Watch a folder and send files by e-mail

My printer is able to convert faxes to PDF documents and save these documents on a network folder.
From there I could do many things. But I need to watch for new documents in a folder.

But first let's setup the Windows / Samba network folder.

Shared folder with Samba

The comment is shown in the file explorer. browseable tells if the folder is listed, and writeable is useful to write and (more interestingly in this case) delete files.
valid users can contain users or groups (prefixed with @) that have the permission to read and (if applicable) write to the folder.
create mask is required because the folder is meant to be shared to a group instead of belonging to a single user. Use 0750 if you only want the creator of the file to be able to remove the file.

I created a sambausers group on my machine and put the appropriate users in it.. Remember you need a system account for each user, and that you need to configure each account through smbpasswd. By the way you can configure Samba with a database or LDAP if you like.

You need to make a new directory and let the sambausers group own it and have read / write / execute (chmod g+rwx) on it. The execute permission on the folder is needed so you can create files in the folder.

Restart Samba. Check you can access the folder from your file manager with the appropriate credentials.

Watch directories on your file system

One great way to do this is the incron daemon. It lets you setup cron-like tasks to execute a shell script or any executable program whenever a change is detected in the folder.

Install incron on your system.

Login with a user with permissions to read files from the shared folder on your Linux box. You can sudo -i -u theUser.

Open man incrontab in one terminal window.

In another window, fire up incrontab -e to edit the tasks associated with the user.

I have mine configured with /srv/shr/IncomingFax IN_CREATE /home/myuser/somescript.sh

You can watch for other events, just read the manual you just opened!

Now everytime a file is created in the IncomingFax folder the script will be executed.

E-mail the file just added

Here is an example of the shell script that I use. It might not be the smartest way to do what it does (particularly because the information of the file added is lost in the process because of how incron works)

The script holds its "state" by using a ".lastfile" because it might happen that the script is executed several times with the same document. I don't know why it does that, I think it's an issue with the printer. You might not need to do that.

Also I happen to have a log file to log what happens with the script. You might not want that either. What you might like though is to verify the extension of the file. Note that the filesystem is case-sensitive so ".PDF" files won't be matched.

Make sure you have mutt installed. It's a bit complicated to send attachments. Sendmail is not enough. Note you can attach several files at once. The argument to the echo command is the message body, and what comes after "-s" is the message subject.

I purposedly let this example in French as a reminder that it is safer to avoid any other encoding than pure ASCII. There has to be a way to cope with UTF-8 but I didn't have time to investigate that issue.

This script has (at least) one limitation. I should actually rewrite it to make it more robust. I am assuming it takes less than 5 seconds for the printer to transfer the file. After 5 seconds I send the file by e-mail. There would be ways to know if the transfer is finished:

• Use a program to read the file. That program probably knows if it's valid.
• Wait until the file size has been constant for some time. Then we can assume the transfer is finished.
• If there are a lot of transfers, we can assume the before-last file was completely transferred when we detect a new file.

There you go. We can now look at a folder, filter files by extension, and send the new file by e-mail.