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1 How is this Emacs different from all other Emacses? -*-Outline-*-
3 This file describes the differences between GNU Emacs 19, Twenex
4 Emacs, Gosling Emacs (including the commercial versions by Unipress)
5 and CCA Emacs.
7 * Copyright (c) 1985 Richard M. Stallman
9 Permission is granted to anyone to make or distribute verbatim copies
10 of this document as received, in any medium, provided that the
11 copyright notice and permission notice are preserved,
12 and that the distributor grants the recipient permission
13 for further redistribution as permitted by this notice.
15 Permission is granted to distribute modified versions
16 of this document, or of portions of it,
17 under the above conditions, provided also that they
18 carry prominent notices stating who last changed them.
20 Updated March 1993 for Emacs 19 by Eric S. Raymond
23 * How is this Emacs different from Twenex Emacs?
25 ** Fundamental concepts.
27 *** There is no concept of "typeout" in GNU Emacs.
29 Any time that a command wants to display some output,
30 it creates a buffer (usually with a name surrounded by asterisks)
31 and displays it in a window.
33 This provides some advantages:
34 you can edit some more while looking at the output;
35 you can copy parts of the output into other buffers.
37 It also has a disadvantage that you must type a command
38 in order to make the output disappear.
39 You can use C-x 1 to get rid of all windows except the
40 selected one. To be more selective, you can switch to
41 the window you want to get rid of and then type C-x 0
42 (delete-window).
44 You also need to type a command to scroll the other
45 window if not all the output fits in it. Meta-Control-v
46 will usually do the job.
48 *** There is no concept of a "subsystem" in GNU Emacs.
50 Where Twenex Emacs would use a subsystem, GNU Emacs
51 instead creates a buffer and redefines commands in it.
53 For example, when you send mail in GNU Emacs, you use
54 a buffer named *mail* which is in Mail Mode. You can
55 switch away from this buffer to any other buffer and
56 resume normal editing; then switch back and resume
57 composing mail. You do not have to "exit" from
58 composing mail in order to do ordinary editing.
60 This has many advantages, but it also has a disadvantage:
61 Subsystems in Emacs tend to have "exit" commands that return you
62 to whatever you were doing before entering the subsystem.
63 In GNU Emacs the idea of what to return to is not well defined,
64 so it is not clear what an "exit" command should do.
65 The only way to "exit" in general is to type C-x b, C-x C-f, or
66 some other suitable command to switch buffers. Some
67 subsystem-like major modes, such as Info and Mail mode, provide
68 commands to "exit" by switching to the previously selected
69 buffer.
71 *** Files are always visited in their own buffers.
73 Beginning users of Twenex Emacs were told how to edit
74 using a single buffer and reading one file after another
75 into that buffer. Use of a new buffer for each file was
76 regarded as a more advanced mode.
78 In GNU Emacs, the idea of using a single buffer for various
79 files, one by one, has been dropped, given that the address
80 space is expected to be large enough for many buffers. C-x
81 C-f (find-file), which behaves nearly the same as in Twenex
82 Emacs, is in GNU Emacs the canonical way for all users to
83 visit files.
85 Various commands need to read files into Emacs in the course
86 of their execution. In Twenex Emacs the user must tell them
87 whether to reuse buffers or create new ones, using the variable
88 Tags Find File. In GNU Emacs, these commands always use
89 C-x C-f.
91 The command C-x C-v does still exist; it kills the current
92 buffer and reads the specified file into a new buffer.
93 It is equivalent to kill-buffer followed by find-file.
95 Since there is no reusing of buffers, there is no point in
96 calling the initial buffer "main". So the initial buffer
97 in GNU Emacs is called "*scratch*" and is intended for typing
98 Lisp expressions to be evaluated.
100 *** File name defaulting.
102 GNU Emacs records a separate working directory for each buffer.
103 Normally this is the directory on which the buffer's file
104 resides; for buffers not visiting any file, it is copied from
105 the buffer that was current when it was created. The current buffer's
106 working directory can be printed with M-x pwd and set with M-x cd.
108 GNU Emacs shows you the default directory by inserting it in
109 the minibuffer when a file name is being read. You can type
110 the filename you want at the end of the default as if the
111 default were not there, or you can edit and alter the default.
113 If you want file /lose/big when the default /foo/defaultdir/
114 has been inserted for you, you need not kill the default; simply
115 type at the end of it: /foo/defaultdir//lose/big. Such a file
116 name is not ordinarily considered valid, but GNU Emacs
117 considers it equivalent to /lose/big.
119 Likewise, if you want file quux in your home directory, just add
120 ~/quux to the end of the supplied text, to get
121 /foo/defaultdir/~/quux. GNU Emacs sees "/~" and throws away
122 everything before the "~".
