Entering and Exiting Emacs
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The usual way to invoke Emacs is with the shell command emacs. Emacs clears the screen and then displays an initial help message and copyright notice.  On a window system, Emacs opens a window of its own. You can begin typing Emacs commands immediately afterward.

Some operating systems insist on discarding all type-ahead when Emacs starts up; they give Emacs no way to prevent this.  Therefore, it is wise to wait until Emacs clears the screen before typing your first editing command.

If you run Emacs from a shell window under the X Window System, run it in the background with emacs&.  This way, Emacs does not tie up the shell window, so you can use it to run other shell commands while Emacs operates its own X windows.

When Emacs starts up, it makes a buffer named *scratch*. That's the buffer you start out in.  The *scratch* uses Lisp Interaction mode; you can use it to type Lisp expressions and evaluate them, or you can ignore that capability and simply doodle.  (You can specify a different major mode for this buffer by setting the variable initial-major-mode in your init file.  See Init File.)

It is also possible to specify files to be visited, Lisp files to be loaded, and functions to be called, by giving Emacs arguments in the shell command line.  See Command Arguments.  But we don't recommend doing this.  The feature exists mainly for compatibility with other editors.

Many other editors are designed to be started afresh each time you want to edit.  You edit one file and then exit the editor.  The next time you want to edit either another file or the same one, you must run the editor again.  With these editors, it makes sense to use a command line argument to say which file to edit.

But starting a new Emacs each time you want to edit a different file does not make sense.  For one thing, this would be annoyingly slow.  For another, this would fail to take advantage of Emacs's ability to visit more than one file in a single editing session.

The recommended way to use GNU Emacs is to start it only once, just after you log in, and do all your editing in the same Emacs session. Each time you want to edit a different file, you visit it with the existing Emacs, which eventually comes to have many files in it ready for editing.  Usually you do not kill the Emacs until you are about to log out.

Exiting Emacs
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There are two commands for exiting Emacs because there are two kinds of exiting: suspending Emacs and killing Emacs.

Suspending means stopping Emacs temporarily and returning control to its parent process (usually a shell), allowing you to resume editing later in the same Emacs job, with the same files, same kill ring, same undo history, and so on.  This is the usual way to exit.

Killing Emacs means destroying the Emacs job.  You can run Emacs again later, but you will get a fresh Emacs; there is no way to resume the same editing session after it has been killed.

C-z
     Suspend Emacs (suspend-emacs).

C-x C-c
     Kill Emacs (save-buffers-kill-emacs).

To suspend Emacs, type C-z (suspend-emacs).  This takes you back to the shell from which you invoked Emacs.  You can resume Emacs with the shell command %emacs in most common shells.

On systems that do not permit programs to be suspended, C-z runs an inferior shell that communicates directly with the terminal, and Emacs waits until you exit the subshell.  (The way to do that is probably with C-d or exit, but it depends on which shell you use.)  The only way on these systems to get back to the shell from which Emacs was run (to log out, for example) is to kill Emacs.

When Emacs communicates directly with an X server and creates its own dedicated X windows, C-z has a different meaning.  Suspending an applications that uses its own X windows is not meaningful or useful. Instead, C-z runs the command iconify-frame, which temporarily closes up the selected Emacs frame.  The way to get back to a shell window is with the window manager.

To kill Emacs, type C-x C-c (save-buffers-kill-emacs).  A two-character key is used for this to make it harder to type.  Unless a numeric argument is used, this command first offers to save any modified buffers.  If you do not save them all, it asks for reconfirmation with yes before killing Emacs, since any changes not saved will be lost forever.  Also, if any subprocesses are still running, C-x C-c asks for confirmation about them, since killing Emacs will kill the subprocesses immediately.

The operating system usually listens for certain special characters whose meaning is to kill or suspend the program you are running. This operating system feature is turned off while you are in Emacs. The meanings of C-z and C-x C-c as keys in Emacs were inspired by the use of C-z and C-c on several operating systems as the characters for stopping or killing a program, but that is their only relationship with the operating system.  You can customize these keys to run any commands (see Keymaps).