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Emacs has many commands designed to understand the syntax of
programming languages such as Lisp and C. These commands can
The commands for words, sentences
and paragraphs are very useful in editing code even though their
canonical application is for editing human language text. Most symbols contain words
(see section Words); sentences can be found in
strings and comments (see section Sentences).
Paragraphs per se don't exist in code, but the paragraph commands are useful
anyway, because programming language major modes define
paragraphs to begin and end at blank lines (see section Paragraphs). Judicious use of
blank lines to make the program clearer will also provide useful
chunks of text for the paragraph commands to work on.
The selective display feature is useful for looking at the
overall structure of a function (see section Selective Display). This feature
causes only the lines that are indented less than a specified
amount to appear on the screen.
- Program Modes: Major
modes for editing programs.
- Lists: Expressions with
balanced parentheses.
- List Commands: The
commands for working with list and sexps.
- Defuns: Each program is
made up of separate functions. There are editing commands
to operate on them.
- Program Indent:
Adjusting indentation to show the nesting.
- Matching: Insertion of
a close-delimiter flashes matching open.
- Comments: Inserting,
killing, and aligning comments.
- Balanced Editing:
Inserting two matching parentheses at once, etc.
- Symbol Completion:
Completion on symbol names of your program or language.
- Documentation: Getting
documentation of functions you plan to call.
- Change Log: Maintaining
a change history for your program.
- Tags: Go direct to any
function in your program in one command. Tags remembers
which file it is in.
- Emerge: A convenient
way of merging two versions of a program.
- C Mode: Special
commands of C mode (and C++ mode).
- Fortran: Fortran mode
and its special features.
- Asm Mode: Asm mode and
its special features.
Emacs also has major modes for the programming languages Lisp,
Scheme (a variant of Lisp), Awk, C, C++, Fortran, Icon, Pascal,
Perl and Tcl. There is also a major mode for makefiles, called
Makefile mode.
Ideally, a major mode should be implemented for each
programming language that you might want to edit with Emacs; but
often the mode for one language can serve for other syntactically
similar languages. The language modes that exist are those that
someone decided to take the trouble to write.
There are several forms of Lisp mode, which differ in the way
they interface to Lisp execution. See section Executing Lisp Expressions.
Each of the programming language modes defines the TAB
key to run an indentation
function that knows the indentation
conventions of that language and updates the current line's indentation accordingly. For
example, in C mode TAB is bound to c-indent-line. LFD
is normally defined to do RET followed by TAB;
thus, it too indents in a mode-specific fashion.
In most programming languages, indentation
is likely to vary from line to line. So the major modes for those
languages rebind DEL to treat a tab as if it were the
equivalent number of spaces (using the command backward-delete-char-untabify).
This makes it possible to rub out indentation
one column at a time without worrying whether it is made up of
spaces or tabs. Use C-b C-d to delete a tab character before point, in these modes.
Programming language modes define paragraphs to be separated
only by blank lines, so that the paragraph
commands remain useful. Auto Fill mode, if enabled in a
programming language major mode, indents the new lines which it
creates.
Turning on a major mode runs a normal hook called the mode
hook, which is the value of a Lisp variable. Each major mode has a
mode hook, and the hook's name is always made from the mode command's name by adding -hook.
For example, turning on C mode runs the hook c-mode-hook,
while turning on Lisp mode runs the hook lisp-mode-hook.
See section Hooks.
By convention, Emacs keys for dealing with balanced
expressions are usually Control-Meta
characters. They tend to be analogous in function to their
Control and Meta equivalents.
These commands are usually thought of as pertaining to
expressions in programming languages, but can be useful with any
language in which some sort of parentheses exist (including human
languages).
These commands fall into two classes. Some deal only with lists
(parenthetical groupings). They see nothing except parentheses,
brackets, braces (whichever ones must balance in the language you
are working with), and escape characters that might be used to
quote those.
The other commands deal with expressions or sexps.
The word `sexp' is derived
from s-expression, the ancient term for an expression
in Lisp. But in Emacs, the notion of `sexp' is not limited to Lisp. It
refers to an expression in whatever language your program is
written in. Each programming language has its own major mode,
which customizes the syntax tables so that expressions in that
language count as sexps.
Sexps typically include symbols, numbers, and string constants, as well as
anything contained in parentheses, brackets or braces.
In languages that use prefix and infix operators, such as C,
it is not possible for all expressions to be sexps. For example,
C mode does not recognize foo + bar as a sexp, even though it is
a C expression; it recognizes foo as one sexp and bar as
another, with the + as punctuation between them.