124 You can refer to environment variables also within file names.
125 $ followed by the environment variable name is replaced by the
126 variable's value. The variable name should either be followed
127 by a nonalphanumeric character (which counts as part of the
128 file name) or be surrounded by braces {...} (which do not count
129 as part of the file name). Thus, if variable USER has value "rms",
130 "x/$USER-foo" is expanded to "x/rms-foo", and "x${USER}foo"
131 is expanded to "xrmsfoo". Note that this substitution is not
132 performed by the primitive file operation functions of GNU Emacs,
133 but rather by the interactive file name reader. It is also
134 available as a separate primitive, in the function
135 substitute-in-file-name.
137 *** Exit commands C-z, C-x C-c and C-x C-z.
139 There are two ways to exit GNU Emacs: killing and suspending.
140 Killing is like what Control-c does to ordinary Unix programs.
141 In GNU Emacs, you type C-x C-c to kill it. (This offers to
142 save any modified file buffers before really killing Emacs.)
143 Suspending is like what Control-z does to ordinary Unix programs.
144 To suspend GNU Emacs, type C-x C-z, or type just C-z.
145 Note that C-z suspends ordinary programs instantly, but
146 Emacs does not suspend until it reads the C-z.
148 Usually it is better to suspend: once a system is smart
149 enough to have job control, why ever kill an editor?
150 You'll just have to make a new one in a minute.
151 This is why the convenient command C-z is provided for
152 suspending.
154 C-c is used as a prefix key for mode-specific commands and for users'
155 own commands. We deliberately do not make C-c ever kill Emacs,
156 because it should not be so easy to do something irreversible.
158 *** Quitting with C-g.
160 If you type C-g while GNU Emacs is waiting for input, it
161 is an ordinary command (which is defined to beep). If you
162 type C-g while Lisp code is executing, it sets a flag which
163 causes a special signal, nearly the same as an error, to
164 happen at the next safe place in Lisp execution. This usually
165 has the effect of aborting the current command in a safe way.
167 Because at times there have been bugs causing GNU Emacs to loop
168 without checking the quit flag, a special feature causes
169 GNU Emacs to be suspended immediately if you type a second C-g
170 while the flag is already set. So you can always get out
171 of GNU Emacs. Normally GNU Emacs recognizes and clears the quit flag
172 quickly enough to prevent this from happening.
174 When you resume GNU Emacs after a suspension caused by multiple C-g, it
175 asks two questions before resuming execution:
176 Checkpoint?
177 Dump core?
178 Answer each one with `y' or `n' and a Return.
179 `y' to Checkpoint? causes immediate auto-saving of all
180 buffers in which auto-saving is enabled.
181 `y' to Dump core? causes an illegal instruction to be executed.
182 This is to enable a wizard to figure out why GNU Emacs was
183 looping without checking for quits. Execution does not continue
184 after a core dump. If you answer `n', execution continues.
185 With luck, GNU Emacs will ultimately check the quit flag,
186 and quit normally. If not, and you type another C-g, it
187 is suspended again.
189 If GNU Emacs is not really hung, just slow, you may invoke
190 the double C-g feature without really meaning to. Then just
191 resume and answer `n' to both questions, and you will
192 arrive at your former state. Presumably the quit you
193 wanted will finish happening soon.
195 These questions are not asked if you suspend GNU Emacs with the C-z
196 command. Continuing GNU Emacs after a C-z takes you straight back
197 into editing.
199 *** Undoing with C-x u or C-_
201 You can undo many commands--up to 10,000 characters worth.
202 Each time you type C-x u or C-_, another command or batch of change
203 is undone. Undo information is stored per buffer, and the undo
204 command always applies to the current buffer. A numeric argument
205 serves as a repeat count.
207 Consecutive self-inserting characters are undone in groups of twenty.
209 *** Different character set.
211 GNU Emacs does not expect anyone ever to have a keyboard in which
212 the Control key sets an independent bit which may accompany any
213 character. The only control characters that can exist are the
214 ASCII control characters.
216 There is, as a result, no "control prefix" character.
218 *** Control-h is the Help character.
220 I'm amazed it took me so long to get this idea. In Twenex Emacs, C-h
221 and C-b are equivalent commands, making C-h redundant. C-h is not
222 only easy to type, it is mnemonic for "Help". So in GNU Emacs the
223 Help character is C-h.
225 *** Completion is done by TAB, not ESC.
227 ESC in the minibuffer is a Meta prefix, same as at top level.
229 *** The string-argument reader is the minibuffer is an editor window.
231 In GNU Emacs, the line at the bottom of the screen is the minibuffer.
232 Commands that want string arguments always use this line to read them,
233 and you can use the ordinary Emacs editing commands to edit the
234 input. You can terminate input with Return because Return is defined
235 as the exit-minibuffer command when in the minibuffer. If you
236 are using a command that needs several arguments, terminate each
237 one with Return. You cannot separate arguments with Escape
238 the way you would in Twenex Emacs.
