From: Peter Hickman <peterhickman386@...>
Date: 2012-09-02T17:31:19+09:00
Subject: Re: Ruby module to get df -h output

Depends on your need

Here is the out put from 'df -h' on my system'

Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/disk0s2   465Gi  385Gi   80Gi    83%    /
devfs          191Ki  191Ki    0Bi   100%    /dev
map -hosts       0Bi    0Bi    0Bi   100%    /net
map auto_home    0Bi    0Bi    0Bi   100%    /home
/dev/disk2s2   1.4Ti  489Gi  908Gi    36%    /Volumes/Backup
/dev/disk1s6   466Gi  317Gi  148Gi    69%    /Volumes/Spare

Now insert a new drive and do it again

Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/disk0s2   465Gi  385Gi   80Gi    83%    /
devfs          195Ki  195Ki    0Bi   100%    /dev
map -hosts       0Bi    0Bi    0Bi   100%    /net
map auto_home    0Bi    0Bi    0Bi   100%    /home
/dev/disk2s2   1.4Ti  489Gi  908Gi    36%    /Volumes/Backup
/dev/disk1s6   466Gi  317Gi  148Gi    69%    /Volumes/Spare
/dev/disk3s1    56Mi   37Mi   19Mi    66%    /Volumes/Untitled

Note the new filesystem => /dev/disk3s1

ruby-1.8.7-p302 > File.exists?("/dev/disk3s1")
 => true
ruby-1.8.7-p302 >

Now I remove the disk and we go back to how it was

Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/disk0s2   465Gi  385Gi   80Gi    83%    /
devfs          193Ki  193Ki    0Bi   100%    /dev
map -hosts       0Bi    0Bi    0Bi   100%    /net
map auto_home    0Bi    0Bi    0Bi   100%    /home
/dev/disk2s2   1.4Ti  489Gi  908Gi    36%    /Volumes/Backup
/dev/disk1s6   466Gi  317Gi  148Gi    69%    /Volumes/Spare

See that /dev/disk3s1 is no longer there

ruby-1.8.7-p302 > File.exists?("/dev/disk3s1")
 => false
ruby-1.8.7-p302 >

So as far as my system is concerned /dev/disk3s1 only exists when it
is mounted. This may be sufficient for the task that the OP had. Now I
will concede that it might not work how you might expect for other
devices. File.exists?("/dev/disk0s1") which is not in the df -h list
does return true as it is part of /dev/disk0s2. But the the OP didn't
want to know if "/var/www/html" was mounted (or that the mount point
existed) just that "/dev/cciss/c0d1p1" was mounted, the example that
the OP gives would be true if "/dev/cciss/c0d1p1" was mounted to *any*
mount point not just "/var/www/html".

As I've said File.exists?() might be a sufficient solution for the OP.