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1052 lines
40 KiB
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1052 lines
40 KiB
Plaintext
How is this Emacs different from all other Emacses? -*-Outline-*-
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This file describes the differences between GNU Emacs 19, Twenex
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Emacs, Gosling Emacs (including the commercial versions by Unipress)
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and CCA Emacs.
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* Copyright (c) 1985 Richard M. Stallman
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Permission is granted to anyone to make or distribute verbatim copies
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of this document as received, in any medium, provided that the
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copyright notice and permission notice are preserved,
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and that the distributor grants the recipient permission
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for further redistribution as permitted by this notice.
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Permission is granted to distribute modified versions
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of this document, or of portions of it,
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under the above conditions, provided also that they
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carry prominent notices stating who last changed them.
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Updated March 1993 for Emacs 19 by Eric S. Raymond
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* How is this Emacs different from Twenex Emacs?
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** Fundamental concepts.
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*** There is no concept of "typeout" in GNU Emacs.
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Any time that a command wants to display some output,
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it creates a buffer (usually with a name surrounded by asterisks)
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and displays it in a window.
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This provides some advantages:
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you can edit some more while looking at the output;
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you can copy parts of the output into other buffers.
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It also has a disadvantage that you must type a command
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in order to make the output disappear.
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You can use C-x 1 to get rid of all windows except the
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selected one. To be more selective, you can switch to
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the window you want to get rid of and then type C-x 0
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(delete-window).
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You also need to type a command to scroll the other
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window if not all the output fits in it. Meta-Control-v
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will usually do the job.
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*** There is no concept of a "subsystem" in GNU Emacs.
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Where Twenex Emacs would use a subsystem, GNU Emacs
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instead creates a buffer and redefines commands in it.
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For example, when you send mail in GNU Emacs, you use
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a buffer named *mail* which is in Mail Mode. You can
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switch away from this buffer to any other buffer and
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resume normal editing; then switch back and resume
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composing mail. You do not have to "exit" from
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composing mail in order to do ordinary editing.
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This has many advantages, but it also has a disadvantage:
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Subsystems in Emacs tend to have "exit" commands that return you
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to whatever you were doing before entering the subsystem.
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In GNU Emacs the idea of what to return to is not well defined,
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so it is not clear what an "exit" command should do.
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The only way to "exit" in general is to type C-x b, C-x C-f, or
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some other suitable command to switch buffers. Some
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subsystem-like major modes, such as Info and Mail mode, provide
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commands to "exit" by switching to the previously selected
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buffer.
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*** Files are always visited in their own buffers.
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Beginning users of Twenex Emacs were told how to edit
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using a single buffer and reading one file after another
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into that buffer. Use of a new buffer for each file was
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regarded as a more advanced mode.
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In GNU Emacs, the idea of using a single buffer for various
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files, one by one, has been dropped, given that the address
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space is expected to be large enough for many buffers. C-x
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C-f (find-file), which behaves nearly the same as in Twenex
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Emacs, is in GNU Emacs the canonical way for all users to
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visit files.
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Various commands need to read files into Emacs in the course
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of their execution. In Twenex Emacs the user must tell them
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whether to reuse buffers or create new ones, using the variable
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Tags Find File. In GNU Emacs, these commands always use
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C-x C-f.
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The command C-x C-v does still exist; it kills the current
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buffer and reads the specified file into a new buffer.
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It is equivalent to kill-buffer followed by find-file.
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Since there is no reusing of buffers, there is no point in
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calling the initial buffer "main". So the initial buffer
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in GNU Emacs is called "*scratch*" and is intended for typing
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Lisp expressions to be evaluated.
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*** File name defaulting.
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GNU Emacs records a separate working directory for each buffer.
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Normally this is the directory on which the buffer's file
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resides; for buffers not visiting any file, it is copied from
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the buffer that was current when it was created. The current buffer's
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working directory can be printed with M-x pwd and set with M-x cd.
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GNU Emacs shows you the default directory by inserting it in
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the minibuffer when a file name is being read. You can type
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the filename you want at the end of the default as if the
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default were not there, or you can edit and alter the default.
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If you want file /lose/big when the default /foo/defaultdir/
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has been inserted for you, you need not kill the default; simply
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type at the end of it: /foo/defaultdir//lose/big. Such a file
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name is not ordinarily considered valid, but GNU Emacs
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considers it equivalent to /lose/big.
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Likewise, if you want file quux in your home directory, just add
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~/quux to the end of the supplied text, to get
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/foo/defaultdir/~/quux. GNU Emacs sees "/~" and throws away
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everything before the "~".
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You can refer to environment variables also within file names.
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$ followed by the environment variable name is replaced by the
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variable's value. The variable name should either be followed
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by a nonalphanumeric character (which counts as part of the
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file name) or be surrounded by braces {...} (which do not count
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as part of the file name). Thus, if variable USER has value "rms",
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"x/$USER-foo" is expanded to "x/rms-foo", and "x${USER}foo"
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is expanded to "xrmsfoo". Note that this substitution is not
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performed by the primitive file operation functions of GNU Emacs,
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but rather by the interactive file name reader. It is also
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available as a separate primitive, in the function
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substitute-in-file-name.
