This is ../info/emacs, produced by makeinfo version 4.0 from emacs.texi.

   This is the thirteenth edition of the `GNU Emacs Manual', updated
for Emacs version 20.7.

INFO-DIR-SECTION Editors
START-INFO-DIR-ENTRY
* Emacs: (emacs).	The extensible self-documenting text editor.
END-INFO-DIR-ENTRY

   Published by the Free Software Foundation 59 Temple Place, Suite 330
Boston, MA  02111-1307 USA

   Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1996, 1997, 1998,
1999    Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
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   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the sections entitled "The GNU Manifesto", "Distribution" and "GNU
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provided that the entire resulting derived work is distributed under the
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   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that the sections entitled "The GNU Manifesto",
"Distribution" and "GNU General Public License" may be included in a
translation approved by the Free Software Foundation instead of in the
original English.


File: emacs,  Node: Variables for C Indent,  Next: C Indent Styles,  Prev: Syntactic Symbols,  Up: Custom C Indent

Variables for C Indentation
...........................

   This section describes additional variables which control the
indentation behavior of C mode and related mode.

`c-offsets-alist'
     Association list of syntactic symbols and their indentation
     offsets.  You should not set this directly, only with
     `c-set-offset'.  *Note Changing Indent Style::, for details.

`c-style-alist'
     Variable for defining indentation styles; see below.

`c-basic-offset'
     Amount of basic offset used by `+' and `-' symbols in
     `c-offsets-alist'.

`c-special-indent-hook'
     Hook for user-defined special indentation adjustments.  This hook
     is called after a line is indented by C mode and related modes.

   The variable `c-style-alist' specifies the predefined indentation
styles.  Each element has form `(NAME VARIABLE-SETTING...)', where NAME
is the name of the style.  Each VARIABLE-SETTING has the form `(VARIABLE
. VALUE)'; VARIABLE is one of the customization variables used by C
mode, and VALUE is the value for that variable when using the selected
style.

   When VARIABLE is `c-offsets-alist', that is a special case: VALUE is
appended to the front of the value of `c-offsets-alist' instead of
replacing that value outright.  Therefore, it is not necessary for
VALUE to specify each and every syntactic symbol--only those for which
the style differs from the default.

   The indentation of lines containing only comments is also affected by
the variable `c-comment-only-line-offset' (*note Comments in C::).


File: emacs,  Node: C Indent Styles,  Prev: Variables for C Indent,  Up: Custom C Indent

C Indentation Styles
....................

   A "C style" is a collection of indentation style customizations.
Emacs comes with several predefined indentation styles for C and related
modes, including `gnu', `k&r', `bsd', `stroustrup', `linux', `python',
`java', `whitesmith', `ellemtel', and `cc-mode'.  The default style is
`gnu'.

   To choose the style you want, use the command `M-x c-set-style'.
Specify a style name as an argument (case is not significant in C style
names).  The chosen style only affects newly visited buffers, not those
you are already editing.  You can also set the variable
`c-default-style' to specify the style for various major modes.  Its
value should be an alist, in which each element specifies one major
mode and which indentation style to use for it.  For example,

     (setq c-default-style
           '((java-mode . "java") (other . "gnu")))

specifies an explicit choice for Java mode, and the default `gnu' style
for the other C-like modes.

   To define a new C indentation style, call the function `c-add-style':

     (c-add-style NAME VALUES USE-NOW)

Here NAME is the name of the new style (a string), and VALUES is an
alist whose elements have the form `(VARIABLE . VALUE)'.  The variables
you specify should be among those documented in *Note Variables for C
Indent::.

   If USE-NOW is non-`nil', `c-add-style' switches to the new style
after defining it.


File: emacs,  Node: Matching,  Next: Comments,  Prev: Program Indent,  Up: Programs

Automatic Display Of Matching Parentheses
=========================================

   The Emacs parenthesis-matching feature is designed to show
automatically how parentheses match in the text.  Whenever you type a
self-inserting character that is a closing delimiter, the cursor moves
momentarily to the location of the matching opening delimiter, provided
that is on the screen.  If it is not on the screen, some text near it is
displayed in the echo area.  Either way, you can tell what grouping is
being closed off.

   In Lisp, automatic matching applies only to parentheses.  In C, it
applies to braces and brackets too.  Emacs knows which characters to
regard as matching delimiters based on the syntax table, which is set
by the major mode.  *Note Syntax::.

   If the opening delimiter and closing delimiter are mismatched--such
as in `[x)'--a warning message is displayed in the echo area.  The
correct matches are specified in the syntax table.

   Three variables control parenthesis match display.
`blink-matching-paren' turns the feature on or off; `nil' turns it off,
but the default is `t' to turn match display on.
`blink-matching-delay' says how many seconds to wait; the default is 1,
but on some systems it is useful to specify a fraction of a second.
`blink-matching-paren-distance' specifies how many characters back to
search to find the matching opening delimiter.  If the match is not
found in that far, scanning stops, and nothing is displayed.  This is
to prevent scanning for the matching delimiter from wasting lots of
time when there is no match.  The default is 12,000.

   When using X Windows, you can request a more powerful alternative
kind of automatic parenthesis matching by enabling Show Paren mode.
This mode turns off the usual kind of matching parenthesis display and
instead uses highlighting to show what matches.  Whenever point is after
a close parenthesis, the close parenthesis and its matching open
parenthesis are both highlighted; otherwise, if point is before an open
parenthesis, the matching close parenthesis is highlighted.  (There is
no need to highlight the open parenthesis after point because the cursor
appears on top of that character.)  Use the command `M-x
show-paren-mode' to enable or disable this mode.


