Command for display of Memory usage, Disk Usage and CPU Load

Try this, it works on my Debian system, the details may vary depending on your the implementation of these tools that your OS uses:

#!/bin/sh
free -m | awk 'NR==2{printf "Memory Usage: %s/%sMB (%.2f%)\n", $3,$2,$3*100/$2 }'
df -h | awk '$NF=="/"{printf "Disk Usage: %d/%dGB (%s)\n", $3,$2,$5}'
top -bn1 | grep load | awk '{printf "CPU Load: %.2f\n", $(NF-2)}' 

If you save the above as a script and run it, you will get (example from my system):

$ ./foo.sh 
Memory Usage: 4986/7994MB (62.37%)
Disk Usage: 23/68GB (35%)
CPU Load: 0.78

Note that the script above is giving the disk usage for the / partition. You did not specify what you wanted so I'm guessing that's what you're after.

Check atop.

Read this, https://lwn.net/Articles/387202/

See,

You can see load of disk / memory / cpu by apps:

For example, disk usage:

atop gathered statistics in the directory /var/log/atop/ in binary format files per days. You could read a man page, there must be a way to extract needful information.

There's nothing to display exactly in your particular format, but these provide some of the info, as an alternative it's possible to read valuse from /proc and /sys.

free - quick overview

vmstat 1 shows system performance i/o stats

top dynamic

htop similar to top

I think you need nagios help, for all this plugins/srcipts for nagios are already made and you can download and test without nagios installation.

If you are using solaris, check this out: showcpucount

This will give you an idea of how to go about writing your code.