I know very little of X11, but running the env command in my terminal, I spotted an environment variable WINDOWID, that shows the same number in different tabs of the same terminal, but a different number in another terminal. Perhaps that's what you need?

It does appear to be an Xterm thing (and probably any terminal that mimicks Xterms behaviour. The xterm(1) man page only says:

ENVIRONMENT

 Xterm sets several environment variables: ... WINDOWID is set to the X window id number of the xterm window. 

Some other possibly relevant questions with answers:

• https://unix.stackexchange.com/questions/3197/how-to-identify-which-xterm-a-shell-or-process-is-running-in

• Get X window id from process in bash

I know very little of X11, but running the env command in my terminal, I spotted an environment variable WINDOWID, that shows the same number in different tabs of the same terminal, but a different number in another terminal. Perhaps that's what you need?

It does appear to be an Xterm thing (and probably any terminal that mimicks Xterms behaviour. The xterm(1) man page only says:

ENVIRONMENT

 Xterm sets several environment variables: ... WINDOWID is set to the X window id number of the xterm window. 

Some other possibly relevant questions with answers:

• https://unix.stackexchange.com/questions/3197/how-to-identify-which-xterm-a-shell-or-process-is-running-in

• Get X window id from process in bash

I know very little of X11, but running the env command in my terminal, I spotted an environment variable WINDOWID, that shows the same number in different tabs of the same terminal, but a different number in another terminal. Perhaps that's what you need?

It does appear to be an Xterm thing (and probably any terminal that mimicks Xterms behaviour. The xterm(1) man page only says:

ENVIRONMENT

 Xterm sets several environment variables: ... WINDOWID is set to the X window id number of the xterm window. 

Some other possibly relevant questions with answers:

• http://unix.stackexchange.com/questions/3197/how-to-identify-which-xterm-a-shell-or-process-is-running-in

• Get X window id from process in bash

I know very little of X11, but running the env command in my terminal, I spotted an environment variable WINDOWID, that shows the same number in different tabs of the same terminal, but a different number in another terminal. Perhaps that's what you need?

It does appear to be an Xterm thing (and probably any terminal that mimicks Xterms behaviour. The xterm(1) man page only says:

ENVIRONMENT

 Xterm sets several environment variables: ... WINDOWID is set to the X window id number of the xterm window. 

Some other possibly relevant questions with answers:

• https://unix.stackexchange.com/questions/3197/how-to-identify-which-xterm-a-shell-or-process-is-running-in

• Get X window id from process in bash