240 The minibuffer window does not overlay other editor windows;
241 it is a nearly ordinary editor window which lacks a mode line
242 and is "turned off" when not in use. While it IS in use, you
243 can switch windows to and from the minibuffer, kill text in other
244 windows and yank in the minibuffer, etc.
246 You can even issue a command that uses the minibuffer while in the
247 minibuffer. This gets you temporarily into a recursive minibuffer.
248 However, this is allowed only if you enable it, since it could be
249 confusing for beginners.
251 When you exit the minibuffer, the cursor immediately moves back to
252 column zero of the minibuffer line, to show you that the exit
253 command has been obeyed. The minibuffer contents remain on the screen
254 until the end of the command, unless some other text is displayed there.
256 A single Control-g exits the minibuffer.
258 *** There are no &'s or ^R's or spaces in function names.
260 For example, the function which is called ^R Forward Word
261 in Twenex Emacs is called forward-word in GNU Emacs.
263 *** The extension language is Lisp rather than TECO.
265 Libraries must be written in Lisp. Meta-ESC reads a Lisp
266 expression, evaluates it, and prints the result. Note that
267 Meta-ESC is "disabled" by default, so that beginning users
268 do not get into the minibuffer by accident in a confusing way.
270 Data types available include integers (which double as characters),
271 strings, symbols, lists, vectors, buffers, buffer pointers,
272 windows, and process channels.
274 For now, to learn about writing Lisp code for GNU Emacs, read some of
275 the source code, which is in directory ../lisp. Read the GNU Emacs Lisp
276 Reference Manual. Also, all Lisp primitives have self-documentation you can
277 read with C-h f.
279 *** Enabling the error handler.
281 GNU Emacs has a Lisp debugger/stepper/trace package, but normally
282 errors do not enter the debugger because that is slow, and unlikely to
283 be of interest to most users. Set the variable debug-on-error to t to
284 cause errors to invoke the debugger. Set debug-on-quit to cause quit
285 signals (caused by C-g) to invoke the debugger.
287 ** Other changes.
289 *** More than two windows are allowed.
291 C-x 2 splits the current window into two windows,
292 one above the other. Initially they both display
293 the same buffer.
295 C-x 2 now accepts a numeric argument to specify the number of
296 lines to give to the uppermost of the two windows it makes.
298 C-x 0 kills the current window, making all others larger.
299 C-x 1 kills all windows except the current one.
300 C-x O switches to the next window down.
301 It rotates from the bottom one to the top one.
302 An argument serves as a repeat count; negative arguments
303 circulate in the reverse order.
305 If the same buffer is displayed in several windows,
306 changes made in it are redisplayed in all of them.
308 *** Side by side windows are supported.
310 The command C-x 3 splits the current window into
311 two side-by-side windows.
313 C-x } makes the selected window ARG columns wider at the
314 expense of the windows at its sides. C-x { makes the selected
315 window ARG columns narrower. An argument to C-x 5 specifies
316 how many columns to give to the leftmost of the two windows made.
318 *** Horizontal scrolling of the lines in a window is implemented.
320 C-x < (scroll-left) scrolls all displayed lines left,
321 with the numeric argument (default 1) saying how far to scroll.
322 When the window is scrolled left, some amount of the beginning
323 of each nonempty line is replaced by an "$".
324 C-x > scrolls right. If a window has no text hidden at the left
325 margin, it cannot be scrolled any farther right than that.
326 When nonzero leftwards scrolling is in effect in a window.
327 lines are automatically truncated at the window's right margin
328 regardless of the value of the variable truncate-lines in the
329 buffer being displayed.
331 *** Return key does not use up empty lines.
333 In Twenex Emacs, the Return command advances over an existing
334 empty line in some cases. In GNU Emacs, the Return command always
335 makes inserts a newline. Twenex Emacs was designed at a time when
336 most display terminals did not have the ability to scroll part
337 of the screen, and using existing empty lines made redisplay faster.
338 Nowadays, terminals that cannot scroll part of the screen are rare,
339 so there is no need to make Return behave in a more complicated manner.
341 *** Help m.
343 Typing C-h m displays documentation of the current major mode.,
344 telling you what special commands and features are available
345 and how to use them or get more information on them.
347 This is simply the documentation, as a function, of the
348 symbol which is the value of major-mode. Each major mode
349 function has been given documentation intended for C-h m.
351 *** Display-hiding features.
353 **** Hiding indented lines
355 The command C-x $ with numeric argument N causes lines indented by N
356 or more columns to become invisible. All you see is " ..." appended
357 to the previous line, in place of any number of consecutive invisible
358 lines.
360 **** Outline Mode.
362 Outline mode is designed for editing outline-structured
363 files, such as this one.
365 Headings should be lines starting with one or more asterisks.
366 Major headings have one asterisk, subheadings two, etc.
367 Lines not starting with asterisks are body text.
369 You can make the body under a heading, or the subheadings
370 under a heading, temporarily invisible, or visible again.