File: emacs,  Node: Comments,  Next: Balanced Editing,  Prev: Matching,  Up: Programs

Manipulating Comments
=====================

   Because comments are such an important part of programming, Emacs
provides special commands for editing and inserting comments.

* Menu:

* Comment Commands::
* Multi-Line Comments::
* Options for Comments::


File: emacs,  Node: Comment Commands,  Next: Multi-Line Comments,  Up: Comments

Comment Commands
----------------

   The comment commands insert, kill and align comments.

`M-;'
     Insert or align comment (`indent-for-comment').

`C-x ;'
     Set comment column (`set-comment-column').

`C-u - C-x ;'
     Kill comment on current line (`kill-comment').

`C-M-j'
     Like <RET> followed by inserting and aligning a comment
     (`indent-new-comment-line').

`M-x comment-region'
     Add or remove comment delimiters on all the lines in the region.

   The command that creates a comment is `M-;' (`indent-for-comment').
If there is no comment already on the line, a new comment is created,
aligned at a specific column called the "comment column".  The comment
is created by inserting the string Emacs thinks comments should start
with (the value of `comment-start'; see below).  Point is left after
that string.  If the text of the line extends past the comment column,
then the indentation is done to a suitable boundary (usually, at least
one space is inserted).  If the major mode has specified a string to
terminate comments, that is inserted after point, to keep the syntax
valid.

   `M-;' can also be used to align an existing comment.  If a line
already contains the string that starts comments, then `M-;' just moves
point after it and reindents it to the conventional place.  Exception:
comments starting in column 0 are not moved.

   Some major modes have special rules for indenting certain kinds of
comments in certain contexts.  For example, in Lisp code, comments which
start with two semicolons are indented as if they were lines of code,
instead of at the comment column.  Comments which start with three
semicolons are supposed to start at the left margin.  Emacs understands
these conventions by indenting a double-semicolon comment using <TAB>,
and by not changing the indentation of a triple-semicolon comment at
all.

     ;; This function is just an example
     ;;; Here either two or three semicolons are appropriate.
     (defun foo (x)
     ;;; And now, the first part of the function:
       ;; The following line adds one.
       (1+ x))           ; This line adds one.

   In C code, a comment preceded on its line by nothing but whitespace
is indented like a line of code.

   Even when an existing comment is properly aligned, `M-;' is still
useful for moving directly to the start of the comment.

   `C-u - C-x ;' (`kill-comment') kills the comment on the current line,
if there is one.  The indentation before the start of the comment is
killed as well.  If there does not appear to be a comment in the line,
nothing is done.  To reinsert the comment on another line, move to the
end of that line, do `C-y', and then do `M-;' to realign it.  Note that
`C-u - C-x ;' is not a distinct key; it is `C-x ;'
(`set-comment-column') with a negative argument.  That command is
programmed so that when it receives a negative argument it calls
`kill-comment'.  However, `kill-comment' is a valid command which you
could bind directly to a key if you wanted to.


File: emacs,  Node: Multi-Line Comments,  Next: Options for Comments,  Prev: Comment Commands,  Up: Comments

Multiple Lines of Comments
--------------------------

   If you are typing a comment and wish to continue it on another line,
you can use the command `C-M-j' (`indent-new-comment-line').  This
terminates the comment you are typing, creates a new blank line
afterward, and begins a new comment indented under the old one.  When
Auto Fill mode is on, going past the fill column while typing a comment
causes the comment to be continued in just this fashion.  If point is
not at the end of the line when `C-M-j' is typed, the text on the rest
of the line becomes part of the new comment line.

   To turn existing lines into comment lines, use the `M-x
comment-region' command.  It adds comment delimiters to the lines that
start in the region, thus commenting them out.  With a negative
argument, it does the opposite--it deletes comment delimiters from the
lines in the region.

   With a positive argument, `comment-region' duplicates the last
character of the comment start sequence it adds; the argument specifies
how many copies of the character to insert.  Thus, in Lisp mode, `C-u 2
M-x comment-region' adds `;;' to each line.  Duplicating the comment
delimiter is a way of calling attention to the comment.  It can also
affect how the comment is indented.  In Lisp, for proper indentation,
you should use an argument of two, if between defuns, and three, if
within a defun.

   The variable `comment-padding' specifies how many spaces
`comment-region' should insert on each line between the comment
delimiter and the line's original text.  The default is 1.


File: emacs,  Node: Options for Comments,  Prev: Multi-Line Comments,  Up: Comments

Options Controlling Comments
----------------------------

   The comment column is stored in the variable `comment-column'.  You
can set it to a number explicitly.  Alternatively, the command `C-x ;'
(`set-comment-column') sets the comment column to the column point is
at.  `C-u C-x ;' sets the comment column to match the last comment
before point in the buffer, and then does a `M-;' to align the current
line's comment under the previous one.  Note that `C-u - C-x ;' runs
the function `kill-comment' as described above.

   The variable `comment-column' is per-buffer: setting the variable in
the normal fashion affects only the current buffer, but there is a
default value which you can change with `setq-default'.  *Note
Locals::.  Many major modes initialize this variable for the current
buffer.

