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How do I customize a script from "Wicked Cool Shell Scripts"?

Regarding script #41 (calculating available disk space), out of your book Wicked Cool Shell Scripts, I am unclear how I can have this script calculate the free space on one specific drive, namely /Volumes/Documents HD in my case.

I'd also love to know how I can automatically email the results of this same script, say every 24 hours. If you could kindly point me in the right direction, I'm sure I could figure out the rest!

Dave's Answer:

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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Comments

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

Posted by: Howard Hong at October 30, 2009 3:28 PM

I have something to say, now that you mention it, but ...

I do have a lot to say, and questions of my own for that matter, but first I'd like to say thank you for all your efforts on this Web site by buying you a cup of coffee!

I do have a comment, now that you mention it!