a program to monitor a directory on Linux

Question

There is a directory where a buddy adds new builds of a product.

The listing looks like this

$ ls path-to-dir/
01
02
03
04
$

where the numbers listed are not files but names of directories containing the builds.

I have to manually go and check every time whether there is a new build or not. I am looking for a way to automate this, so that the program can send an email to some people (including me) whenever path-to-dir/ is updated.

• Do we have an already existing utility or a Perl library that does this?

  inotify.h does something similar, but it is not supported on my kernel (2.6.9).

I think there can be an easy way in Perl.

• Do you think this will work?

  Keep running a loop in Perl that does a ls path-to-dir/ after, say, every 5 minutes and stores the results in an array. If it finds that the new results are different from the old results, it sends out an email using Mail or Email.

Answer 1

Can't it be a simple shell script?

while :;do
        n = 'ls -al path-to-dir | wc -l'
        if n -gt old_n
    # your Mail code here; set old_n=n also
        fi
   sleep 5
done

Answer 2

Checking for different ls output would send a message even when something is deleted or renamed in the directory. You could instead look for files with an mtime newer than the last message sent.

Here's an example in bash, you can run it every 5 minutes:

now=`date +%Y%m%d%H%M.%S`

if [ ! -f "/path/to/cache/file" ] || [ -n "`find /path/to/build/dir -type f -newer /path/to/cache/file`" ]
then
    touch /path/to/cache/file -t "$now"
    sendmail -t <<< "
To: [email protected]
To: [email protected]
Subject: New files found

Dear friend,
I have found a couple of new files.
"
fi

Answer 3

Yes, a loop in Perl as described would do the trick.

You could keep a track of when the directory was last modified; if it hasn't changed, there isn't a new build. If it has changed, an old build might have been deleted or a new one added. You probably don't want to send alerts when old builds are removed; it is crucial that the email is sent when new builds are added.

However, I think that msw has the right idea; the build should notify when it has completed the copy out to the new directory. It should be a script that can be changed to notify the correct list of people - rather than a hard-wired list of names in the makefile or whatever other build control system you use.

Answer 4

If you're going for perl, I'm sure the excellent File::ChangeNotify module will be extremely helpful to you. It can use inotify, if available, but also all sorts of other file-watching mechanisms provided by different platforms. Also, as a fallback, it has its own watching implementation, which works on every platform, but is less efficient than the specialized ones.

Answer 5

you could use dnotify it is the predecessor of inotify and should be available on your kernel. It is still supported by newer kernels.