This is a fundamental ambiguity: both foo + bar and foo
are legitimate choices for the sexp
to move over if point is at
the f. Note that (foo + bar) is a
single sexp in C mode.
Some languages have obscure forms of expression syntax that
nobody has bothered to make Emacs understand properly.
- C-M-f Move forward over a sexp (
forward-sexp). C-M-b
Move backward over a sexp
(backward-sexp). C-M-k
Kill sexp forward (kill-sexp). C-M-DEL
Kill sexp backward (backward-kill-sexp). C-M-u
Move up and backward in list
structure (backward-up-list). C-M-d
Move down and forward in list
structure (down-list). C-M-n
Move forward over a list
(forward-list). C-M-p
Move backward over a list
(backward-list). C-M-t
Transpose expressions (transpose-sexps). C-M-@
Put mark after
following expression (mark-sexp).
To move forward over a sexp,
use C-M-f (forward-sexp). If the first
significant character after point is an opening delimiter ((
in Lisp; (, [ or { in C), C-M-f
moves past the matching closing delimiter. If the character begins a symbol, string, or number, C-M-f
moves over that.
The command C-M-b
(backward-sexp)
moves backward over a sexp.
The detailed rules are like those above for C-M-f, but
with directions reversed. If there are any prefix characters
(single-quote, backquote and comma, in Lisp) preceding the sexp, C-M-b moves
back over them as well. The sexp
commands move across comments as if they were whitespace in most modes.
C-M-f or C-M-b with an argument repeats
that operation the specified number of times; with a negative
argument, it moves in the opposite direction.
Killing a sexp at a time can be done with C-M-k
(kill-sexp)
or C-M-DEL (backward-kill-sexp). C-M-k
kills the characters that C-M-f would move over, and C-M-DEL
kills the characters that C-M-b would move over.
The list
commands move over lists like the sexp commands but skip blithely
over any number of other kinds of sexps (symbols, strings, etc).
They are C-M-n (forward-list) and C-M-p
(backward-list).
The main reason they are useful is that they usually ignore
comments (since the comments usually do not contain any lists).
C-M-n and C-M-p stay at the same level
in parentheses, when that's possible. To move up one (or n)
levels, use C-M-u (backward-up-list). C-M-u
moves backward up past one unmatched opening delimiter. A
positive argument serves as a repeat count; a negative argument
reverses direction of motion and also requests repetition, so it
moves forward and up one or more levels.
To move down in list
structure, use C-M-d (down-list). In Lisp mode,
where ( is the only opening delimiter, this is
nearly the same as searching
for a (. An argument specifies the number of levels
of parentheses to go down.
A somewhat random-sounding command
which is nevertheless handy is C-M-t (transpose-sexps),
which drags the previous sexp
across the next one. An argument serves as a repeat count, and a
negative argument drags backwards (thus canceling out the effect
of C-M-t with a positive argument). An argument of
zero, rather than doing nothing, transposes the sexps ending
after point and the mark.
To set the region around
the next sexp in the buffer, use C-M-@ (mark-sexp), which sets mark at the same place that C-M-f
would move to. C-M-@ takes arguments like C-M-f.
In particular, a negative argument is useful for putting the mark at the beginning of the
previous sexp.
The list and sexp commands' understanding of
syntax is completely controlled by the syntax table. Any character can, for example, be
declared to be an opening delimiter and act like an open
parenthesis. See section The Syntax
Table.
In Emacs, a parenthetical grouping at the top level in the buffer is called a defun. The name
derives from the fact that most top-level lists in a Lisp file
are instances of the special form defun,
but any top-level parenthetical grouping counts as a defun in Emacs parlance
regardless of what its contents are, and regardless of the
programming language in use. For example, in C, the body of a
function definition is a defun.
- C-M-a Move to beginning of current or preceding defun (
beginning-of-defun). C-M-e
Move to end of current or following defun (end-of-defun). C-M-h
Put region around
whole current or following defun
(mark-defun).
The commands to move to the beginning and end of the current defun are C-M-a (beginning-of-defun) and C-M-e
(end-of-defun).
If you wish to operate on the current defun, use C-M-h (mark-defun) which puts point at the beginning and mark at the end of the current or
next defun. For example, this
is the easiest way to get ready to move the defun to a different place in the text. In C mode, C-M-h
runs the function mark-c-function,
which is almost the same as mark-defun; the
difference is that it backs up over the argument declarations,
function name and returned data type so that the entire C
function is inside the region.