371 Invisible lines are attached to the end of the previous line
372 so they go with it if you kill it and yank it back.
374 Commands:
375 Meta-} next-visible-heading move by visible headings
376 Meta-{ previous-visible-heading move by visible headings
378 Meta-x hide-body make all body text invisible (not headings).
379 Meta-x show-all make everything in buffer visible.
381 The remaining commands are used when dot is on a heading line.
382 They apply to some of the body or subheadings of that heading.
383 C-c C-h hide-subtree make text and subheadings invisible.
384 C-c C-s show-subtree make text and subheadings visible.
385 C-c C-i show-children make direct subheadings visible.
386 No effect on body, or subheadings 2 or more levels down.
387 With arg N, affects subheadings N levels down.
388 M-x hide-entry make immediately following body invisible.
389 M-x show-entry make it visible.
390 M-x hide-leaves make text under heading and under its subheadings invisible.
391 The subheadings remain visible.
392 M-x show-branches make all subheadings at all levels visible.
394 *** C mode is fancy.
396 C mode assumes that you put the initial open-brace of
397 a function definition at the beginning of a line.
398 If you use the popular indenting style that puts this
399 open-brace at the end of a line containing a type declaration,
400 YOU WILL LOSE: C mode does not know a function starts there.
402 Open-brace at the beginning of a line makes it possible
403 for C mode to find function boundaries with total reliability;
404 something I consider vital and which cannot be done
405 if the other style is used.
407 The Tab command indents C code very cleverly.
408 I know of only one cases in which Tab does not indent C code nicely:
409 Expressions continued over several lines with few parentheses.
410 Tab does not know the precedences of C operators, so it does
411 not know which lines of the expression should go where.
412 Using parentheses to indicate the nesting of operators
413 except within a line makes this problem go away.
415 The indenting algorithm is entirely written in Lisp.
417 Tab with a numeric argument in Twenex Emacs indents
418 that many lines. It is different in GNU Emacs: it means
419 to shift all the lines of a bracketed expression by the
420 same amount as the line being indented. For example, if you have
421 if (foo)
422 {
423 hack ();
424 /** Well? */
425 }
426 and type C-u Tab on the line with the open brace, you get
427 if (foo)
428 {
429 hack ();
430 /* Well? */
431 }
432 from indenting the brace line and then shifting the
433 lines within the braces rigidly with the first one.
435 Meta-Control-q works as in Lisp mode; it should be
436 used with dot just before a bracketed grouping, and
437 indents each line INSIDE that grouping using Tab.
438 If used instead of C-u Tab in the previous example, it makes
439 if (foo)
440 {
441 hack ();
442 /* Well? */
443 }
445 Meta-Control-h puts mark at the end of the current C function
446 and puts dot before it.
448 Most other Meta-Control commands intended for Lisp expressions
449 work usefully in C mode as well.
451 *** Meta-g (fill-region) is different.
453 In Twenex Emacs, Meta-g fills the region with no paragraph
454 boundaries except for blank and indented lines. In GNU Emacs,
455 it divides the region into paragraphs in the same manner as
456 Meta-], and fills each paragraph separately. There is also
457 the function fill-region-as-paragraph which fills the region
458 regarding at as a single paragraph regardless even of blank
459 or indented lines.
461 *** Indented Text Mode instead of Edit Indented Text.
463 Twenex Emacs has a command Edit Indented Text which temporarily
464 alters some commands for editing indented paragraphs.
465 GNU Emacs has instead a separate major mode, Indented Text Mode,
466 which is different from ordinary Text Mode in just the same
467 alterations. Specifically, in Indented Text Mode,
468 Tab runs the function indent-relative, and auto filling indents
469 the newly created lines.
471 *** But rectangle commands are implemented.
473 C-x r r stores the rectangle described by dot and mark
474 into a register; it reads the register name from the keyboard.
475 C-x r g, the command to insert the contents of a register,
476 can be used to reinsert the rectangle elsewhere.
478 Other rectangle commands include
479 open-rectangle:
480 insert a blank rectangle in the position and size
481 described by dot and mark, at its corners;
482 the existing text is pushed to the right.
483 clear-rectangle:
484 replace the rectangle described by dot ane mark
485 with blanks. The previous text is deleted.
486 delete-rectangle:
487 delete the text of the specified rectangle,
488 moving the text beyond it on each line leftward.
489 kill-rectangle
490 like delete-rectangle but also stores the text of
491 the rectangle in the "rectangle kill buffer".
492 More precisely, it stores the text as a list of strings
493 (one string for each line) in the variable killed-rectangle.
494 yank-rectangle
495 inserts the text of the last killed rectangle.
496 extract-rectangle and delete-extract-rectangle
497 these functions return the text of a rectangle
498 as a list of strings. They are for use in writing
499 other functions that operate on rectangles.
