[SOLVED] Getting KVM guest names and writing them to an array

chucklesp9 · 12-14-2011, 09:05 PM

I have looked all over and am unable to find a good answer.

I need to get the names of all KVM guests running and write them to an array so I can validate the names against a database.

Thanks for the help!

David the H. · 12-15-2011, 09:05 AM

What, where, what?

Get the lists of guests from where? What program do you use to get the info you want, and in what format is the output? And put them into what kind of array? What language are we talking about? A shell script? And most important, what have you tried to do so far?

The more details you provide, the greater the chance someone will be able to help you.

And when you do, please remember to use [code][/code] tags around your code and data, to preserve formatting and to improve readability.

chucklesp9 · 12-15-2011, 08:12 PM

I am running Fedora 16 with QEMU-KVM installed running 4 VMs. I have to automate the testing for checking that the names of the VMs match the names given in a MySQL database.

I know that the following will display the running VMs in the terminal:

Code:

virsh list

I then tried using the above command as a function and reading the guest names from it. Here is the code I am using:

Code:

function name()
{ virsh list
}
arr=name
echo ${arr[*]}

I tried this with no success as it only writes the word "name" to the array. I have tried adding a $ before the function name with no success.

I have also tired gathering the names from the following file:
/etc/libvirt/qemu

This is the file where all the .xml config files are stored for each VM. The only problem I have with writing these to an array is that I have exclude anything that does not have VM in the name (eg. VM7.xml).

chucklesp9 · 12-16-2011, 08:27 AM

Sorry I forgot to post the output of the virsh list command and mention that you have to be logged in as root in the terminal.

Code:

[root@linux /]# virsh list
 Id Name                 State
----------------------------------
  1 VM2                  running
  2 VM3                  running
  3 VM6                  running
  4 VM1                  running

David the H. · 12-16-2011, 08:57 AM

Code:

arr=name

This is not the proper syntax for setting an array. All this does is set the simple variable "arr" to the string value "name".

See here for the correct forms for setting and using arrays:

http://mywiki.wooledge.org/BashGuide/Arrays
http://mywiki.wooledge.org/BashFAQ/005

In addition, a function acts as a command, just like any other, which means it only executes if it's the first word in a command string. To use the output of one command inside another, you generally have to use a command or process substitution, or similar nested command form.

http://mywiki.wooledge.org/BashGuide...ands#Functions
http://mywiki.wooledge.org/CommandSubstitution
http://mywiki.wooledge.org/ProcessSubstitution

BTW, function definitions properly use either "function foo", or "foo()", but not "function foo()".

http://mywiki.wooledge.org/BashPitfa...tion_foo.28.29

From the output of your command, you have to do some post-processing in order to extract only the second field. In this case awk is probably the best choice to use. So overall, you'd probably want to do something like this:

Code:

name(){
	virsh list | awk '( $1 ~ /^[0-9]+$/ ) { print $2 }'
}

arr=( $( name ) )
echo "${arr[*]}"

...Or perhaps put the whole thing in the function, with something like this:

Code:

name(){
	mapfile -t arr < <( virsh list | awk '( $1 ~ /^[0-9]$/ ) { print $2 }' )
}

name
echo "${arr[*]}"

Or even just use the command stand-alone, of course.

chucklesp9 · 12-16-2011, 08:20 PM

This worked perfectly. Thanks for the help. I really appreciate it.