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*** Exit commands C-z, C-x C-c and C-x C-z.
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There are two ways to exit GNU Emacs: killing and suspending.
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Killing is like what Control-c does to ordinary Unix programs.
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In GNU Emacs, you type C-x C-c to kill it. (This offers to
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save any modified file buffers before really killing Emacs.)
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Suspending is like what Control-z does to ordinary Unix programs.
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To suspend GNU Emacs, type C-x C-z, or type just C-z.
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Note that C-z suspends ordinary programs instantly, but
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Emacs does not suspend until it reads the C-z.
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Usually it is better to suspend: once a system is smart
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enough to have job control, why ever kill an editor?
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You'll just have to make a new one in a minute.
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This is why the convenient command C-z is provided for
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suspending.
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C-c is used as a prefix key for mode-specific commands and for users'
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own commands. We deliberately do not make C-c ever kill Emacs,
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because it should not be so easy to do something irreversible.
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*** Quitting with C-g.
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If you type C-g while GNU Emacs is waiting for input, it
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is an ordinary command (which is defined to beep). If you
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type C-g while Lisp code is executing, it sets a flag which
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causes a special signal, nearly the same as an error, to
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happen at the next safe place in Lisp execution. This usually
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has the effect of aborting the current command in a safe way.
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Because at times there have been bugs causing GNU Emacs to loop
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without checking the quit flag, a special feature causes
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GNU Emacs to be suspended immediately if you type a second C-g
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while the flag is already set. So you can always get out
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of GNU Emacs. Normally GNU Emacs recognizes and clears the quit flag
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quickly enough to prevent this from happening.
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When you resume GNU Emacs after a suspension caused by multiple C-g, it
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asks two questions before resuming execution:
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Checkpoint?
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Dump core?
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Answer each one with `y' or `n' and a Return.
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`y' to Checkpoint? causes immediate auto-saving of all
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buffers in which auto-saving is enabled.
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`y' to Dump core? causes an illegal instruction to be executed.
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This is to enable a wizard to figure out why GNU Emacs was
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looping without checking for quits. Execution does not continue
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after a core dump. If you answer `n', execution continues.
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With luck, GNU Emacs will ultimately check the quit flag,
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and quit normally. If not, and you type another C-g, it
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is suspended again.
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If GNU Emacs is not really hung, just slow, you may invoke
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the double C-g feature without really meaning to. Then just
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resume and answer `n' to both questions, and you will
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arrive at your former state. Presumably the quit you
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wanted will finish happening soon.
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These questions are not asked if you suspend GNU Emacs with the C-z
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command. Continuing GNU Emacs after a C-z takes you straight back
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into editing.
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*** Undoing with C-x u or C-_
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You can undo many commands--up to 10,000 characters worth.
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Each time you type C-x u or C-_, another command or batch of change
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is undone. Undo information is stored per buffer, and the undo
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command always applies to the current buffer. A numeric argument
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serves as a repeat count.
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Consecutive self-inserting characters are undone in groups of twenty.
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*** Different character set.
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GNU Emacs does not expect anyone ever to have a keyboard in which
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the Control key sets an independent bit which may accompany any
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character. The only control characters that can exist are the
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ASCII control characters.
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There is, as a result, no "control prefix" character.
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*** Control-h is the Help character.
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I'm amazed it took me so long to get this idea. In Twenex Emacs, C-h
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and C-b are equivalent commands, making C-h redundant. C-h is not
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only easy to type, it is mnemonic for "Help". So in GNU Emacs the
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Help character is C-h.
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*** Completion is done by TAB, not ESC.
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ESC in the minibuffer is a Meta prefix, same as at top level.
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*** The string-argument reader is the minibuffer is an editor window.
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In GNU Emacs, the line at the bottom of the screen is the minibuffer.
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Commands that want string arguments always use this line to read them,
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and you can use the ordinary Emacs editing commands to edit the
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input. You can terminate input with Return because Return is defined
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as the exit-minibuffer command when in the minibuffer. If you
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are using a command that needs several arguments, terminate each
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one with Return. You cannot separate arguments with Escape
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the way you would in Twenex Emacs.
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The minibuffer window does not overlay other editor windows;
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it is a nearly ordinary editor window which lacks a mode line
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and is "turned off" when not in use. While it IS in use, you
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can switch windows to and from the minibuffer, kill text in other
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windows and yank in the minibuffer, etc.
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You can even issue a command that uses the minibuffer while in the
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minibuffer. This gets you temporarily into a recursive minibuffer.
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However, this is allowed only if you enable it, since it could be
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confusing for beginners.
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When you exit the minibuffer, the cursor immediately moves back to
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column zero of the minibuffer line, to show you that the exit
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command has been obeyed. The minibuffer contents remain on the screen
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until the end of the command, unless some other text is displayed there.
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A single Control-g exits the minibuffer.
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*** There are no &'s or ^R's or spaces in function names.
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For example, the function which is called ^R Forward Word
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in Twenex Emacs is called forward-word in GNU Emacs.
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*** The extension language is Lisp rather than TECO.
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Libraries must be written in Lisp. Meta-ESC reads a Lisp
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expression, evaluates it, and prints the result. Note that
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Meta-ESC is "disabled" by default, so that beginning users
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do not get into the minibuffer by accident in a confusing way.
