From: John Carter <john.carter@...>
Date: 2005-07-21T10:18:56+09:00
Subject: Re: Hotfolders or "watched" folders in Ruby?

On Thu, 21 Jul 2005, Keith Fahlgren wrote:

> I'd like to have a daemon process that watches for new files in a
> specific directory and then runs a command on them once they're there.

If you are on Linux, it would be trivial to wrap something around 
/dev/inotify

From /usr/src/linux/Documentation/filesystems/inotify.txt
or..
http://www.ibiblio.org/peanut/Kernel-2.6.12/filesystems/inotify.txt

                                     inotify
              a powerful yet simple file change notification system



Document started 15 Mar 2005 by Robert Love <rml@novell.com>

(i) User Interface

Inotify is controlled by a device node, /dev/inotify.  If you do not use 
udev,
this device may need to be created manually.  First step, open it

         int dev_fd = open ("/dev/inotify", O_RDONLY);

Change events are managed by "watches".  A watch is an (object,mask) pair 
where
the object is a file or directory and the mask is a bitmask of one or more
inotify events that the application wishes to receive.  See 
<linux/inotify.h>
for valid events.  A watch is referenced by a watch descriptor, or wd.

Watches are added via a file descriptor.

Watches on a directory will return events on any files inside of the 
directory.

Adding a watch is simple,

         /* 'wd' represents the watch on fd with mask */
         struct inotify_request req = { fd, mask };
         int wd = ioctl (dev_fd, INOTIFY_WATCH, &req);

You can add a large number of files via something like

         for each file to watch {
                 struct inotify_request req;
                 int file_fd;

                 file_fd = open (file, O_RDONLY);
                 if (fd < 0) {
                         perror ("open");
                         break;
                 }

                 req.fd = file_fd;
                 req.mask = mask;

                 wd = ioctl (dev_fd, INOTIFY_WATCH, &req);

                 close (fd);
         }



John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
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Carter's Clarification of Murphy's Law.

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From this principle, all of life and physics may be deduced.