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This chapter describes Emacs features for maintaining programs. The version control features (see section M.7 Version Control) are also particularly useful for this purpose.
W.1 Change Logs Maintaining a change history for your program. W.2 Tags Tables Go direct to any function in your program in one command. Tags remembers which file it is in. W.3 Merging Files with Emerge A convenient way of merging two versions of a program.
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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). If that file is actually
a backup file, it makes an entry appropriate for the file's
parent--that is useful for making log entries for functions that
have been deleted in the current version.
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.
You should put a copyright notice and permission notice at the end of the change log file. Here is an example:
Copyright 1997, 1998 Free Software Foundation, Inc. Copying and distribution of this file, with or without modification, are permitted provided the copyright notice and this notice are preserved. |
Of course, you should substitute the proper years and copyright holder.
A change log entry starts with a header line that contains the
current date, your name, and your email address (taken from the
variable user-mail-address). 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.
|
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.
When the option add-log-keep-changes-together is
non-nil, C-x 4 a adds to any existing entry for the file
rather than starting a new entry.
If the value of the variable change-log-version-info-enabled
is non-nil, C-x 4 a adds the file's version number to the
change log entry. It finds the version number by searching the first
ten percent of the file, using regular expressions from the variable
change-log-version-number-regexp-list.
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.
You can use the command M-x change-log-merge to merge other log files into a buffer in Change Log Mode, preserving the date ordering of entries.
Versions of Emacs before 20.1 used a different format for the time of the change log entry:
Fri May 25 11:23:23 1993 Richard Stallman <rms@gnu.org> |
The M-x change-log-redate command converts all the old-style date entries in the change log file visited in the current buffer to the new format, to make the file uniform in style. This is handy when entries are contributed by many different people, some of whom use old versions of Emacs.
Version control systems are another way to keep track of changes in your program and keep a change log. See section M.7.3.4 Features of the Log Entry Buffer.
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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 file names, functions and subroutines, and may also include global variables, data types, and anything else convenient. Each name recorded is called a tag.
See also the Ebrowse facility, which is tailored for C++. See section `Ebrowse' in Ebrowse User's Manual.
W.2.1 Source File Tag Syntax Tag syntax for various types of code and text files. W.2.2 Creating Tags Tables Creating a tags table with etags.W.2.3 Etags Regexps Create arbitrary tags using regular expressions. W.2.4 Selecting a Tags Table How to visit a tags table. W.2.5 Finding a Tag Commands to find the definition of a specific tag. W.2.6 Searching and Replacing with Tags Tables Using a tags table for searching and replacing. W.2.7 Tags Table Inquiries Listing and finding tags defined in a file.
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Here is how tag syntax is defined for the most popular languages:
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.
You can tag function declarations and external variables in addition
to function definitions by giving the `--declarations' option to
etags.
operator definitions have
tag names like `operator+'.
interface, extends and implements constructs.
Tags for variables and functions in classes are named
`class.variable' and `class.function'.
\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.
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.
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 Ada, the same name can be used for different kinds of entity (e.g., for a procedure and for a function). Also, for things like packages, procedures and functions, there is the spec (i.e. the interface) and the body (i.e. the implementation). To make it easier to pick the definition you want, Ada tag name have suffixes indicating the type of entity:
Thus, M-x find-tag RET bidule/b RET will go
directly to the body of the package bidule, while M-x
find-tag RET bidule RET will just search for any tag
bidule.
sub,
my and local keywords. Use `--globals' if you want
to tag global variables.
def or class at the beginning of a line
generate a tag.
You can also generate tags based on regexp matching (see section W.2.3 Etags Regexps) to handle other formats and languages.
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The etags program is used to create a tags table file. It knows
the syntax of several languages, as described in
W.2.1 Source File 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.
If the specified files don't exist, etags looks for
compressed versions of them and uncompresses them to read them. Under
MS-DOS, etags also looks for file names like `mycode.cgz'
if it is given `mycode.c' on the command line and `mycode.c'
does not exist.