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Data types available include integers (which double as characters),
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strings, symbols, lists, vectors, buffers, buffer pointers,
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windows, and process channels.
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For now, to learn about writing Lisp code for GNU Emacs, read some of
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the source code, which is in directory ../lisp. Read the GNU Emacs Lisp
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Reference Manual. Also, all Lisp primitives have self-documentation you can
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read with C-h f.
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*** Enabling the error handler.
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GNU Emacs has a Lisp debugger/stepper/trace package, but normally
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errors do not enter the debugger because that is slow, and unlikely to
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be of interest to most users. Set the variable debug-on-error to t to
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cause errors to invoke the debugger. Set debug-on-quit to cause quit
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signals (caused by C-g) to invoke the debugger.
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** Other changes.
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*** More than two windows are allowed.
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C-x 2 splits the current window into two windows,
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one above the other. Initially they both display
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the same buffer.
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C-x 2 now accepts a numeric argument to specify the number of
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lines to give to the uppermost of the two windows it makes.
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C-x 0 kills the current window, making all others larger.
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C-x 1 kills all windows except the current one.
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C-x O switches to the next window down.
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It rotates from the bottom one to the top one.
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An argument serves as a repeat count; negative arguments
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circulate in the reverse order.
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If the same buffer is displayed in several windows,
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changes made in it are redisplayed in all of them.
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*** Side by side windows are supported.
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The command C-x 3 splits the current window into
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two side-by-side windows.
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C-x } makes the selected window ARG columns wider at the
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expense of the windows at its sides. C-x { makes the selected
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window ARG columns narrower. An argument to C-x 5 specifies
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how many columns to give to the leftmost of the two windows made.
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*** Horizontal scrolling of the lines in a window is implemented.
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C-x < (scroll-left) scrolls all displayed lines left,
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with the numeric argument (default 1) saying how far to scroll.
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When the window is scrolled left, some amount of the beginning
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of each nonempty line is replaced by an "$".
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C-x > scrolls right. If a window has no text hidden at the left
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margin, it cannot be scrolled any farther right than that.
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When nonzero leftwards scrolling is in effect in a window.
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lines are automatically truncated at the window's right margin
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regardless of the value of the variable truncate-lines in the
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buffer being displayed.
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*** Return key does not use up empty lines.
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In Twenex Emacs, the Return command advances over an existing
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empty line in some cases. In GNU Emacs, the Return command always
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makes inserts a newline. Twenex Emacs was designed at a time when
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most display terminals did not have the ability to scroll part
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of the screen, and using existing empty lines made redisplay faster.
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Nowadays, terminals that cannot scroll part of the screen are rare,
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so there is no need to make Return behave in a more complicated manner.
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*** Help m.
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Typing C-h m displays documentation of the current major mode.,
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telling you what special commands and features are available
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and how to use them or get more information on them.
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This is simply the documentation, as a function, of the
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symbol which is the value of major-mode. Each major mode
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function has been given documentation intended for C-h m.
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*** Display-hiding features.
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**** Hiding indented lines
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The command C-x $ with numeric argument N causes lines indented by N
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or more columns to become invisible. All you see is " ..." appended
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to the previous line, in place of any number of consecutive invisible
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lines.
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**** Outline Mode.
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Outline mode is designed for editing outline-structured
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files, such as this one.
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Headings should be lines starting with one or more asterisks.
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Major headings have one asterisk, subheadings two, etc.
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Lines not starting with asterisks are body text.
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You can make the body under a heading, or the subheadings
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under a heading, temporarily invisible, or visible again.
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Invisible lines are attached to the end of the previous line
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so they go with it if you kill it and yank it back.
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Commands:
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Meta-} next-visible-heading move by visible headings
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Meta-{ previous-visible-heading move by visible headings
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Meta-x hide-body make all body text invisible (not headings).
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Meta-x show-all make everything in buffer visible.
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The remaining commands are used when dot is on a heading line.
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They apply to some of the body or subheadings of that heading.
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C-c C-h hide-subtree make text and subheadings invisible.
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C-c C-s show-subtree make text and subheadings visible.
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C-c C-i show-children make direct subheadings visible.
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No effect on body, or subheadings 2 or more levels down.
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With arg N, affects subheadings N levels down.
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M-x hide-entry make immediately following body invisible.
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M-x show-entry make it visible.
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M-x hide-leaves make text under heading and under its subheadings invisible.
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The subheadings remain visible.
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M-x show-branches make all subheadings at all levels visible.
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*** C mode is fancy.
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C mode assumes that you put the initial open-brace of
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a function definition at the beginning of a line.
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If you use the popular indenting style that puts this
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open-brace at the end of a line containing a type declaration,
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YOU WILL LOSE: C mode does not know a function starts there.
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Open-brace at the beginning of a line makes it possible
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for C mode to find function boundaries with total reliability;
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something I consider vital and which cannot be done
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if the other style is used.
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The Tab command indents C code very cleverly.
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I know of only one cases in which Tab does not indent C code nicely:
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Expressions continued over several lines with few parentheses.
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Tab does not know the precedences of C operators, so it does
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not know which lines of the expression should go where.
