Screen is a full-screen window manager that multiplexes a physical
terminal between several processes, typically interactive shells. Each
virtual terminal provides the functions of the DEC VT100 terminal and,
in addition, several control functions from the ANSI X3.64 (ISO 6429)
and ISO 2022 standards (e.g. insert/delete line and support for multiple
character sets). There is a scrollback history buffer for each virtual
terminal and a copy-and-paste mechanism that allows the user to move
text regions between windows.
When screen is called, it creates a single window with a shell in
it (or the specified command) and then gets out of your way so that you
can use the program as you normally would. Then, at any time, you can
create new (full-screen) windows with other programs in them (including
more shells), kill the current window, view a list of the active
windows, turn output logging on and off, copy text between windows, view
the scrollback history, switch between windows, etc. All windows run
their programs completely independent of each other. Programs continue
to run when their window is currently not visible and even when the
whole screen session is detached from the users terminal.
When a program terminates, screen (per default) kills the window
that contained it. If this window was in the foreground, the display
switches to the previously displayed window; if none are left,
screen exits.
Everything you type is sent to the program running in the current window. The only exception to this is the one keystroke that is used to initiate a command to the window manager. By default, each command begins with a control-a (abbreviated C-a from now on), and is followed by one other keystroke. The command character (see section Command Character) and all the key bindings (see section Key Binding) can be fully customized to be anything you like, though they are always two characters in length.
The standard way to create a new window is to type C-a c. This creates a new window running a shell and switches to that window immediately, regardless of the state of the process running in the current window. Similarly, you can create a new window with a custom command in it by first binding the command to a keystroke (in your `.screenrc' file or at the C-a : command line) and then using it just like the C-a c command. In addition, new windows can be created by running a command like:
screen emacs prog.c
from a shell prompt within a previously created window. This will not
run another copy of screen, but will instead supply the command
name and its arguments to the window manager (specified in the $STY environment
variable) who will use it to create the new window. The above example would
start the emacs editor (editing `prog.c') and switch to its window.
If `/etc/utmp' is writable by screen, an appropriate record
will be written to this file for each window, and removed when the
window is closed. This is useful for working with talk,
script, shutdown, rsend, sccs and other
similar programs that use the utmp file to determine who you are. As
long as screen is active on your terminal, the terminal's own
record is removed from the utmp file. See section Login.