See section Commands to Mark Textual
Objects.
Emacs assumes that any open-parenthesis found in the leftmost
column is the start of a defun.
Therefore, never put an open-parenthesis at the left
margin in a Lisp file unless it is the start of a top level list.
Never put an open-brace or other opening delimiter at the
beginning of a line of C code unless it starts the body of a
function. The most likely problem case is when you want
an opening delimiter at the start of a line inside a string. To avoid trouble, put an
escape character (\,
in C and Emacs Lisp, / in some other Lisp dialects)
before the opening delimiter. It will not affect the contents of
the string.
In the remotest past, the original Emacs found defuns by
moving upward a level of parentheses until there were no more
levels to go up. This always required scanning all the way back
to the beginning of the buffer,
even for a small function. To speed up the operation, Emacs was
changed to assume that any ( (or other character assigned the syntactic
class of opening-delimiter) at the left margin is the start of a defun. This heuristic is nearly
always right and avoids the costly scan; however, it mandates the
convention described above.
The best way to keep a program properly indented is to use
Emacs to re-indent it as you change it. Emacs has commands to
indent properly either a single line, a specified number of
lines, or all of the lines inside a single parenthetical
grouping.
Emacs also provides a Lisp pretty-printer in the library pp.
This program prints a Lisp object with indentation chosen to look nice.
- TAB Adjust indentation of current
line. LFD Equivalent to RET
followed by TAB (
newline-and-indent).
The basic indentation command is TAB, which
gives the current line the correct indentation
as determined from the previous lines. The function that TAB
runs depends on the major mode; it is lisp-indent-line
in Lisp mode, c-indent-line in C mode, etc. These
functions understand different syntaxes for different languages,
but they all do about the same thing. TAB in any
programming language major mode inserts or deletes whitespace at the beginning of
the current line, independent of where point is in the line. If point is inside the whitespace at the beginning of
the line, TAB leaves it at the end of that whitespace; otherwise, TAB
leaves point fixed with
respect to the characters around it.
Use C-q TAB to insert a tab at point.
When entering lines of new code, use LFD (newline-and-indent),
which is equivalent to a RET followed by a TAB. LFD
creates a blank line, and then gives it the appropriate indentation.
TAB indents the second and following lines of the
body of a parenthetical grouping each under the preceding one;
therefore, if you alter one line's indentation
to be nonstandard, the lines below will tend to follow it. This
behavior is convenient in cases where you have overridden the
standard result of TAB because you find it unaesthetic
for a particular line.
Remember that an open-parenthesis, open-brace or other opening
delimiter at the left margin is assumed by Emacs (including the indentation routines) to be the
start of a function. Therefore, you must never have an opening
delimiter in column zero that is not the beginning of a function,
not even inside a string.
This restriction is vital for
making the indentation
commands fast; you must simply accept it. See section Defuns, for more information on
this.
When you wish to re-indent several lines of code which have
been altered or moved to a different level in the list structure, you have several
commands available.
- C-M-q Re-indent all the lines within one list (
indent-sexp). C-u TAB
Shift an entire list
rigidly sideways so that its first line is properly
indented. C-M-\ Re-indent all lines in the region (indent-region).
You can re-indent the contents of a single list by positioning point before the beginning of it
and typing C-M-q (indent-sexp in Lisp mode, indent-c-exp
in C mode; also bound to other suitable commands in other modes).
The indentation of the line
the sexp starts on is not
changed; therefore, only the relative indentation within the list, and not its position, is
changed. To correct the position as well, type a TAB
before the C-M-q.
If the relative indentation
within a list is correct but
the indentation of its first
line is not, go to that line and type C-u TAB. TAB
with a numeric argument reindents the current line as usual, then
reindents by the same amount all the lines in the grouping
starting on the current line. In other words, it reindents the
whole grouping rigidly as a unit. It is clever, though, and does
not alter lines that start inside strings, or C preprocessor
lines when in C mode.
Another way to specify the range to be re-indented is with the region. The command C-M-\ (indent-region) applies TAB
to every line whose first character
is between point and mark.
The indentation pattern for
a Lisp expression can depend on the function called by the
expression. For each Lisp function, you can choose among several
predefined patterns of indentation,
or define an arbitrary one with a Lisp program.
The standard pattern of indentation
is as follows: the second line of the expression is indented
under the first argument, if that is on the same line as the
beginning of the expression; otherwise, the second line is
indented underneath the function name. Each following line is
indented under the previous line whose nesting depth is the same.
