, the subclass of File::Modified::Signature) to use to determine whether a file has changed or not. The result is either the File::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 File::Modified::Signature subclasses.

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

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


The module also creates a new namespace File::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, as_scalar and from_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 \n or | (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 the Text::Quote manpage as a quoting mechanism to protect against multiline filenames.

Adding new methods for signatures

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


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

* Allow complex structures for the signatures.

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

* Extract the File::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, <>

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


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

 File::Modified - checks intelligently if files have changed