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Using parentheses to indicate the nesting of operators
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except within a line makes this problem go away.
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The indenting algorithm is entirely written in Lisp.
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Tab with a numeric argument in Twenex Emacs indents
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that many lines. It is different in GNU Emacs: it means
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to shift all the lines of a bracketed expression by the
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same amount as the line being indented. For example, if you have
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if (foo)
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{
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hack ();
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/** Well? */
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}
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and type C-u Tab on the line with the open brace, you get
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if (foo)
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{
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hack ();
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/* Well? */
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}
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from indenting the brace line and then shifting the
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lines within the braces rigidly with the first one.
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Meta-Control-q works as in Lisp mode; it should be
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used with dot just before a bracketed grouping, and
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indents each line INSIDE that grouping using Tab.
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If used instead of C-u Tab in the previous example, it makes
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if (foo)
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{
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hack ();
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/* Well? */
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}
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Meta-Control-h puts mark at the end of the current C function
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and puts dot before it.
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Most other Meta-Control commands intended for Lisp expressions
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work usefully in C mode as well.
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*** Meta-g (fill-region) is different.
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In Twenex Emacs, Meta-g fills the region with no paragraph
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boundaries except for blank and indented lines. In GNU Emacs,
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it divides the region into paragraphs in the same manner as
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Meta-], and fills each paragraph separately. There is also
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the function fill-region-as-paragraph which fills the region
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regarding at as a single paragraph regardless even of blank
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or indented lines.
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*** Indented Text Mode instead of Edit Indented Text.
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Twenex Emacs has a command Edit Indented Text which temporarily
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alters some commands for editing indented paragraphs.
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GNU Emacs has instead a separate major mode, Indented Text Mode,
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which is different from ordinary Text Mode in just the same
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alterations. Specifically, in Indented Text Mode,
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Tab runs the function indent-relative, and auto filling indents
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the newly created lines.
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*** But rectangle commands are implemented.
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C-x r r stores the rectangle described by dot and mark
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into a register; it reads the register name from the keyboard.
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C-x r g, the command to insert the contents of a register,
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can be used to reinsert the rectangle elsewhere.
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Other rectangle commands include
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open-rectangle:
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|
insert a blank rectangle in the position and size
|
|
described by dot and mark, at its corners;
|
|
the existing text is pushed to the right.
|
|
clear-rectangle:
|
|
replace the rectangle described by dot ane mark
|
|
with blanks. The previous text is deleted.
|
|
delete-rectangle:
|
|
delete the text of the specified rectangle,
|
|
moving the text beyond it on each line leftward.
|
|
kill-rectangle
|
|
like delete-rectangle but also stores the text of
|
|
the rectangle in the "rectangle kill buffer".
|
|
More precisely, it stores the text as a list of strings
|
|
(one string for each line) in the variable killed-rectangle.
|
|
yank-rectangle
|
|
inserts the text of the last killed rectangle.
|
|
extract-rectangle and delete-extract-rectangle
|
|
these functions return the text of a rectangle
|
|
as a list of strings. They are for use in writing
|
|
other functions that operate on rectangles.
|
|
|
|
*** Keyboard Macros
|
|
|
|
The C-x ( command for defining a keyboard macro can in GNU Emacs
|
|
be given a numeric argument, which means that the new macro
|
|
starts out not empty but rather as the same as the last
|
|
keyboard macro entered. In addition, that last keyboard
|
|
macro is replayed when the C-x ( is typed. C-x ( with an
|
|
argument is thus equivalent to typing plain C-x ( and then
|
|
retyping the last keyboard macro entered.
|
|
|
|
The command write-kbd-macro and append-kbd-macro can be used to
|
|
save a keyboard macro definition in a file. It is represented as
|
|
a Lisp expression which, when evaluated, will define the keyboard
|
|
macro. write-kbd-macro writes the specified file from scratch,
|
|
whereas append-kbd-macro adds to any existing text in the file.
|
|
Both expect the keyboard macro to be saved to be specified by
|
|
name; this means you must use the command name-last-kbd-macro to
|
|
give the macro a name before you can save it.
|
|
|
|
*** The command to resume a terminated tags-search or tags-query-replace
|
|
|
|
is Meta-comma in GNU Emacs.
|
|
|
|
*** Auto Save is on by default.
|
|
|
|
Auto Save mode is enabled by default in all buffers
|
|
that are visiting files.
|
|
|
|
The file name used for auto saving is made by prepending
|
|
"#" to the file name visited.
|
|
|
|
*** Backup files.
|
|
|
|
Since Unix stupidly fails to have file version numbers,
|
|
GNU Emacs compensates slightly in the customary fashion:
|
|
when a file is modified and saved for the first time in
|
|
a particular GNU Emacs run, the original file is renamed,
|
|
appending "~" to its name. Thus, foo.c becomes foo.c~.
|
|
|
|
Emacs can also put a version number into the name of the backup file,
|
|
as in foo.c.~69~ for version number 69. This is an optional feature
|
|
that the user has to enable.
|
|
|
|
*** Mode Line differences.
|
|
|
|
Each window in GNU Emacs has its own mode line, which always
|
|
displays the status of that window's buffer and nothing else.