If the variable lisp-indent-offset
is non-nil, it overrides the usual indentation pattern for the
second line of an expression, so that such lines are always
indented lisp-indent-offset more columns than the
containing list.
The standard pattern is overridden for certain functions.
Functions whose names start with def always indent
the second line by lisp-body-indent extra columns
beyond the open-parenthesis starting the expression.
The standard pattern can be overridden in various ways for
individual functions, according to the lisp-indent-function
property of the function name. There are four possibilities for
this property:
nil This is the same as no property;
the standard indentation
pattern is used. defun
The pattern used for function names that start with def
is used for this function also. a number, number
The first number arguments of the function are distinguished
arguments; the rest are considered the body of
the expression. A line in the expression is indented
according to whether the first argument on it is
distinguished or not. If the argument is part of the
body, the line is indented lisp-body-indent
more columns than the open-parenthesis starting the
containing expression. If the argument is distinguished
and is either the first or second argument, it is
indented twice that many extra columns. If the
argument is distinguished and not the first or second
argument, the standard pattern is followed for that line. a
symbol, symbol symbol
should be a function name; that function is called to
calculate the indentation
of a line within this expression. The function receives
two arguments: -
- state The value returned by
parse-partial-sexp
(a Lisp primitive for indentation and
nesting computation) when it parses up to the
beginning of this line. pos The
position at which the line being indented begins.
It should return either a number, which is the number of
columns of indentation
for that line, or a list
whose car is such a number. The difference between
returning a number and returning a list is that a number
says that all following lines at the same nesting level
should be indented just like this one; a list says that following
lines might call for different indentations. This makes a
difference when the indentation
is being computed by C-M-q; if the value is a
number, C-M-q need not recalculate indentation for the
following lines until the end of the list.
Two variables control which commands perform C indentation and when.
If c-auto-newline
is non-nil, newlines are inserted both before and
after braces that you insert, and after colons and semicolons.
Correct C indentation is done
on all the lines that are made this way.
If c-tab-always-indent is nil, the TAB command in C mode does indentation only if point is at the left margin or
within the line's indentation.
If there is non-whitespace to
the left of point, then TAB
just inserts a tab character
in the buffer. Normally, this variable is t, and TAB
always reindents the current line. The default behavior means
that to insert a real tab character
you must quote it by typing C-q TAB.
C does not have anything analogous to particular function
names for which special forms of indentation
are desirable. However, it has a different need for customization facilities: many
different styles of C indentation
are in common use.
There are six variables you can set to control the style that
Emacs C mode uses.
- c-indent-level Indentation
of C statements within surrounding block. The surrounding
block's indentation is
the indentation of the
line on which the open-brace appears. c-continued-statement-offset
Extra indentation
given to a substatement, such as the then-clause of an if
or body of a while. c-brace-offset Extra indentation for line if
it starts with an open brace. c-brace-imaginary-offset
An open brace following other text is treated as if it
were this far to the right of the start of its line. c-argdecl-indent Indentation level of
declarations of C function arguments. c-label-offset
Extra indentation for
line that is a label, or case or default.
The variable c-indent-level
controls the indentation for C
statements with respect to the surrounding block. In the example
{
foo ();
the difference in indentation
between the lines is c-indent-level. Its standard
value is 2.
If the open-brace beginning the compound statement is not at
the beginning of its line, the c-indent-level is
added to the indentation of
the line, not the column of the open-brace. For example,
if (losing) {
do_this ();
One popular indentation
style is that which results from setting c-indent-level
to 8 and putting open-braces at the end of a line in this way. I
prefer to put the open-brace on a separate line.
In fact, the value of the variable c-brace-imaginary-offset
is also added to the indentation
of such a statement. Normally this variable is zero. Think of this variable as the imaginary
position of the open brace, relative to the first nonblank character on the line. By setting
this variable to 4 and c-indent-level
to 0, you can get this style:
if (x == y) {
do_it ();
}
When c-indent-level is zero, the statements
inside most braces will line up right under the open brace. But
there is an exception made for braces in column zero, such as
surrounding a function's body. The statements just inside it do
not go at column zero. Instead, c-brace-offset and c-continued-statement-offset
(see below) are added to produce a typical offset between brace
levels, and the statements are indented that far.
