Regular expression matching X session identifiers?

Question

I'm trying to create a utility for extracting the first display that a user is physically at using grep and awk:

$ w | grep -P '^naftuli' | awk '{print $3;}'
:0
reprisal
tmux(2464).%0
tmux(2464).%1
tmux(2464).%2

I have seen variant X session identifiers, is there a standard format that I could implement a regular expression for?

Answer 1

On a modern Unix system, there are two types of X displays: local or (TCP) remote. A local display name is : followed by a number, and optionally but rarely followed by . and a screen number. A remote display is a host name or IP address followed by a local display name. Thus, in ERE syntax:

/([-.0-9A-Za-z]+|\[[0-9A-Fa-f:]\]):[0-9]+(\.[0-9]+)?/

In practice, “it's X if and only if there's a :” should work.