|
|
The mode line appears at the bottom of the window. It is
|
|
full of dashes, to emphasize the boundaries between windows,
|
|
and is displayed in inverse video if the terminal supports it.
|
|
The information usually available includes:
|
|
|
|
*** Local Modes feature changed slightly.
|
|
|
|
GNU Emacs supports local mode lists much like those in Twenex Emacs,
|
|
but you can only set variables, not commands. You write
|
|
|
|
Local variables:
|
|
tab-width: 10
|
|
end:
|
|
|
|
in the last page of a file, if you want to make tab-width be ten in a
|
|
file's buffer. The value you specify must be a Lisp object!
|
|
It will be read, but not evaluated. So, to specify a string,
|
|
you MUST use doublequotes. For "false", in variables whose
|
|
meanings are true or false, you MUST write nil .
|
|
|
|
Two variable names are special: "mode" and "eval".
|
|
Mode is used for specifying the major mode (as in Twenex Emacs).
|
|
|
|
mode: text
|
|
|
|
specifies text mode. Eval is used for requesting the evaluation
|
|
of a Lisp expression; its value is ignored. Thus,
|
|
|
|
eval: (set-syntax-table lisp-mode-syntax-table)
|
|
|
|
causes Lisp Mode syntax to be used.
|
|
|
|
|
|
Note that GNU Emacs looks for the string "Local variables:"
|
|
whereas Twenex Emacs looks for "Local modes:". This incompatibility
|
|
id deliberate, so that neither one will see local settings
|
|
intended for the other.
|
|
|
|
*** Lisp code libraries.
|
|
|
|
Libraries of commands, and init files, are written in Lisp.
|
|
libraries conventionally have names ending in .el, while the
|
|
init file is named .emacs and is in your home directory.
|
|
|
|
Use Meta-x load-library to load a library. Most standard libraries
|
|
load automatically if you try to use the commands in them.
|
|
|
|
Meta-x byte-compile-file filename
|
|
compiles the file into byte code which loads and runs faster
|
|
than Lisp source code. The file of byte code is given a name
|
|
made by appending "c" to the end of the input file name.
|
|
|
|
Meta-x byte-recompile-directory directoryname
|
|
compiles all files in the specified directory (globbing not allowed)
|
|
which have been compiled before but have been changed since then.
|
|
|
|
Meta-x load-library automatically checks for a compiled file
|
|
before loading the source file.
|
|
|
|
Libraries once loaded do not retain their identity within GNU
|
|
Emacs. Therefore, you cannot tell just what was loaded from a
|
|
library, and you cannot un-load a library. Normally, libraries
|
|
are written so that loading one has no effect on the editing
|
|
operations that you would have used if you had not loaded the
|
|
library.
|
|
|
|
*** Dired features.
|
|
|
|
You can do dired on partial directories --- any pattern
|
|
the shell can glob. Dired creates a buffer named after
|
|
the directory or pattern, so you can dired several different
|
|
directories. If you repeat dired on the same directory or
|
|
pattern, it just reselects the same buffer. Use Meta-x Revert
|
|
on that buffer to read in the current contents of the directory.
|
|
|
|
*** Directory listing features.
|
|
|
|
C-x C-d now uses the default output format of `ls',
|
|
which gives just file names in multiple columns.
|
|
C-u C-x C-d passes the -l switch to `ls'.
|
|
|
|
Both read a directory spec from the minibuffer. It can
|
|
be any pattern that the shell can glob.
|
|
|
|
*** Compiling other programs.
|
|
|
|
Meta-x compile allows you to run make, or any other compilation
|
|
command, underneath GNU Emacs. Error messages go into a buffer whose
|
|
name is *compilation*. If you get error messages, you can use the
|
|
command C-x ` (that is a backquote) to find the text of the next
|
|
error message.
|
|
|
|
You must specify the command to be run as an argument to M-x compile.
|
|
A default is placed in the minibuffer; you can kill it and start
|
|
fresh, edit it, or just type Return if it is what you want.
|
|
The default is the last compilation command you used; initially,
|
|
it is "make -k".
|
|
|
|
*** Searching multiple files.
|
|
|
|
Meta-x grep searches many files for a regexp by invoking grep
|
|
and reading the output of grep into a buffer. You can then
|
|
move to the text lines that grep found, using the C-x ` command
|
|
just as after M-x compile.
|
|
|
|
*** Running inferior shells.
|
|
|
|
Do Meta-x shell to make an inferior shell together with a buffer
|
|
which serves to hold "terminal" input and output of the shell.
|
|
The shell used is specified by the environment variable ESHELL,
|
|
or by SHELL if ESHELL is not set.
|
|
|
|
Use C-h m whilst in the *shell* buffer to get more detailed info.
|
|
|
|
The inferior shell loads the file .emacs_csh or.emacs_sh
|
|
(or similar using whatever name the shell has) when it starts up.
|
|
|
|
M-! executes a shell command in an inferior shell
|
|
and displays the output from it. With a prefix argument,
|
|
it inserts the output in the current buffer after dot
|
|
and sets the mark after the output. The shell command
|
|
gets /dev/null as its standard input.
|
|
|
|
M-| is like M-! but passes the contents of the region
|
|
as input to the shell command. A prefix argument makes
|
|
the output from the command replace the contents of the region.