   The comment commands recognize comments based on the regular
expression that is the value of the variable `comment-start-skip'.
Make sure this regexp does not match the null string.  It may match more
than the comment starting delimiter in the strictest sense of the word;
for example, in C mode the value of the variable is `"/\\*+ *"', which
matches extra stars and spaces after the `/*' itself.  (Note that `\\'
is needed in Lisp syntax to include a `\' in the string, which is
needed to deny the first star its special meaning in regexp syntax.
*Note Regexps::.)

   When a comment command makes a new comment, it inserts the value of
`comment-start' to begin it.  The value of `comment-end' is inserted
after point, so that it will follow the text that you will insert into
the comment.  In C mode, `comment-start' has the value `"/* "' and
`comment-end' has the value `" */"'.

   The variable `comment-multi-line' controls how `C-M-j'
(`indent-new-comment-line') behaves when used inside a comment.  If
`comment-multi-line' is `nil', as it normally is, then the comment on
the starting line is terminated and a new comment is started on the new
following line.  If `comment-multi-line' is not `nil', then the new
following line is set up as part of the same comment that was found on
the starting line.  This is done by not inserting a terminator on the
old line, and not inserting a starter on the new line.  In languages
where multi-line comments work, the choice of value for this variable
is a matter of taste.

   The variable `comment-indent-function' should contain a function
that will be called to compute the indentation for a newly inserted
comment or for aligning an existing comment.  It is set differently by
various major modes.  The function is called with no arguments, but with
point at the beginning of the comment, or at the end of a line if a new
comment is to be inserted.  It should return the column in which the
comment ought to start.  For example, in Lisp mode, the indent hook
function bases its decision on how many semicolons begin an existing
comment, and on the code in the preceding lines.


File: emacs,  Node: Balanced Editing,  Next: Symbol Completion,  Prev: Comments,  Up: Programs

Editing Without Unbalanced Parentheses
======================================

`M-('
     Put parentheses around next sexp(s) (`insert-parentheses').

`M-)'
     Move past next close parenthesis and reindent
     (`move-past-close-and-reindent').

   The commands `M-(' (`insert-parentheses') and `M-)'
(`move-past-close-and-reindent') are designed to facilitate a style of
editing which keeps parentheses balanced at all times.  `M-(' inserts a
pair of parentheses, either together as in `()', or, if given an
argument, around the next several sexps.  It leaves point after the
open parenthesis.  The command `M-)' moves past the close parenthesis,
deleting any indentation preceding it, and indenting with `C-j' after
it.

   For example, instead of typing `( F O O )', you can type `M-( F O
O', which has the same effect except for leaving the cursor before the
close parenthesis.

   `M-(' may insert a space before the open parenthesis, depending on
the syntax class of the preceding character.  Set
`parens-require-spaces' to `nil' value if you wish to inhibit this.


File: emacs,  Node: Symbol Completion,  Next: Which Function,  Prev: Balanced Editing,  Up: Programs

Completion for Symbol Names
===========================

   Usually completion happens in the minibuffer.  But one kind of
completion is available in all buffers: completion for symbol names.

   The character `M-<TAB>' runs a command to complete the partial
symbol before point against the set of meaningful symbol names.  Any
additional characters determined by the partial name are inserted at
point.

   If the partial name in the buffer has more than one possible
completion and they have no additional characters in common, a list of
all possible completions is displayed in another window.

   In most programming language major modes, `M-<TAB>' runs the command
`complete-symbol', which provides two kinds of completion.  Normally it
does completion based on a tags table (*note Tags::); with a numeric
argument (regardless of the value), it does completion based on the
names listed in the Info file indexes for your language.  Thus, to
complete the name of a symbol defined in your own program, use
`M-<TAB>' with no argument; to complete the name of a standard library
function, use `C-u M-<TAB>'.  Of course, Info-based completion works
only if there is an Info file for the standard library functions of
your language, and only if it is installed at your site.

   In Emacs-Lisp mode, the name space for completion normally consists
of nontrivial symbols present in Emacs--those that have function
definitions, values or properties.  However, if there is an
open-parenthesis immediately before the beginning of the partial symbol,
only symbols with function definitions are considered as completions.
The command which implements this is `lisp-complete-symbol'.

   In Text mode and related modes, `M-<TAB>' completes words based on
the spell-checker's dictionary.  *Note Spelling::.


File: emacs,  Node: Which Function,  Next: Documentation,  Prev: Symbol Completion,  Up: Programs

Which Function Mode
===================

   Which Function mode is a minor mode that displays the current
function name in the mode line, as you move around in a buffer.

   To enable (or disable) Which Function mode, use the command `M-x
which-function-mode'.  This command is global; it applies to all
buffers, both existing ones and those yet to be created.  However, this
only affects certain major modes, those listed in the value of
`which-func-modes'.  (If the value is `t', then Which Function mode
applies to all major modes that know how to support it--which are the
major modes that support Imenu.)


File: emacs,  Node: Documentation,  Next: Change Log,  Prev: Which Function,  Up: Programs

Documentation Commands
======================

   As you edit Lisp code to be run in Emacs, the commands `C-h f'
(`describe-function') and `C-h v' (`describe-variable') can be used to
print documentation of functions and variables that you want to call.
These commands use the minibuffer to read the name of a function or
variable to document, and display the documentation in a window.

   For extra convenience, these commands provide default arguments
based on the code in the neighborhood of point.  `C-h f' sets the
default to the function called in the innermost list containing point.
`C-h v' uses the symbol name around or adjacent to point as its default.