501 *** Keyboard Macros
503 The C-x ( command for defining a keyboard macro can in GNU Emacs
504 be given a numeric argument, which means that the new macro
505 starts out not empty but rather as the same as the last
506 keyboard macro entered. In addition, that last keyboard
507 macro is replayed when the C-x ( is typed. C-x ( with an
508 argument is thus equivalent to typing plain C-x ( and then
509 retyping the last keyboard macro entered.
511 The command write-kbd-macro and append-kbd-macro can be used to
512 save a keyboard macro definition in a file. It is represented as
513 a Lisp expression which, when evaluated, will define the keyboard
514 macro. write-kbd-macro writes the specified file from scratch,
515 whereas append-kbd-macro adds to any existing text in the file.
516 Both expect the keyboard macro to be saved to be specified by
517 name; this means you must use the command name-last-kbd-macro to
518 give the macro a name before you can save it.
520 *** The command to resume a terminated tags-search or tags-query-replace
522 is Meta-comma in GNU Emacs.
524 *** Auto Save is on by default.
526 Auto Save mode is enabled by default in all buffers
527 that are visiting files.
529 The file name used for auto saving is made by prepending
530 "#" to the file name visited.
532 *** Backup files.
534 Since Unix stupidly fails to have file version numbers,
535 GNU Emacs compensates slightly in the customary fashion:
536 when a file is modified and saved for the first time in
537 a particular GNU Emacs run, the original file is renamed,
538 appending "~" to its name. Thus, foo.c becomes foo.c~.
540 Emacs can also put a version number into the name of the backup file,
541 as in foo.c.~69~ for version number 69. This is an optional feature
542 that the user has to enable.
544 *** Mode Line differences.
546 Each window in GNU Emacs has its own mode line, which always
547 displays the status of that window's buffer and nothing else.
548 The mode line appears at the bottom of the window. It is
549 full of dashes, to emphasize the boundaries between windows,
550 and is displayed in inverse video if the terminal supports it.
551 The information usually available includes:
553 *** Local Modes feature changed slightly.
555 GNU Emacs supports local mode lists much like those in Twenex Emacs,
556 but you can only set variables, not commands. You write
558 Local variables:
559 tab-width: 10
560 end:
562 in the last page of a file, if you want to make tab-width be ten in a
563 file's buffer. The value you specify must be a Lisp object!
564 It will be read, but not evaluated. So, to specify a string,
565 you MUST use doublequotes. For "false", in variables whose
566 meanings are true or false, you MUST write nil .
568 Two variable names are special: "mode" and "eval".
569 Mode is used for specifying the major mode (as in Twenex Emacs).
571 mode: text
573 specifies text mode. Eval is used for requesting the evaluation
574 of a Lisp expression; its value is ignored. Thus,
576 eval: (set-syntax-table lisp-mode-syntax-table)
578 causes Lisp Mode syntax to be used.
581 Note that GNU Emacs looks for the string "Local variables:"
582 whereas Twenex Emacs looks for "Local modes:". This incompatibility
583 id deliberate, so that neither one will see local settings
584 intended for the other.
586 *** Lisp code libraries.
588 Libraries of commands, and init files, are written in Lisp.
589 libraries conventionally have names ending in .el, while the
590 init file is named .emacs and is in your home directory.
592 Use Meta-x load-library to load a library. Most standard libraries
593 load automatically if you try to use the commands in them.
595 Meta-x byte-compile-file filename
596 compiles the file into byte code which loads and runs faster
597 than Lisp source code. The file of byte code is given a name
598 made by appending "c" to the end of the input file name.
600 Meta-x byte-recompile-directory directoryname
601 compiles all files in the specified directory (globbing not allowed)
602 which have been compiled before but have been changed since then.
604 Meta-x load-library automatically checks for a compiled file
605 before loading the source file.
607 Libraries once loaded do not retain their identity within GNU
608 Emacs. Therefore, you cannot tell just what was loaded from a
609 library, and you cannot un-load a library. Normally, libraries
610 are written so that loading one has no effect on the editing
611 operations that you would have used if you had not loaded the
612 library.
614 *** Dired features.
616 You can do dired on partial directories --- any pattern
617 the shell can glob. Dired creates a buffer named after
618 the directory or pattern, so you can dired several different
619 directories. If you repeat dired on the same directory or
620 pattern, it just reselects the same buffer. Use Meta-x Revert
621 on that buffer to read in the current contents of the directory.
623 *** Directory listing features.
625 C-x C-d now uses the default output format of `ls',
626 which gives just file names in multiple columns.
627 C-u C-x C-d passes the -l switch to `ls'.
629 Both read a directory spec from the minibuffer. It can
630 be any pattern that the shell can glob.
632 *** Compiling other programs.
634 Meta-x compile allows you to run make, or any other compilation
635 command, underneath GNU Emacs. Error messages go into a buffer whose
636 name is *compilation*. If you get error messages, you can use the
637 command C-x ` (that is a backquote) to find the text of the next
638 error message.
