File::Modified(3) 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();


This module provides a simple mechanism for identifying when the contents of one or more files have changed. It was initially intended for programs to detect when their configuration files (or the module 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 are a number of other modules on CPAN that provide similar functionality; they are listed in ``SEE ALSO'' below.

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 Text::Quote 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' Digest 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 Text::Quote.

* 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, <[email protected]>

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