   For Emacs Lisp code, you can also use Eldoc mode.  This minor mode
constantly displays in the echo area the argument list for the function
being called at point.  (In other words, it finds the function call that
point is contained in, and displays the argument list of that function.)
Eldoc mode applies in Emacs Lisp and Lisp Interaction modes only.  Use
the command `M-x eldoc-mode' to enable or disable this feature.

   For C, Lisp, and other languages, you can use `C-h C-i'
(`info-lookup-symbol') to view the Info documentation for a symbol.
You specify the symbol with the minibuffer; by default, it uses the
symbol that appears in the buffer at point.  The major mode determines
where to look for documentation for the symbol--which Info files and
which indices.  You can also use `M-x info-lookup-file' to look for
documentation for a file name.

   You can read the "man page" for an operating system command, library
function, or system call, with the `M-x manual-entry' command.  It runs
the `man' program to format the man page, and runs it asynchronously if
your system permits, so that you can keep on editing while the page is
being formatted.  (MS-DOS and MS-Windows 3 do not permit asynchronous
subprocesses, so on these systems you cannot edit while Emacs waits for
`man' to exit.)  The result goes in a buffer named `*Man TOPIC*'.
These buffers use a special major mode, Man mode, that facilitates
scrolling and examining other manual pages.  For details, type `C-h m'
while in a man page buffer.

   For a long man page, setting the faces properly can take substantial
time.  By default, Emacs uses faces in man pages if Emacs can display
different fonts or colors.  You can turn off use of faces in man pages
by setting the variable `Man-fontify-manpage-flag' to `nil'.

   If you insert the text of a man page into an Emacs buffer in some
other fashion, you can use the command `M-x Man-fontify-manpage' to
perform the same conversions that `M-x manual-entry' does.

   Eventually the GNU project hopes to replace most man pages with
better-organized manuals that you can browse with Info.  *Note Misc
Help::.  Since this process is only partially completed, it is still
useful to read manual pages.


File: emacs,  Node: Change Log,  Next: Tags,  Prev: Documentation,  Up: Programs

Change Logs
===========

   The Emacs command `C-x 4 a' adds a new entry to the change log file
for the file you are editing (`add-change-log-entry-other-window').

   A change log file contains a chronological record of when and why you
have changed a program, consisting of a sequence of entries describing
individual changes.  Normally it is kept in a file called `ChangeLog'
in the same directory as the file you are editing, or one of its parent
directories.  A single `ChangeLog' file can record changes for all the
files in its directory and all its subdirectories.

   A change log entry starts with a header line that contains your name,
your email address (taken from the variable `user-mail-address'), and
the current date and time.  Aside from these header lines, every line
in the change log starts with a space or a tab.  The bulk of the entry
consists of "items", each of which starts with a line starting with
whitespace and a star.  Here are two entries, both dated in May 1993,
each with two items:

     1993-05-25  Richard Stallman  <rms@gnu.org>
     
             * man.el: Rename symbols `man-*' to `Man-*'.
             (manual-entry): Make prompt string clearer.
     
             * simple.el (blink-matching-paren-distance):
             Change default to 12,000.
     
     1993-05-24  Richard Stallman  <rms@gnu.org>
     
             * vc.el (minor-mode-map-alist): Don't use it if it's void.
             (vc-cancel-version): Doc fix.

(Previous Emacs versions used a different format for the date.)

   One entry can describe several changes; each change should have its
own item.  Normally there should be a blank line between items.  When
items are related (parts of the same change, in different places), group
them by leaving no blank line between them.  The second entry above
contains two items grouped in this way.

   `C-x 4 a' visits the change log file and creates a new entry unless
the most recent entry is for today's date and your name.  It also
creates a new item for the current file.  For many languages, it can
even guess the name of the function or other object that was changed.

   The change log file is visited in Change Log mode.  In this major
mode, each bunch of grouped items counts as one paragraph, and each
entry is considered a page.  This facilitates editing the entries.
`C-j' and auto-fill indent each new line like the previous line; this
is convenient for entering the contents of an entry.

   Version control systems are another way to keep track of changes in
your program and keep a change log.  *Note Log Buffer::.


File: emacs,  Node: Tags,  Next: Emerge,  Prev: Change Log,  Up: Programs

Tags Tables
===========

   A "tags table" is a description of how a multi-file program is
broken up into files.  It lists the names of the component files and the
names and positions of the functions (or other named subunits) in each
file.  Grouping the related files makes it possible to search or replace
through all the files with one command.  Recording the function names
and positions makes possible the `M-.' command which finds the
definition of a function by looking up which of the files it is in.

   Tags tables are stored in files called "tags table files".  The
conventional name for a tags table file is `TAGS'.

   Each entry in the tags table records the name of one tag, the name
of the file that the tag is defined in (implicitly), and the position
in that file of the tag's definition.

   Just what names from the described files are recorded in the tags
table depends on the programming language of the described file.  They
normally include all functions and subroutines, and may also include
global variables, data types, and anything else convenient.  Each name
recorded is called a "tag".

* Menu:

* Tag Syntax::		Tag syntax for various types of code and text files.
* Create Tags Table::	Creating a tags table with `etags'.
* Select Tags Table::	How to visit a tags table.
* Find Tag::		Commands to find the definition of a specific tag.
* Tags Search::		Using a tags table for searching and replacing.
* List Tags::		Listing and finding tags defined in a file.


