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早期freebsd实现

YOU WILL LOSE: C mode does not know a function starts there.

Open-brace at the beginning of a line makes it possible
for C mode to find function boundaries with total reliability;
something I consider vital and which cannot be done
if the other style is used.

The Tab command indents C code very cleverly.
I know of only one cases in which Tab does not indent C code nicely:
 Expressions continued over several lines with few parentheses.
 Tab does not know the precedences of C operators, so it does
 not know which lines of the expression should go where.
 Using parentheses to indicate the nesting of operators
 except within a line makes this problem go away.

The indenting algorithm is entirely written in Lisp.

Tab with a numeric argument in Twenex Emacs indents
that many lines.  It is different in GNU Emacs: it means
to shift all the lines of a bracketed expression by the
same amount as the line being indented.  For example, if you have
    if (foo)
        {
	    hack ();
	     /** Well? */
	}
and type C-u Tab on the line with the open brace, you get
    if (foo)
      {
	  hack ();
	   /* Well? */
      }
from indenting the brace line and then shifting the
lines within the braces rigidly with the first one.

Meta-Control-q works as in Lisp mode; it should be
used with dot just before a bracketed grouping, and
indents each line INSIDE that grouping using Tab.
If used instead of C-u Tab in the previous example, it makes
    if (foo)
        {
	  hack ();
	  /* Well? */
	}

Meta-Control-h puts mark at the end of the current C function
and puts dot before it.

Most other Meta-Control commands intended for Lisp expressions
work usefully in C mode as well.

** Meta-g (fill-region) is different.

In Twenex Emacs, Meta-g fills the region with no paragraph
boundaries except for blank and indented lines.  In GNU Emacs,
it divides the region into paragraphs in the same manner as
Meta-], and fills each paragraph separately.  There is also
the function fill-region-as-paragraph which fills the region
regarding at as a single paragraph regardless even of blank
or indented lines.

** Indented Text Mode instead of Edit Indented Text.

Twenex Emacs has a command Edit Indented Text which temporarily
alters some commands for editing indented paragraphs.
GNU Emacs has instead a separate major mode, Indented Text Mode,
which is different from ordinary Text Mode in just the same
alterations.  Specifically, in Indented Text Mode,
Tab runs the function indent-relative, and auto filling indents
the newly created lines.

** But rectangle commands are implemented.

C-x r stores the rectangle described by dot and mark
into a register; it reads the register name from the keyboard.
C-x g, the command to insert the contents of a register,
can be used to reinsert the rectangle elsewhere.

Other rectangle commands include
  open-rectangle:
    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>.