––thursday #1: screen

I’m trying something new: every Thursday I’ll go over how to do something with the command line. Let me know what you think.

If you are using a modern-ish browser, you probably use tabs to keep multiple things open at once: your email, your calendar, whatever you’re actually doing, etc. You can do the same thing with the shell using screen: in a single terminal, you can compile a program while you’re editing a file and watching another process out of the corner of your eye.

Note that screen is super handy when SSH’d into a box. SSH in once, then start screen and open up all of the windows you need.

Using screen

To start up screen, run:

$ screen

Now your shell will clear and screen will give you a welcome message.

Screen version 4.00.03jw4 (FAU) 2-May-06
Copyright (c) 1993-2002 Juergen Weigert, Michael Schroeder
Copyright (c) 1987 Oliver Laumann
                          [Press Space or Return to end.]

As it says at the bottom, just hit Return to clear the welcome message. Now you’ll see an empty prompt and you can start working normally.

Let’s say we have three things we want to do:

  1. Run top
  2. Edit a file
  3. Tail a log

Go ahead and start up top:

$ top

Well, now we need to edit a file but top‘s using the shell. What to do now? Just create a new window. While top is still running, hit ^A c (I’m using ^A as shorthand for Control-a, so this means “hit Control-a, then hit c”) to create a new window. The new window gets put right on top of the old one, so you’ll see a fresh shell and be at the prompt again. But where did top go? Not to worry, it’s still there. We can switch back to it with ^A n or ^A p (next or previous window).

Now we can start up our editor and begin editing a file. But now we want to tail a file, so we create another new window with ^A c and run our tail -f filename. We can continue to use ^A n and ^A p to switch between the three things we’re doing (and open more windows as necessary).


screen seems pretty ubiquitous, it has been on every Linux machine I’ve ever tried running it on and even OS X (although it may be part of XCode, I haven’t checked).

Note for Emacs Users

^A is an annoying escape key, as it is also go-to-beginning-of-line shortcut in Emacs (and the shell). To fix this, create a .screenrc file and add one line to change this to something else:

# use ^T
escape ^Tt
# or ^Y
escape ^Yy

The escape sequence is 3 characters: carat, T, and t. (It is not using the single special character “^T”.) The traditional escape key is actually Ctrl-^, as the carat is the one character Emacs doesn’t use for anything. In a .screenrc file, this results in the rather bizarre string:

escape ^^^^

…which makes sense when you think about it, but looks a bit weird.

Odds and Ends

As long as you’re poking at the .screenrc file, you might want to turn off the welcome message, too:

startup_message off

Run ^A ? anytime for help, or check out the manual’s list of default bindings.

Did I miss anything? Get anything wrong? Got a suggestion for next week? Leave a comment below and let me know!

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