File: emacs,  Node: Tag Syntax,  Next: Create Tags Table,  Up: Tags

Source File Tag Syntax
----------------------

   Here is how tag syntax is defined for the most popular languages:

   * In C code, any C function or typedef is a tag, and so are
     definitions of `struct', `union' and `enum'.  `#define' macro
     definitions and `enum' constants are also tags, unless you specify
     `--no-defines' when making the tags table.  Similarly, global
     variables are tags, unless you specify `--no-globals'.  Use of
     `--no-globals' and `--no-defines' can make the tags table file
     much smaller.

   * In C++ code, in addition to all the tag constructs of C code,
     member functions are also recognized, and optionally member
     variables if you use the `--members' option.  Tags for variables
     and functions in classes are named `CLASS::VARIABLE' and
     `CLASS::FUNCTION'.

   * In Java code, tags include all the constructs recognized in C++,
     plus the `extends' and `implements' constructs.  Tags for variables
     and functions in classes are named `CLASS.VARIABLE' and
     `CLASS.FUNCTION'.

   * In LaTeX text, the argument of any of the commands `\chapter',
     `\section', `\subsection', `\subsubsection', `\eqno', `\label',
     `\ref', `\cite', `\bibitem', `\part', `\appendix', `\entry', or
     `\index', is a tag.

     Other commands can make tags as well, if you specify them in the
     environment variable `TEXTAGS' before invoking `etags'.  The value
     of this environment variable should be a colon-separated list of
     command names.  For example,

          TEXTAGS="def:newcommand:newenvironment"
          export TEXTAGS

     specifies (using Bourne shell syntax) that the commands `\def',
     `\newcommand' and `\newenvironment' also define tags.

   * In Lisp code, any function defined with `defun', any variable
     defined with `defvar' or `defconst', and in general the first
     argument of any expression that starts with `(def' in column zero,
     is a tag.

   * In Scheme code, tags include anything defined with `def' or with a
     construct whose name starts with `def'.  They also include
     variables set with `set!' at top level in the file.

   Several other languages are also supported:

   * In assembler code, labels appearing at the beginning of a line,
     followed by a colon, are tags.

   * In Bison or Yacc input files, each rule defines as a tag the
     nonterminal it constructs.  The portions of the file that contain
     C code are parsed as C code.

   * In Cobol code, tags are paragraph names; that is, any word
     starting in column 8 and followed by a period.

   * In Erlang code, the tags are the functions, records, and macros
     defined in the file.

   * In Fortran code, functions, subroutines and blockdata are tags.

   * In Objective C code, tags include Objective C definitions for
     classes, class categories, methods, and protocols.

   * In Pascal code, the tags are the functions and procedures defined
     in the file.

   * In Perl code, the tags are the procedures defined by the `sub'
     keyword.

   * In Postscript code, the tags are the functions.

   * In Prolog code, a tag name appears at the left margin.

   You can also generate tags based on regexp matching (*note Create
Tags Table::) to handle other formats and languages.


File: emacs,  Node: Create Tags Table,  Next: Select Tags Table,  Prev: Tag Syntax,  Up: Tags

Creating Tags Tables
--------------------

   The `etags' program is used to create a tags table file.  It knows
the syntax of several languages, as described in *Note Tag Syntax::.
Here is how to run `etags':

     etags INPUTFILES...

The `etags' program reads the specified files, and writes a tags table
named `TAGS' in the current working directory.  `etags' recognizes the
language used in an input file based on its file name and contents.
You can specify the language with the `--language=NAME' option,
described below.

   If the tags table data become outdated due to changes in the files
described in the table, the way to update the tags table is the same
way it was made in the first place.  It is not necessary to do this
often.

   If the tags table fails to record a tag, or records it for the wrong
file, then Emacs cannot possibly find its definition.  However, if the
position recorded in the tags table becomes a little bit wrong (due to
some editing in the file that the tag definition is in), the only
consequence is a slight delay in finding the tag.  Even if the stored
position is very wrong, Emacs will still find the tag, but it must
search the entire file for it.

   So you should update a tags table when you define new tags that you
want to have listed, or when you move tag definitions from one file to
another, or when changes become substantial.  Normally there is no need
to update the tags table after each edit, or even every day.

   One tags table can effectively include another.  Specify the included
tags file name with the `--include=FILE' option when creating the file
that is to include it.  The latter file then acts as if it contained
all the files specified in the included file, as well as the files it
directly contains.

   If you specify the source files with relative file names when you run
`etags', the tags file will contain file names relative to the
directory where the tags file was initially written.  This way, you can
move an entire directory tree containing both the tags file and the
source files, and the tags file will still refer correctly to the source
files.

   If you specify absolute file names as arguments to `etags', then the
tags file will contain absolute file names.  This way, the tags file
will still refer to the same files even if you move it, as long as the
source files remain in the same place.  Absolute file names start with
`/', or with `DEVICE:/' on MS-DOS and MS-Windows.

   When you want to make a tags table from a great number of files, you
may have problems listing them on the command line, because some systems
have a limit on its length.  The simplest way to circumvent this limit
is to tell `etags' to read the file names from its standard input, by
typing a dash in place of the file names, like this:

     find . -name "*.[chCH]" -print | etags -

   Use the option `--language=NAME' to specify the language explicitly.
You can intermix these options with file names; each one applies to
the file names that follow it.  Specify `--language=auto' to tell
`etags' to resume guessing the language from the file names and file
contents.  Specify `--language=none' to turn off language-specific
processing entirely; then `etags' recognizes tags by regexp matching
alone.  `etags --help' prints the list of the languages `etags' knows,
and the file name rules for guessing the language.