640 You must specify the command to be run as an argument to M-x compile.
641 A default is placed in the minibuffer; you can kill it and start
642 fresh, edit it, or just type Return if it is what you want.
643 The default is the last compilation command you used; initially,
644 it is "make -k".
646 *** Searching multiple files.
648 Meta-x grep searches many files for a regexp by invoking grep
649 and reading the output of grep into a buffer. You can then
650 move to the text lines that grep found, using the C-x ` command
651 just as after M-x compile.
653 *** Running inferior shells.
655 Do Meta-x shell to make an inferior shell together with a buffer
656 which serves to hold "terminal" input and output of the shell.
657 The shell used is specified by the environment variable ESHELL,
658 or by SHELL if ESHELL is not set.
660 Use C-h m whilst in the *shell* buffer to get more detailed info.
662 The inferior shell loads the file .emacs_csh or.emacs_sh
663 (or similar using whatever name the shell has) when it starts up.
665 M-! executes a shell command in an inferior shell
666 and displays the output from it. With a prefix argument,
667 it inserts the output in the current buffer after dot
668 and sets the mark after the output. The shell command
669 gets /dev/null as its standard input.
671 M-| is like M-! but passes the contents of the region
672 as input to the shell command. A prefix argument makes
673 the output from the command replace the contents of the region.
675 *** Sending mail.
677 Once you enter Mail Mode using C-x m or C-x 4 m or M-x mail,
678 C-c becomes a prefix character for mail-related editing commands.
679 C-c C-s is vital; that's how you send the message. C-c C-c sends
680 and then switches buffers or kills the current window.
681 Use C-h m to get a list of the others.
683 *** Regular expressions.
685 GNU Emacs has regular expression facilities like those of most
686 Unix editors, but more powerful:
688 **** -- + --
690 + specifies repetition of the preceding expression 1 or more
691 times. It is in other respect like *, which specifies repetition
692 0 or more times.
694 **** -- ? --
696 ? is like * but matches at most one repetition of the preceding
697 expression.
699 **** -- \| --
701 \| specifies an alternative. Two regular expressions A and B with \| in
702 between form an expression that matches anything that either A or B will
703 match. Thus, "foo\|bar" matches either "foo" or "bar" but no other
704 string.
706 \| applies to the larges possible surrounding expressions. Only a
707 surrounding \( ... \) grouping can limit the grouping power of \|.
709 Full backtracking capability exists when multiple \|'s are used.
711 **** -- \( ... \) --
713 \( ... \) are a grouping construct that serves three purposes:
715 1. To enclose a set of \| alternatives for other operations.
716 Thus, "\(foo\|bar\)x" matches either "foox" or "barx".
717 2. To enclose a complicated expression for * to operate on.
718 Thus, "ba\(na\)*" matches "bananana", etc., with any number
719 of na's (zero or more).
720 3. To mark a matched substring for future reference.
722 Application 3 is not a consequence of the idea of a parenthetical
723 grouping; it is a separate feature which happens to be assigned as a
724 second meaning to the same \( ... \) construct because there is no
725 conflict in practice between the two meanings. Here is an explanation
726 of this feature.
728 -- \digit --
730 After the end of a \( ... \) construct, the matcher remembers the
731 beginning and end of the text matched by that construct. Then, later on
732 in the regular expression, you can use \ followed by a digit to mean,
733 ``match the same text matched this time by the \( ... \) construct.''
734 The first nine \( ... \) constructs that appear in a regular expression
735 are assigned numbers 1 through 9 in order of their beginnings. \1
736 through \9 can be used to refer to the text matched by the corresponding
737 \( ... \) construct.
739 For example, "\(.*\)\1" matches any string that is composed of two
740 identical halves. The "\(.*\)" matches the first half, which can be
741 anything, but the \1 that follows must match the same exact text.
743 **** -- \` --
745 Matches the empty string, but only if it is at the beginning of the buffer.
747 **** -- \' --
749 Matches the empty string, but only if it is at the end of the buffer.
751 **** -- \b --
753 Matches the empty string, but only if it is at the beginning or end of
754 a word. Thus, "\bfoo\b" matches any occurrence of "foo" as a separate word.
755 "\bball\(s\|\)\b" matches "ball" or "balls" as a separate word.
757 **** -- \B --
759 Matches the empty string, provided it is NOT at the beginning or end of
760 a word.
762 **** -- \< --
764 Matches the empty string, provided it is at the beginning of a word.
766 **** -- \> --
768 Matches the empty string, provided it is at the end of a word.
770 **** -- \w --
772 Matches any word-constituent character. The editor syntax table determines
773 which characters these are.
775 **** -- \W --
777 Matches any character that is not a word-constituent.
779 **** -- \s<code> --
781 Matches any character whose syntax is <code>. <code> is a letter that
782 represents a syntax code: thus, "w" for word constituent, "-" for
783 whitespace, "(" for open-parenthesis, etc. Thus, "\s(" matches any
784 character with open-parenthesis syntax.