|
|
|
|
*** Sending mail.
|
|
|
|
Once you enter Mail Mode using C-x m or C-x 4 m or M-x mail,
|
|
C-c becomes a prefix character for mail-related editing commands.
|
|
C-c C-s is vital; that's how you send the message. C-c C-c sends
|
|
and then switches buffers or kills the current window.
|
|
Use C-h m to get a list of the others.
|
|
|
|
*** Regular expressions.
|
|
|
|
GNU Emacs has regular expression facilities like those of most
|
|
Unix editors, but more powerful:
|
|
|
|
**** -- + --
|
|
|
|
+ specifies repetition of the preceding expression 1 or more
|
|
times. It is in other respect like *, which specifies repetition
|
|
0 or more times.
|
|
|
|
**** -- ? --
|
|
|
|
? is like * but matches at most one repetition of the preceding
|
|
expression.
|
|
|
|
**** -- \| --
|
|
|
|
\| specifies an alternative. Two regular expressions A and B with \| in
|
|
between form an expression that matches anything that either A or B will
|
|
match. Thus, "foo\|bar" matches either "foo" or "bar" but no other
|
|
string.
|
|
|
|
\| applies to the larges possible surrounding expressions. Only a
|
|
surrounding \( ... \) grouping can limit the grouping power of \|.
|
|
|
|
Full backtracking capability exists when multiple \|'s are used.
|
|
|
|
**** -- \( ... \) --
|
|
|
|
\( ... \) are a grouping construct that serves three purposes:
|
|
|
|
1. To enclose a set of \| alternatives for other operations.
|
|
Thus, "\(foo\|bar\)x" matches either "foox" or "barx".
|
|
2. To enclose a complicated expression for * to operate on.
|
|
Thus, "ba\(na\)*" matches "bananana", etc., with any number
|
|
of na's (zero or more).
|
|
3. To mark a matched substring for future reference.
|
|
|
|
Application 3 is not a consequence of the idea of a parenthetical
|
|
grouping; it is a separate feature which happens to be assigned as a
|
|
second meaning to the same \( ... \) construct because there is no
|
|
conflict in practice between the two meanings. Here is an explanation
|
|
of this feature.
|
|
|
|
-- \digit --
|
|
|
|
After the end of a \( ... \) construct, the matcher remembers the
|
|
beginning and end of the text matched by that construct. Then, later on
|
|
in the regular expression, you can use \ followed by a digit to mean,
|
|
``match the same text matched this time by the \( ... \) construct.''
|
|
The first nine \( ... \) constructs that appear in a regular expression
|
|
are assigned numbers 1 through 9 in order of their beginnings. \1
|
|
through \9 can be used to refer to the text matched by the corresponding
|
|
\( ... \) construct.
|
|
|
|
For example, "\(.*\)\1" matches any string that is composed of two
|
|
identical halves. The "\(.*\)" matches the first half, which can be
|
|
anything, but the \1 that follows must match the same exact text.
|
|
|
|
**** -- \` --
|
|
|
|
Matches the empty string, but only if it is at the beginning of the buffer.
|
|
|
|
**** -- \' --
|
|
|
|
Matches the empty string, but only if it is at the end of the buffer.
|
|
|
|
**** -- \b --
|
|
|
|
Matches the empty string, but only if it is at the beginning or end of
|
|
a word. Thus, "\bfoo\b" matches any occurrence of "foo" as a separate word.
|
|
"\bball\(s\|\)\b" matches "ball" or "balls" as a separate word.
|
|
|
|
**** -- \B --
|
|
|
|
Matches the empty string, provided it is NOT at the beginning or end of
|
|
a word.
|
|
|
|
**** -- \< --
|
|
|
|
Matches the empty string, provided it is at the beginning of a word.
|
|
|
|
**** -- \> --
|
|
|
|
Matches the empty string, provided it is at the end of a word.
|
|
|
|
**** -- \w --
|
|
|
|
Matches any word-constituent character. The editor syntax table determines
|
|
which characters these are.
|
|
|
|
**** -- \W --
|
|
|
|
Matches any character that is not a word-constituent.
|
|
|
|
**** -- \s<code> --
|
|
|
|
Matches any character whose syntax is <code>. <code> is a letter that
|
|
represents a syntax code: thus, "w" for word constituent, "-" for
|
|
whitespace, "(" for open-parenthesis, etc. Thus, "\s(" matches any
|
|
character with open-parenthesis syntax.
|
|
|
|
**** -- \S<code> --
|
|
|
|
Matches any character whose syntax is not <code>.
|
|
|
|
* How is this Emacs different from Gosling Emacs?
|
|
|
|
** Advantages of Gosling Emacs:
|
|
|
|
1. The program itself is much smaller.
|
|
GNU Emacs uses about 250k more pure storage.
|
|
As a result, Gosling Emacs can run on machines
|
|
that cannot run GNU Emacs. There is not much difference
|
|
in the amount of impure storage in the two programs.
|
|
|
|
2. In some versions there is support for other forks to
|
|
establish communications channels to Emacs (using sockets?).