   The `--regex' option provides a general way of recognizing tags
based on regexp matching.  You can freely intermix it with file names.
Each `--regex' option adds to the preceding ones, and applies only to
the following files.  The syntax is:

     --regex=/TAGREGEXP[/NAMEREGEXP]/

where TAGREGEXP is used to match the lines to tag.  It is always
anchored, that is, it behaves as if preceded by `^'.  If you want to
account for indentation, just match any initial number of blanks by
beginning your regular expression with `[ \t]*'.  In the regular
expressions, `\' quotes the next character, and `\t' stands for the tab
character.  Note that `etags' does not handle the other C escape
sequences for special characters.

   The syntax of regular expressions in `etags' is the same as in
Emacs, augmented with the "interval operator", which works as in `grep'
and `ed'.  The syntax of an interval operator is `\{M,N\}', and its
meaning is to match the preceding expression at least M times and up to
N times.

   You should not match more characters with TAGREGEXP than that needed
to recognize what you want to tag.  If the match is such that more
characters than needed are unavoidably matched by TAGREGEXP, you may
find useful to add a NAMEREGEXP, in order to narrow the tag scope.  You
can find some examples below.

   The `-R' option deletes all the regexps defined with `--regex'
options.  It applies to the file names following it, as you can see
from the following example:

     etags --regex=/REG1/ voo.doo --regex=/REG2/ \
         bar.ber -R --lang=lisp los.er

Here `etags' chooses the parsing language for `voo.doo' and `bar.ber'
according to their contents.  `etags' also uses REG1 to recognize
additional tags in `voo.doo', and both REG1 and REG2 to recognize
additional tags in `bar.ber'.  `etags' uses the Lisp tags rules, and no
regexp matching, to recognize tags in `los.er'.

   Here are some more examples.  The regexps are quoted to protect them
from shell interpretation.

   * Tag the `DEFVAR' macros in the emacs source files:

          --regex='/[ \t]*DEFVAR_[A-Z_ \t(]+"\([^"]+\)"/'

   * Tag VHDL files (this example is a single long line, broken here for
     formatting reasons):

          --language=none
          --regex='/[ \t]*\(ARCHITECTURE\|CONFIGURATION\) +[^ ]* +OF/'
          --regex='/[ \t]*\(ATTRIBUTE\|ENTITY\|FUNCTION\|PACKAGE\
          \( BODY\)?\|PROCEDURE\|PROCESS\|TYPE\)[ \t]+\([^ \t(]+\)/\3/'

   * Tag Tcl files (this last example shows the usage of a NAMEREGEXP):

          --lang=none --regex='/proc[ \t]+\([^ \t]+\)/\1/'

   For a list of the other available `etags' options, execute `etags
--help'.


File: emacs,  Node: Select Tags Table,  Next: Find Tag,  Prev: Create Tags Table,  Up: Tags

Selecting a Tags Table
----------------------

   Emacs has at any time one "selected" tags table, and all the commands
for working with tags tables use the selected one.  To select a tags
table, type `M-x visit-tags-table', which reads the tags table file
name as an argument.  The name `TAGS' in the default directory is used
as the default file name.

   All this command does is store the file name in the variable
`tags-file-name'.  Emacs does not actually read in the tags table
contents until you try to use them.  Setting this variable yourself is
just as good as using `visit-tags-table'.  The variable's initial value
is `nil'; that value tells all the commands for working with tags tables
that they must ask for a tags table file name to use.

   Using `visit-tags-table' when a tags table is already loaded gives
you a choice: you can add the new tags table to the current list of
tags tables, or start a new list.  The tags commands use all the tags
tables in the current list.  If you start a new list, the new tags table
is used _instead_ of others.  If you add the new table to the current
list, it is used _as well as_ the others.  When the tags commands scan
the list of tags tables, they don't always start at the beginning of
the list; they start with the first tags table (if any) that describes
the current file, proceed from there to the end of the list, and then
scan from the beginning of the list until they have covered all the
tables in the list.

   You can specify a precise list of tags tables by setting the variable
`tags-table-list' to a list of strings, like this:

     (setq tags-table-list
           '("~/emacs" "/usr/local/lib/emacs/src"))

This tells the tags commands to look at the `TAGS' files in your
`~/emacs' directory and in the `/usr/local/lib/emacs/src' directory.
The order depends on which file you are in and which tags table
mentions that file, as explained above.

   Do not set both `tags-file-name' and `tags-table-list'.


File: emacs,  Node: Find Tag,  Next: Tags Search,  Prev: Select Tags Table,  Up: Tags

Finding a Tag
-------------

   The most important thing that a tags table enables you to do is to
find the definition of a specific tag.

`M-. TAG <RET>'
     Find first definition of TAG (`find-tag').

`C-u M-.'
     Find next alternate definition of last tag specified.

`C-u - M-.'
     Go back to previous tag found.

`C-M-. PATTERN <RET>'
     Find a tag whose name matches PATTERN (`find-tag-regexp').

`C-u C-M-.'
     Find the next tag whose name matches the last pattern used.

`C-x 4 . TAG <RET>'
     Find first definition of TAG, but display it in another window
     (`find-tag-other-window').

`C-x 5 . TAG <RET>'
     Find first definition of TAG, and create a new frame to select the
     buffer (`find-tag-other-frame').

`M-*'
     Pop back to where you previously invoked `M-.' and friends.

