Get a build number from a text file

[Phillip Do]

I am a new baby to Jenkins and I could not go all the old posts to look for what I need help !

I have a Jenkins setup and my Jenkins monitors a specific file such as the lastbuildfound.txt in builds folder. This text file contains the last successful build no.

Whenever this text file is updated with a new build number, my Jenkins will trigger by the FSTrigger Plugin . However, Jenkins generates a build number in sequence such as 1, 2, or etc.

The reason I created this setup to run an automation on new build which I don't want to involve with a build person.

The problem is that my Jenkins is not triggering by a source control, so I want to be able to get the build number from a text build and update the build number in Jenkins to match it. 

I know that there is the EnvInject  plugin but I don't know how to use it or any methods.

Please help me to achieve this issue and give me a clear instruction / steps.

Thanks in advance.