Appending specific clipboard string to a text file

Greetings,

I have a script that copies mutilline text to clipboard. The clipboard text has be assigned a variable, can be seen in a messagebox, and is shown below.

DeviceName:       Test1

Version:                1.2

DeviceSerial:       123456789

Last Line:             Text End

I am trying to get the "123456789" string and append it to a text file. I've expiremented with StringRegExpReplace, but have not had too much luck. Could someone please point me in the right direction? An example would be fanatatic.

Thanks in advance!