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. If the tags table fails to record a tag, or records it for the wrong file, then Emacs cannot possibly find its definition until you update the tags table. However, if the position recorded in the tags table becomes a little bit wrong (due to other editing), the only consequence is a slight delay in finding the tag. Even if the stored position is very far wrong, Emacs will still find the tag, after searching most of the file for it. Even that delay is hardly noticeable with today's computers.
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 virtually 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 covered all the source 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
(see section W.2.3 Etags Regexps).
`etags --help' prints the list of the languages etags
knows, and the file name rules for guessing the language. It also prints
a list of all the available etags options, together with a short
explanation.
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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 (as will usually be the case), you should add a nameregexp, to pick out just the tag. This will enable Emacs to find tags more accurately and to do completion on tag names more reliably. You can find some examples below.
The option `--ignore-case-regex' (or `-c') works like `--regex', except that matching ignores case. This is appropriate for certain programming languages.
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'.
You can specify a regular expression for a particular language, by
writing `{lang}' in front of it. Then etags will use
the regular expression only for files of that language. (`etags
--help' prints the list of languages recognized by etags.) The
following example tags the DEFVAR macros in the Emacs source
files, for the C language only:
--regex='{c}/[ \t]*DEFVAR_[A-Z_ \t(]+"\([^"]+\)"/'
|
This feature is particularly useful when you store a list of regular
expressions in a file. The following option syntax instructs
etags to read two files of regular expressions. The regular
expressions contained in the second file are matched without regard to
case.
--regex=@first-file --ignore-case-regex=@second-file |
A regex file contains one regular expressions per line. Empty lines,
and lines beginning with space or tab are ignored. When the first
character in a line is `@', etags assumes that the rest
of the line is the name of a file of regular expressions; thus, one
such file can include another file. All the other lines are taken to
be regular expressions. If the first non-whitespace text on the line
is `--', that line is a comment.
For example, one can create a file called `emacs.tags' with the following contents:
-- This is for GNU Emacs C source files
{c}/[ \t]*DEFVAR_[A-Z_ \t(]+"\([^"]+\)"/\1/
|
and then use it like this:
etags --regex=@emacs.tags *.[ch] */*.[ch] |
Here are some more examples. The regexps are quoted to protect them from shell interpretation.
etags --language=none \
--regex='/[ \t]*function.*=[ \t]*\([^ \t]*\)[ \t]*(/\1/' \
--regex='/###key \(.*\)/\1/' \
--regex='/[ \t]*global[ \t].*/' \
*.m
|
Note that tags are not generated for scripts, so that you have to add a line by yourself of the form `###key scriptname' if you want to jump to it.
etags --language=none --regex='/proc[ \t]+\([^ \t]+\)/\1/' *.tcl |
etags --language=none \ --regex='/[ \t]*\(ARCHITECTURE\|CONFIGURATION\) +[^ ]* +OF/' \ --regex='/[ \t]*\(ATTRIBUTE\|ENTITY\|FUNCTION\|PACKAGE\ \( BODY\)?\|PROCEDURE\|PROCESS\|TYPE\)[ \t]+\([^ \t(]+\)/\3/' |
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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.
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The most important thing that a tags table enables you to do is to find the definition of a specific tag.
find-tag).
find-tag-regexp).
find-tag-other-window).
find-tag-other-frame).
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 balanced expression in the buffer before or around point is used as the tag argument. See section U.4.1 Expressions with Balanced Parentheses.
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.
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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.
query-replace-regexp on each file in the selected tags table.
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. See section K.7 Replacement Commands, for more information on query replace.
You can control the case-sensitivity of tags search commands by
customizing the value of the variable tags-case-fold-search. The
default is to use the same setting as the value of
case-fold-search (see section K.6 Searching and Case).
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.
See section V.1 Running Compilations under Emacs.
