How to use screen to pair program.

How to use screen to pair program. April 2, 2010

Pair programming is a great way for 2 people to work together on the same code. Typically, it's done with the programmers sitting right next to each other. But what if they are in separate places, or they just don't want to accidentally touch elbows (ewww...)?

The UNIX screen command is typically used to run multiple terminal programs inside a single ssh session, and be able to disconnect/re-connect to the session without the programs noticing. It's an awesome utility, but you can also use it to let multiple people interact with the same terminal screen, and hence, allow multiple people to use the same editor at the same time.

First, I'm assuming both programmers have a user account on the same machine, and are already logged in (or ssh'd in) to the machine. (If the second programmer doesn't have an account, he can use the first programmer's account, and the steps below are the same.)

Enabling multi-user with `screen`

There are two ways to do this. One way is to do

chmod u+s /usr/bin/screen

first, and then make sure everyone's ~/.screenrc file contains:

multiuser on
acladd second_programmer_username

The other way is to just have

multiuser on
acladd root

But then the second programmer will need to do sudo screen instead of just screen in the steps below. (There are also more advanced security options.)

First Programmer: run `screen`

The first programmer starts his day by doing:

screen

Hit ENTER to dismiss the screen startup message. Then, go about your normal activities, such as running vim, or grep, or whatever.

Second Programmer: attach to his screen

The second user does the following:

[sudo] screen -rx first_programmer_username/

This attaches to the other user's active screen.

That's it! Now you should both be seing the same window and can both use their keyboard.

Problems with the Delete Button?

When ssh'ing from a terminal in Mac OSX I noticed that my delete button no longer worked. (ssh'ing from PuTTY in Windows didn't have this problem.) To fix this, do:

TERM=screen; screen

whereever you would normally do screen. Or, it's probably easier to just put

alias screen='TERM=screen; screen'

in your ~/.bashrc file.

Essential commands while inside `screen`


Command Purpose
Ctrl-a ? Show the screen help menu
Ctrl-a d Dettach from the screen (without killing it)
Ctrl-a c Create another window inside the screen.
Ctrl-a <space>   Cycle to the next window.
Ctrl-a a Alternate to the previous window.
Ctrl-a [ Enter "scroll mode" (use Up/Down arrows, then ESC to exit).

Command	Purpose
Ctrl-a ?	Show the `screen` help menu
Ctrl-a d	Dettach from the screen (without killing it)
Ctrl-a c	Create another window inside the screen.
Ctrl-a <space>	Cycle to the next window.
Ctrl-a a	Alternate to the previous window.
Ctrl-a [	Enter "scroll mode" (use Up/Down arrows, then ESC to exit).

Other `screen` flags


Command-line Purpose
screen -ls List all the active screens I have on this machine.
screen Start a new screen session.
screen -x Reattach to my pre-existing screen session.

Command-line	Purpose
screen -ls	List all the active screens I have on this machine.
screen	Start a new screen session.
screen -x	Reattach to my pre-existing screen session.

Enabling multi-user with screen

First Programmer: run screen