   `M-.' (`find-tag') is the command to find the definition of a
specified tag.  It searches through the tags table for that tag, as a
string, and then uses the tags table info to determine the file that the
definition is in and the approximate character position in the file of
the definition.  Then `find-tag' visits that file, moves point to the
approximate character position, and searches ever-increasing distances
away to find the tag definition.

   If an empty argument is given (just type <RET>), the sexp in the
buffer before or around point is used as the TAG argument.  *Note
Lists::, for info on sexps.

   You don't need to give `M-.' the full name of the tag; a part will
do.  This is because `M-.' finds tags in the table which contain TAG as
a substring.  However, it prefers an exact match to a substring match.
To find other tags that match the same substring, give `find-tag' a
numeric argument, as in `C-u M-.'; this does not read a tag name, but
continues searching the tags table's text for another tag containing
the same substring last used.  If you have a real <META> key, `M-0 M-.'
is an easier alternative to `C-u M-.'.

   Like most commands that can switch buffers, `find-tag' has a variant
that displays the new buffer in another window, and one that makes a
new frame for it.  The former is `C-x 4 .', which invokes the command
`find-tag-other-window'.  The latter is `C-x 5 .', which invokes
`find-tag-other-frame'.

   To move back to places you've found tags recently, use `C-u - M-.';
more generally, `M-.' with a negative numeric argument.  This command
can take you to another buffer.  `C-x 4 .' with a negative argument
finds the previous tag location in another window.

   As well as going back to places you've found tags recently, you can
go back to places _from where_ you found them.  Use `M-*', which
invokes the command `pop-tag-mark', for this.  Typically you would find
and study the definition of something with `M-.' and then return to
where you were with `M-*'.

   Both `C-u - M-.' and `M-*' allow you to retrace your steps to a
depth determined by the variable `find-tag-marker-ring-length'.

   The command `C-M-.' (`find-tag-regexp') visits the tags that match a
specified regular expression.  It is just like `M-.' except that it
does regexp matching instead of substring matching.


File: emacs,  Node: Tags Search,  Next: List Tags,  Prev: Find Tag,  Up: Tags

Searching and Replacing with Tags Tables
----------------------------------------

   The commands in this section visit and search all the files listed
in the selected tags table, one by one.  For these commands, the tags
table serves only to specify a sequence of files to search.

`M-x tags-search <RET> REGEXP <RET>'
     Search for REGEXP through the files in the selected tags table.

`M-x tags-query-replace <RET> REGEXP <RET> REPLACEMENT <RET>'
     Perform a `query-replace-regexp' on each file in the selected tags
     table.

`M-,'
     Restart one of the commands above, from the current location of
     point (`tags-loop-continue').

   `M-x tags-search' reads a regexp using the minibuffer, then searches
for matches in all the files in the selected tags table, one file at a
time.  It displays the name of the file being searched so you can
follow its progress.  As soon as it finds an occurrence, `tags-search'
returns.

   Having found one match, you probably want to find all the rest.  To
find one more match, type `M-,' (`tags-loop-continue') to resume the
`tags-search'.  This searches the rest of the current buffer, followed
by the remaining files of the tags table.

   `M-x tags-query-replace' performs a single `query-replace-regexp'
through all the files in the tags table.  It reads a regexp to search
for and a string to replace with, just like ordinary `M-x
query-replace-regexp'.  It searches much like `M-x tags-search', but
repeatedly, processing matches according to your input.  *Note
Replace::, for more information on query replace.

   It is possible to get through all the files in the tags table with a
single invocation of `M-x tags-query-replace'.  But often it is useful
to exit temporarily, which you can do with any input event that has no
special query replace meaning.  You can resume the query replace
subsequently by typing `M-,'; this command resumes the last tags search
or replace command that you did.

   The commands in this section carry out much broader searches than the
`find-tag' family.  The `find-tag' commands search only for definitions
of tags that match your substring or regexp.  The commands
`tags-search' and `tags-query-replace' find every occurrence of the
regexp, as ordinary search commands and replace commands do in the
current buffer.

   These commands create buffers only temporarily for the files that
they have to search (those which are not already visited in Emacs
buffers).  Buffers in which no match is found are quickly killed; the
others continue to exist.

   It may have struck you that `tags-search' is a lot like `grep'.  You
can also run `grep' itself as an inferior of Emacs and have Emacs show
you the matching lines one by one.  This works much like running a
compilation; finding the source locations of the `grep' matches works
like finding the compilation errors.  *Note Compilation::.


File: emacs,  Node: List Tags,  Prev: Tags Search,  Up: Tags

Tags Table Inquiries
--------------------

`M-x list-tags <RET> FILE <RET>'
     Display a list of the tags defined in the program file FILE.

`M-x tags-apropos <RET> REGEXP <RET>'
     Display a list of all tags matching REGEXP.

   `M-x list-tags' reads the name of one of the files described by the
selected tags table, and displays a list of all the tags defined in
that file.  The "file name" argument is really just a string to compare
against the file names recorded in the tags table; it is read as a
string rather than as a file name.  Therefore, completion and
defaulting are not available, and you must enter the file name the same
way it appears in the tags table.  Do not include a directory as part of
the file name unless the file name recorded in the tags table includes a
directory.

   `M-x tags-apropos' is like `apropos' for tags (*note Apropos::).  It
reads a regexp, then finds all the tags in the selected tags table
whose entries match that regexp, and displays the tag names found.