786 **** -- \S<code> --
788 Matches any character whose syntax is not <code>.
790 * How is this Emacs different from Gosling Emacs?
792 ** Advantages of Gosling Emacs:
794 1. The program itself is much smaller.
795 GNU Emacs uses about 250k more pure storage.
796 As a result, Gosling Emacs can run on machines
797 that cannot run GNU Emacs. There is not much difference
798 in the amount of impure storage in the two programs.
800 2. In some versions there is support for other forks to
801 establish communications channels to Emacs (using sockets?).
803 3. There is a direct interface to dbm (data bases).
805 ** Advantages of GNU Emacs:
807 *** True Lisp, not Mocklisp.
809 GNU Emacs's extension language has real symbols, lists
810 and vectors. Many extensions are much simpler, and some
811 become possible that were nearly impossible in Gosling Emacs.
812 Many primitives can have cleaner interfaces, and some features
813 need not be put in as special primitives because you can do
814 them easily yourself.
816 *** But Mocklisp still works.
818 An automatic conversion package plus a run-time library
819 allows you to convert a Mocklisp library into a Lisp library.
821 *** Commands are better crafted.
823 For example, nearly every editing function for which a
824 numeric argument would make sense as a repeat count does
825 accept a repeat count, and does handle a negative argument
826 in the way you would expect.
828 *** The manual is clearer.
830 Everyone tells me it is a very good manual.
832 *** Better on-line documentation.
834 Both functions and variables have documentation strings that
835 describe exactly how to use them.
837 *** C mode is smart.
839 It really knows how to indent each line correctly,
840 for most popular indentation styles. (Some variables
841 control which style is used; popular named styles are also supported.)
843 *** Compatible with PDP-10 Emacs, Multics Emacs and Zmacs.
845 The commands in GNU Emacs are nearly the same as in the
846 original Emacs and the other Emacses which imitated it.
847 (A few have been changed to fit the Unix environment better.)
849 *** Support for Gosling's Emacs commands.
851 M-x set-gosmacs-bindings rebinds many editing commands for
852 compatibility with Gosling's Emacs.
853 M-x set-gnu-bindings reverses the change.
855 *** Side-by-side windows.
857 You can split a GNU Emacs window either horizontally or
858 vertically.
860 *** Redisplay is faster.
862 GNU Emacs sends about the same stuff to the terminal that
863 Gosling's does, but GNU Emacs uses much less CPU time to
864 decide what to do.
866 *** Entirely termcap-driven.
868 GNU Emacs has nearly no special code for any terminal type. Various
869 new termcap strings make it possible to handle all terminals nearly as
870 fast as they could be handled by special-case code.
872 *** Display-hiding features.
874 For example, Outline Mode makes it possible for you to edit
875 an outline, making entire sub-branches of the outline visible
876 or invisible when you wish.
878 *** You can interrupt with Control-G.
880 Even a looping Lisp program can be stopped this way.
881 And even a loop in C code does not stop you from killing
882 Emacs and getting back to your shell.
884 *** Per-buffer Undo.
886 You can undo the last several changes, in each buffer
887 independently.
889 *** The editor code itself is clean.
891 Many people have remarked on how much they enjoy reading
892 the code for GNU Emacs.
894 One other note: The program etc/cvtmail that comes with GNU Emacs can
895 be used to convert a mail directory for Gosling Emacs's Rmail into a
896 Unix mail file that you could read into GNU Emacs's Rmail.
898 * How is this Emacs different from CCA Emacs?
900 ** GNU Emacs Lisp vs CCA Elisp.
902 GNU Emacs Lisp does not have a distinction between Lisp functions
903 and Emacs functions, or between Lisp variables and Emacs variables.
904 The Lisp and the editor are integrated. A Lisp function defined
905 with defun is callable as an editor command if you put an
906 interactive calling spec in it; for example,
907 (defun forward-character (n)
908 (interactive "p")
909 (goto-char (+ (point) n)))
910 defines a function of one argument that moves point forward by
911 a specified number of characters. Programs could call this function,
912 as in (forward-character 6), or it could be assigned to a key,
913 in which case the "p" says to pass the prefix numeric arg as
914 the function's argument. As a result of this feature, you often
915 need not have two different functions, one to be called by programs
916 and another to read arguments from the user conveniently; the same
917 function can do both.
919 CCA Elisp tries to be a subset of Common Lisp and tries to
920 have as many Common Lisp functions as possible (though it is still
921 only a small fraction of full Common Lisp). GNU Emacs Lisp
922 is somewhat similar to Common Lisp just because of my Maclisp
923 and Lisp Machine background, but it has several distinct incompatibilities
924 in both syntax and semantics. Also, I have not attempted to
925 provide many Common Lisp functions that you could write in Lisp,
926 or others that provide no new capability in the circumstances.
928 GNU Emacs Lisp does not have packages, readtables, or character objects
929 (it uses integers to represent characters).
