This is a fairly straightforward script you've asked about, so this will be an easy explanation.
The most important line in the diskspace script is:
df -k | awk -f $tempfile
Let's just run a quick df -k so you can see the output in question:
$ df -k
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/disk0s9 156277884 63170972 92850912 40% /
devfs 101 101 0 100% /dev
fdesc 1 1 0 100% /dev
<volfs> 512 512 0 100% /.vol
/dev/disk1s3 156159792 138235824 17923968 89% /Volumes/X2
automount -nsl [206] 0 0 0 100% /Network
automount -fstab [214] 0 0 0 100% /automount/Servers
automount -static [214] 0 0 0 100% /automount/static
The important thing to see here is that I have one non-root drive, /Volumes/X2, and that it shows up in the list exactly in that format.
This means that you can weed out other drives by using a call to grep. I'd tally up all drives on /Volume by doing this:
df -k | grep /Volumes | awk -f $tempfile
You could be even more specific, by using your hard disk name too:
df -k | grep /Volumes/Documents\ HD | awk -f $tempfile
Either way, changing that one line should accomplish what you seek.
In terms of automatically emailing the results every 24 hours, that's a job for crontab. Start with man crontab and you'll find that it's not too terribly hard to figure out.
If you would like to learn more about crontab and related administrative features of Unix, I suggest my brand new fourth edition of Teach Yourself Unix in 24 Hours.
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Dave,
While it is certainly possible to alter the script to filter the output for a specific filesystem, isn't it better to leave the script as is and just pipe the output to a filter instead? That output can then be piped to a mailer program to send mail. Finally, the whole command can be scheduled using cron. Here's an example crontab that runs the full command at 12:00 every day.
* 12 * * * diskspace | grep -e 'Filesystem' -e '/Volumnes/Documents HD' | mailx -s '/Volumnes/Documents HD Diskspace' user@host