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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
(see section G.4 Apropos). It finds all the tags in the selected tags table
whose entries match regexp, and displays them. If the variable
tags-apropos-verbose is non-nil, it displays the names
of the tags files together with the tag names.
You can customize the appearance of the output with the face
tags-tag-face. You can display additional output with M-x
tags-apropos by customizing the variable
tags-apropos-additional-actions---see its documentation for
details.
You can also use the collection of tag names to complete a symbol name in the buffer. See section U.8 Completion for Symbol Names.
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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 M.9 Comparing Files, for commands to compare in a more manual fashion, and section `Top' in The Ediff Manual.
W.3.1 Overview of Emerge How to start Emerge. Basic concepts. W.3.2 Submodes of Emerge Fast mode vs. Edit mode. Skip Prefers mode and Auto Advance mode. W.3.3 State of a Difference You do the merge by specifying state A or B for each difference. W.3.4 Merge Commands Commands for selecting a difference, changing states of differences, etc. W.3.5 Exiting Emerge What to do when you've finished the merge. W.3.6 Combining the Two Versions How to keep both alternatives for a difference. W.3.7 Fine Points of Emerge Misc.
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To start Emerge, run one of these four commands:
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 (see section AC.22 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.
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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 (see section W.3.3 State of a 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.
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In the merge buffer, a difference is marked with lines of `v' and `^' characters. Each difference has one of these seven states:
When you select a difference, its state changes from default-A or default-B to plain A or B. Thus, the selected difference never has state default-A or default-B, and these states are never displayed in the mode line.
The command d a chooses default-A as the default state, and d b chooses default-B. This chosen default applies to all differences which you haven't ever selected and for which no alternative is preferred. If you are moving through the merge sequentially, the differences you haven't selected are those following the selected one. Thus, while moving sequentially, you can effectively make the A version the default for some sections of the merge buffer and the B version the default for others by using d a and d b between sections.
These two states are displayed in the mode line as `A*' and `B*'.
Once a difference is in this state, the a and b commands don't do anything to it unless you give them a numeric argument.
The mode line displays this state as `comb'.
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Here are the Merge commands for Fast mode; in Edit mode, precede them with C-c C-c:
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The q command (emerge-quit) finishes the merge, storing
the results into the output file if you specified one. It restores the
A and B buffers to their proper contents, or kills them if they were
created by Emerge and you haven't changed them. It also disables the
Emerge commands in the merge buffer, since executing them later could
damage the contents of the various buffers.
C-] aborts the merge. This means exiting without writing the output file. If you didn't specify an output file, then there is no real difference between aborting and finishing the merge.
If the Emerge command was called from another Lisp program, then its
return value is t for successful completion, or nil if you
abort.
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Sometimes you want to keep both alternatives for a particular difference. To do this, use x c, which edits the merge buffer like this:
#ifdef NEW version from A buffer #else /* not NEW */ version from B buffer #endif /* not NEW */ |
While this example shows C preprocessor conditionals delimiting the two
alternative versions, you can specify the strings to use by setting
the variable emerge-combine-versions-template to a string of your
choice. In the string, `%a' says where to put version A, and
`%b' says where to put version B. The default setting, which
produces the results shown above, looks like this:
"#ifdef NEW\n%a#else /* not NEW */\n%b#endif /* not NEW */\n" |
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During the merge, you mustn't try to edit the A and B buffers yourself. Emerge modifies them temporarily, but ultimately puts them back the way they were.
You can have any number of merges going at once--just don't use any one buffer as input to more than one merge at once, since the temporary changes made in these buffers would get in each other's way.
Starting Emerge can take a long time because it needs to compare the
files fully. Emacs can't do anything else until diff finishes.
Perhaps in the future someone will change Emerge to do the comparison in
the background when the input files are large--then you could keep on
doing other things with Emacs until Emerge is ready to accept
commands.
After setting up the merge, Emerge runs the hook
emerge-startup-hook (see section AD.2.3 Hooks).
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