Shell Programming and Scripting

Hello,
I'm writing a script to monitor different filesystems in multiple servers. And depending on the % free, my script will send an Alert email if % free is less than threshold.
I want to keep a input_feed_file which would have "server,filesystem".
If I run a script a host 'a', then I can find the file systems usage on that server. But I'm intrested to watch few more filesystems that are in host 'b'.

How do I find the disk usage from my script, of these filesystems which aren't on one single server.
I'm not inclined to use any monitoring tools, so I'm trying to accomplish this in one single Korn shell script.
-------------------------------------------
Example of Input file:
host_a,/export/appl/filesystem_a/
host_a,/export/appl/filesystem_b/
host_b,/export/appl/filesystem_y/
.
.
.
--------------------------------------------

Thanks in advance.

short pseudo-code sketch:

Code:

for line in input_file
do
  server=split line ...
  dir = split line ...
  output=`ssh server du -m dir`
  usage=split output ...
  if [ usage > treshold]
  then
    do something
  fi
done

Thanks. I knew it could be done with ssh. But I was wondering if there is any way (any command) to find out disk usage for different filesystems not mounted on the server that you're script is running.

For now I'm getting the file system usage by connecting with ssh, but the downside is, I had to get ssh keys setup on all the hosts for my app id.

use nagios

or

invoke df -H from all server.

Regards,
Bash