|
|
|
|
3. There is a direct interface to dbm (data bases).
|
|
|
|
** Advantages of GNU Emacs:
|
|
|
|
*** True Lisp, not Mocklisp.
|
|
|
|
GNU Emacs's extension language has real symbols, lists
|
|
and vectors. Many extensions are much simpler, and some
|
|
become possible that were nearly impossible in Gosling Emacs.
|
|
Many primitives can have cleaner interfaces, and some features
|
|
need not be put in as special primitives because you can do
|
|
them easily yourself.
|
|
|
|
*** But Mocklisp still works.
|
|
|
|
An automatic conversion package plus a run-time library
|
|
allows you to convert a Mocklisp library into a Lisp library.
|
|
|
|
*** Commands are better crafted.
|
|
|
|
For example, nearly every editing function for which a
|
|
numeric argument would make sense as a repeat count does
|
|
accept a repeat count, and does handle a negative argument
|
|
in the way you would expect.
|
|
|
|
*** The manual is clearer.
|
|
|
|
Everyone tells me it is a very good manual.
|
|
|
|
*** Better on-line documentation.
|
|
|
|
Both functions and variables have documentation strings that
|
|
describe exactly how to use them.
|
|
|
|
*** C mode is smart.
|
|
|
|
It really knows how to indent each line correctly,
|
|
for most popular indentation styles. (Some variables
|
|
control which style is used; popular named styles are also supported.)
|
|
|
|
*** Compatible with PDP-10 Emacs, Multics Emacs and Zmacs.
|
|
|
|
The commands in GNU Emacs are nearly the same as in the
|
|
original Emacs and the other Emacses which imitated it.
|
|
(A few have been changed to fit the Unix environment better.)
|
|
|
|
*** Support for Gosling's Emacs commands.
|
|
|
|
M-x set-gosmacs-bindings rebinds many editing commands for
|
|
compatibility with Gosling's Emacs.
|
|
M-x set-gnu-bindings reverses the change.
|
|
|
|
*** Side-by-side windows.
|
|
|
|
You can split a GNU Emacs window either horizontally or
|
|
vertically.
|
|
|
|
*** Redisplay is faster.
|
|
|
|
GNU Emacs sends about the same stuff to the terminal that
|
|
Gosling's does, but GNU Emacs uses much less CPU time to
|
|
decide what to do.
|
|
|
|
*** Entirely termcap-driven.
|
|
|
|
GNU Emacs has nearly no special code for any terminal type. Various
|
|
new termcap strings make it possible to handle all terminals nearly as
|
|
fast as they could be handled by special-case code.
|
|
|
|
*** Display-hiding features.
|
|
|
|
For example, Outline Mode makes it possible for you to edit
|
|
an outline, making entire sub-branches of the outline visible
|
|
or invisible when you wish.
|
|
|
|
*** You can interrupt with Control-G.
|
|
|
|
Even a looping Lisp program can be stopped this way.
|
|
And even a loop in C code does not stop you from killing
|
|
Emacs and getting back to your shell.
|
|
|
|
*** Per-buffer Undo.
|
|
|
|
You can undo the last several changes, in each buffer
|
|
independently.
|
|
|
|
*** The editor code itself is clean.
|
|
|
|
Many people have remarked on how much they enjoy reading
|
|
the code for GNU Emacs.
|
|
|
|
One other note: The program etc/cvtmail that comes with GNU Emacs can
|
|
be used to convert a mail directory for Gosling Emacs's Rmail into a
|
|
Unix mail file that you could read into GNU Emacs's Rmail.
|
|
|
|
* How is this Emacs different from CCA Emacs?
|
|
|
|
** GNU Emacs Lisp vs CCA Elisp.
|
|
|
|
GNU Emacs Lisp does not have a distinction between Lisp functions
|
|
and Emacs functions, or between Lisp variables and Emacs variables.
|
|
The Lisp and the editor are integrated. A Lisp function defined
|
|
with defun is callable as an editor command if you put an
|
|
interactive calling spec in it; for example,
|
|
(defun forward-character (n)
|
|
(interactive "p")
|
|
(goto-char (+ (point) n)))
|
|
defines a function of one argument that moves point forward by
|
|
a specified number of characters. Programs could call this function,
|
|
as in (forward-character 6), or it could be assigned to a key,
|
|
in which case the "p" says to pass the prefix numeric arg as
|
|
the function's argument. As a result of this feature, you often
|
|
need not have two different functions, one to be called by programs
|
|
and another to read arguments from the user conveniently; the same
|
|
function can do both.
|
|
|
|
CCA Elisp tries to be a subset of Common Lisp and tries to
|
|
have as many Common Lisp functions as possible (though it is still
|
|
only a small fraction of full Common Lisp). GNU Emacs Lisp
|
|
is somewhat similar to Common Lisp just because of my Maclisp
|
|
and Lisp Machine background, but it has several distinct incompatibilities
|
|
in both syntax and semantics. Also, I have not attempted to
|
|
provide many Common Lisp functions that you could write in Lisp,
|
|
or others that provide no new capability in the circumstances.
|
|
|
|
GNU Emacs Lisp does not have packages, readtables, or character objects
|
|
(it uses integers to represent characters).
|
|
|
|
On the other hand, windows, buffers, relocatable markers and processes
|
|
are first class objects in GNU Emacs Lisp. You can get information about them
|
|
and do things to them in a Lispy fashion. Not so in CCA Emacs.