931 On the other hand, windows, buffers, relocatable markers and processes
932 are first class objects in GNU Emacs Lisp. You can get information about them
933 and do things to them in a Lispy fashion. Not so in CCA Emacs.
935 In GNU Emacs Lisp, you cannot open a file and read or write characters
936 or Lisp objects from it. This feature is painful to support, and
937 is not fundamentally necessary in an Emacs, because instead you
938 can read the file into a buffer, read or write characters or
939 Lisp objects in the buffer, and then write the buffer into the file.
941 On the other hand, GNU Emacs Lisp does allow you to rename, delete, add
942 names to, and copy files; also to find out whether a file is a
943 directory, whether it is a symbolic link and to what name, whether
944 you can read it or write it, find out its directory component,
945 expand a relative pathname, find completions of a file name, etc.,
946 which you cannot do in CCA Elisp.
948 GNU Emacs Lisp uses dynamic scope exclusively. This enables you to
949 bind variables which affect the execution of the editor, such as
950 indent-tabs-mode.
952 GNU Emacs Lisp code is normally compiled into byte code. Most of the
953 standard editing commands are written in Lisp, and many are
954 dumped, pure, in the Emacs that users normally run.
956 GNU Emacs allows you to interrupt a runaway Lisp program with
957 Control-g.
959 ** GNU Emacs Editing Advantages
961 GNU Emacs is faster for many things, especially insertion of text
962 and file I/O.
964 GNU Emacs allows you to undo more than just the last command
965 with the undo command (C-x u, or C-_). You can undo quite a ways back.
966 Undo information is separate for each buffer; changes in one buffer
967 do not affect your ability to undo in another buffer.
969 GNU Emacs commands that want to display some output do so by putting
970 it in a buffer and displaying that buffer in a window. This
971 technique comes from Gosling Emacs. It has both advantages and
972 disadvantages when compared with the technique, copied by CCA Emacs
973 from my original Emacs which inherited it from TECO, of having "type
974 out" which appears on top of the text in the current window but
975 disappears automatically at the next input character.
977 GNU Emacs does not use the concept of "subsystems". Instead, it uses
978 highly specialized major modes. For example, dired in GNU Emacs has
979 the same commands as dired does in other versions of Emacs, give or
980 take a few, but it is a major mode, not a subsystem. The advantage
981 of this is that you do not have to "exit" from dired and lose the
982 state of dired in order to edit files again. You can simply switch
983 to another buffer, and switch back to the dired buffer later. You
984 can also have several dired buffers, looking at different directories.
986 It is still possible to write a subsystem--your own command loop--
987 in GNU Emacs, but it is not recommended, since writing a major mode
988 for a special buffer is better.
990 Recursive edits are also rarely used, for the same reason: it is better
991 to make a new buffer and put it in a special major mode. Sending
992 mail is done this way.
994 GNU Emacs expects everyone to use find-file (C-x C-f) for reading
995 in files; its C-x C-v command kills the current buffer and then finds
996 the specified file.
998 As a result, users do not need to think about the complexities
999 of subsystems, recursive edits, and various ways to read in files
1000 or what to do if a buffer contains changes to some other file.
1002 GNU Emacs uses its own format of tag table, made by the "etags"
1003 program. This format makes finding a tag much faster.
1005 Dissociated Press is supported.
1008 ** GNU Emacs Editing Disadvantages.
1010 GNU Emacs does not display the location of the mark.
1012 GNU Emacs does not have a concept of numbers of buffers,
1013 or a permanent ordering of buffers, or searching through multiple
1014 buffers. The tags-search command provides a way to search
1015 through several buffers automatically.
1017 GNU Emacs does not provide commands to visit files without
1018 setting the buffer's default directory. Users can write such
1019 commands in Lisp by copying the code of the standard file
1020 visiting commands and modifying them.
1022 GNU Emacs does not support "plus options" in the command
1023 arguments or in buffer-selection commands, except for line numbers.
1025 GNU Emacs does not support encryption. Down with security!
1027 GNU Emacs does not support replaying keystroke files,
1028 and does not normally write keystroke files.
1031 ** Neutral Differences
1033 GNU Emacs uses TAB, not ESC, to complete file names, buffer names,
1034 command names, etc.
1036 GNU Emacs uses LFD to terminate searches, instead of
1037 the C-d uses by CCA Emacs. (Actually, this character is controlled
1038 by a parameter in GNU Emacs.) C-M-s in GNU Emacs is an interactive
1039 regular expression search, but you can get to a noninteractive
1040 one by typing ESC right after the C-M-s.
1042 In GNU Emacs, C-x s asks, for each modified file buffer, whether
1043 to save it.
1045 GNU Emacs indicates line continuation with "\" and line
1046 truncation (at either margin) with "$".
1048 The command to resume a tags-search or tags-query-replace in
1049 GNU Emacs is Meta-Comma.