   You can also perform completion in the buffer on the name space of
tag names in the current tags tables.  *Note Symbol Completion::.


File: emacs,  Node: Emerge,  Next: C Modes,  Prev: Tags,  Up: Programs

Merging Files with Emerge
=========================

   It's not unusual for programmers to get their signals crossed and
modify the same program in two different directions.  To recover from
this confusion, you need to merge the two versions.  Emerge makes this
easier.  See also *Note Comparing Files::, for commands to compare in a
more manual fashion, and *Note Emerge: (ediff)Emerge.

* Menu:

* Overview of Emerge::	How to start Emerge.  Basic concepts.
* Submodes of Emerge::	Fast mode vs. Edit mode.
			  Skip Prefers mode and Auto Advance mode.
* State of Difference::	You do the merge by specifying state A or B
			  for each difference.
* Merge Commands::	Commands for selecting a difference,
			  changing states of differences, etc.
* Exiting Emerge::	What to do when you've finished the merge.
* Combining in Emerge::	    How to keep both alternatives for a difference.
* Fine Points of Emerge::   Misc.


File: emacs,  Node: Overview of Emerge,  Next: Submodes of Emerge,  Up: Emerge

Overview of Emerge
------------------

   To start Emerge, run one of these four commands:

`M-x emerge-files'
     Merge two specified files.

`M-x emerge-files-with-ancestor'
     Merge two specified files, with reference to a common ancestor.

`M-x emerge-buffers'
     Merge two buffers.

`M-x emerge-buffers-with-ancestor'
     Merge two buffers with reference to a common ancestor in a third
     buffer.

   The Emerge commands compare two files or buffers, and display the
comparison in three buffers: one for each input text (the "A buffer"
and the "B buffer"), and one (the "merge buffer") where merging takes
place.  The merge buffer shows the full merged text, not just the
differences.  Wherever the two input texts differ, you can choose which
one of them to include in the merge buffer.

   The Emerge commands that take input from existing buffers use only
the accessible portions of those buffers, if they are narrowed (*note
Narrowing::).

   If a common ancestor version is available, from which the two texts
to be merged were both derived, Emerge can use it to guess which
alternative is right.  Wherever one current version agrees with the
ancestor, Emerge presumes that the other current version is a deliberate
change which should be kept in the merged version.  Use the
`with-ancestor' commands if you want to specify a common ancestor text.
These commands read three file or buffer names--variant A, variant B,
and the common ancestor.

   After the comparison is done and the buffers are prepared, the
interactive merging starts.  You control the merging by typing special
"merge commands" in the merge buffer.  The merge buffer shows you a
full merged text, not just differences.  For each run of differences
between the input texts, you can choose which one of them to keep, or
edit them both together.

   The merge buffer uses a special major mode, Emerge mode, with
commands for making these choices.  But you can also edit the buffer
with ordinary Emacs commands.

   At any given time, the attention of Emerge is focused on one
particular difference, called the "selected" difference.  This
difference is marked off in the three buffers like this:

     vvvvvvvvvvvvvvvvvvvv
     TEXT THAT DIFFERS
     ^^^^^^^^^^^^^^^^^^^^

Emerge numbers all the differences sequentially and the mode line
always shows the number of the selected difference.

   Normally, the merge buffer starts out with the A version of the text.
But when the A version of a difference agrees with the common ancestor,
then the B version is initially preferred for that difference.

   Emerge leaves the merged text in the merge buffer when you exit.  At
that point, you can save it in a file with `C-x C-w'.  If you give a
numeric argument to `emerge-files' or `emerge-files-with-ancestor', it
reads the name of the output file using the minibuffer.  (This is the
last file name those commands read.)  Then exiting from Emerge saves
the merged text in the output file.

   Normally, Emerge commands save the output buffer in its file when you
exit.  If you abort Emerge with `C-]', the Emerge command does not save
the output buffer, but you can save it yourself if you wish.


File: emacs,  Node: Submodes of Emerge,  Next: State of Difference,  Prev: Overview of Emerge,  Up: Emerge

Submodes of Emerge
------------------

   You can choose between two modes for giving merge commands: Fast mode
and Edit mode.  In Fast mode, basic merge commands are single
characters, but ordinary Emacs commands are disabled.  This is
convenient if you use only merge commands.  In Edit mode, all merge
commands start with the prefix key `C-c C-c', and the normal Emacs
commands are also available.  This allows editing the merge buffer, but
slows down Emerge operations.

   Use `e' to switch to Edit mode, and `C-c C-c f' to switch to Fast
mode.  The mode line indicates Edit and Fast modes with `E' and `F'.

   Emerge has two additional submodes that affect how particular merge
commands work: Auto Advance mode and Skip Prefers mode.

   If Auto Advance mode is in effect, the `a' and `b' commands advance
to the next difference.  This lets you go through the merge faster as
long as you simply choose one of the alternatives from the input.  The
mode line indicates Auto Advance mode with `A'.

   If Skip Prefers mode is in effect, the `n' and `p' commands skip
over differences in states prefer-A and prefer-B (*note State of
Difference::).  Thus you see only differences for which neither version
is presumed "correct."  The mode line indicates Skip Prefers mode with
`S'.

   Use the command `s a' (`emerge-auto-advance-mode') to set or clear
Auto Advance mode.  Use `s s' (`emerge-skip-prefers-mode') to set or
clear Skip Prefers mode.  These commands turn on the mode with a
positive argument, turns it off with a negative or zero argument, and
toggle the mode with no argument.