|
|
|
|
In GNU Emacs Lisp, you cannot open a file and read or write characters
|
|
or Lisp objects from it. This feature is painful to support, and
|
|
is not fundamentally necessary in an Emacs, because instead you
|
|
can read the file into a buffer, read or write characters or
|
|
Lisp objects in the buffer, and then write the buffer into the file.
|
|
|
|
On the other hand, GNU Emacs Lisp does allow you to rename, delete, add
|
|
names to, and copy files; also to find out whether a file is a
|
|
directory, whether it is a symbolic link and to what name, whether
|
|
you can read it or write it, find out its directory component,
|
|
expand a relative pathname, find completions of a file name, etc.,
|
|
which you cannot do in CCA Elisp.
|
|
|
|
GNU Emacs Lisp uses dynamic scope exclusively. This enables you to
|
|
bind variables which affect the execution of the editor, such as
|
|
indent-tabs-mode.
|
|
|
|
GNU Emacs Lisp code is normally compiled into byte code. Most of the
|
|
standard editing commands are written in Lisp, and many are
|
|
dumped, pure, in the Emacs that users normally run.
|
|
|
|
GNU Emacs allows you to interrupt a runaway Lisp program with
|
|
Control-g.
|
|
|
|
** GNU Emacs Editing Advantages
|
|
|
|
GNU Emacs is faster for many things, especially insertion of text
|
|
and file I/O.
|
|
|
|
GNU Emacs allows you to undo more than just the last command
|
|
with the undo command (C-x u, or C-_). You can undo quite a ways back.
|
|
Undo information is separate for each buffer; changes in one buffer
|
|
do not affect your ability to undo in another buffer.
|
|
|
|
GNU Emacs commands that want to display some output do so by putting
|
|
it in a buffer and displaying that buffer in a window. This
|
|
technique comes from Gosling Emacs. It has both advantages and
|
|
disadvantages when compared with the technique, copied by CCA Emacs
|
|
from my original Emacs which inherited it from TECO, of having "type
|
|
out" which appears on top of the text in the current window but
|
|
disappears automatically at the next input character.
|
|
|
|
GNU Emacs does not use the concept of "subsystems". Instead, it uses
|
|
highly specialized major modes. For example, dired in GNU Emacs has
|
|
the same commands as dired does in other versions of Emacs, give or
|
|
take a few, but it is a major mode, not a subsystem. The advantage
|
|
of this is that you do not have to "exit" from dired and lose the
|
|
state of dired in order to edit files again. You can simply switch
|
|
to another buffer, and switch back to the dired buffer later. You
|
|
can also have several dired buffers, looking at different directories.
|
|
|
|
It is still possible to write a subsystem--your own command loop--
|
|
in GNU Emacs, but it is not recommended, since writing a major mode
|
|
for a special buffer is better.
|
|
|
|
Recursive edits are also rarely used, for the same reason: it is better
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to make a new buffer and put it in a special major mode. Sending
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mail is done this way.
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GNU Emacs expects everyone to use find-file (C-x C-f) for reading
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in files; its C-x C-v command kills the current buffer and then finds
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the specified file.
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As a result, users do not need to think about the complexities
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of subsystems, recursive edits, and various ways to read in files
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or what to do if a buffer contains changes to some other file.
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GNU Emacs uses its own format of tag table, made by the "etags"
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program. This format makes finding a tag much faster.
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Dissociated Press is supported.
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** GNU Emacs Editing Disadvantages.
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GNU Emacs does not display the location of the mark.
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GNU Emacs does not have a concept of numbers of buffers,
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|
or a permanent ordering of buffers, or searching through multiple
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|
buffers. The tags-search command provides a way to search
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|
through several buffers automatically.
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|
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GNU Emacs does not provide commands to visit files without
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|
setting the buffer's default directory. Users can write such
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|
commands in Lisp by copying the code of the standard file
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|
visiting commands and modifying them.
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|
|
|
GNU Emacs does not support "plus options" in the command
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|
arguments or in buffer-selection commands, except for line numbers.
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|
|
|
GNU Emacs does not support encryption. Down with security!
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|
|
|
GNU Emacs does not support replaying keystroke files,
|
|
and does not normally write keystroke files.
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|
|
|
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|
** Neutral Differences
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|
|
|
GNU Emacs uses TAB, not ESC, to complete file names, buffer names,
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|
command names, etc.
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|
|
|
GNU Emacs uses LFD to terminate searches, instead of
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|
the C-d uses by CCA Emacs. (Actually, this character is controlled
|
|
by a parameter in GNU Emacs.) C-M-s in GNU Emacs is an interactive
|
|
regular expression search, but you can get to a noninteractive
|
|
one by typing ESC right after the C-M-s.
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|
|
|
In GNU Emacs, C-x s asks, for each modified file buffer, whether
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|
to save it.
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|
|
|
GNU Emacs indicates line continuation with "\" and line
|
|
truncation (at either margin) with "$".
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|
|
|
The command to resume a tags-search or tags-query-replace in
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|
GNU Emacs is Meta-Comma.
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arch-tag: e5a3da2f-f13d-400e-95e2-b6e1a520af90
|