c-continued-statement-offset controls the extra indentation for a line that
starts within a statement (but not within parentheses or
brackets). These lines are usually statements that are within
other statements, such as the then-clauses of if
statements and the bodies of while statements. This
parameter is the difference in indentation
between the two lines in
if (x == y)
do_it ();
Its standard value is 2. Some popular indentation styles correspond to
a value of zero for c-continued-statement-offset.
c-brace-offset is the extra indentation given to a line that
starts with an open-brace. Its standard value is zero; compare
if (x == y)
{
with
if (x == y)
do_it ();
if c-brace-offset were set to 4, the first
example would become
if (x == y)
{
c-argdecl-indent controls the indentation of declarations of
the arguments of a C function. It is absolute: argument
declarations receive exactly c-argdecl-indent
spaces. The standard value is 5, resulting in code like this:
char *
index (string, c)
char *string;
int c;
c-label-offset is the extra indentation given to a line that
contains a label, a case statement, or a default:
statement. Its standard value is -2, resulting in code like this
switch (c)
{
case 'x':
If c-label-offset were zero, the same code would
be indented as
switch (c)
{
case 'x':
This example assumes that the other variables above also have
their standard values.
I strongly recommend that you try out the indentation style produced by the
standard settings of these variables, together with putting open
braces on separate lines. You can see how it looks in all the C
source files of GNU Emacs.
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. See section The Syntax Table.
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 kind of
automatic parenthesis matching by loading the paren
library. To load it, type M-x load-library RET paren RET.
This library turns off the usual kind of matching parenthesis
display and substitutes another: 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.)
Because comments are such an important part of programming,
Emacs provides special commands for editing and inserting
comments.
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). M-LFD
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 re-indents 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.
If you are typing a comment
and wish to continue it on another line, you can use the command M-LFD (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 M-LFD 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 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.
See section Local Variables.
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. See section Syntax of Regular Expressions.)
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 M-LFD (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.
- M-( Put parentheses around next sexp(s) (
insert-parentheses). M-)
Move past next close parenthesis and re-indent (move-over-close-and-reindent).
The commands M-( (insert-parentheses)
and M-) (move-over-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 (in this
example there is none), and indenting with LFD 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-dont-require-spaces
to a non-nil value if you wish to inhibit this.
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.
There are two ways of determining the set of legitimate symbol
names to complete against. In most major modes, this uses a tags
table (see section Tags Tables);
the legitimate symbol names are the tag names listed in the tags
table file. The command which
implements this is complete-tag.
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. See section Checking and Correcting Spelling.
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.
Documentation on operating system commands, library functions
and system calls can be obtained with the M-x manual-entry command. This reads a topic as an
argument, and displays the ``man page''
on that topic. manual-entry starts a background
process that formats the manual page,
by running the man program. 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 you are using X Windows. 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. See
section Other Help Commands.
Since this process is only partially completed, it is still
useful to read manual pages.
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, each with two items:
Wed May 5 14:11:45 1993 Richard Stallman
* man.el: Rename symbols `man-*' to `Man-*'. (manual-entry):
Make prompt string clearer.
* simple.el (blink-matching-paren-distance): Change default to
12,000.
Tue May 4 12:42:19 1993 Richard Stallman
* 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.
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. LFD 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 keep track of changes
in your program and keep a change log. See section Log Entries.
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.
- 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.
- In C code, any C function or typedef is a tag, and so are
definitions of struct, union and enum. Any
#define
is also a tag, unless --no-defines is
specified when the tags table is constructed, which
sometimes makes the tags file much smaller. In C++ code,
member functions are also recognized.
- In Yacc or Bison 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 Fortran code, functions and subroutines are tags.
- In Pascal code, the tags are the functions and procedures
defined in the file.
- In Prolog code, a tag name appears at the left margin.
- In assembler code, labels appearing at the beginning of a
line, followed by a colon, are tags.
- In LaTeX text, the
argument of any of the commands
\chapter, \section, \subsection, \subsubsection, \eqno, \label, \ref, \cite, \bibitem
and \typeout is a tag.
- You can also generate tags based on regexp matching (see
section Creating Tags
Tables) for any text
file.
The etags program is used to create a tags table
file. It knows the syntax of several languages, as described in
section 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. 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.
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.
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 Cobol files (every label starting in column seven):
--language=none --regex='/.......[a-zA-Z0-9-]+\./'
Tag Postscript files (every label starting in column one):
--language=none --regex='#/[^ \t{]+#/'
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.
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.
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-. (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. See section Lists and
Sexps, 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.
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.
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. See section Replacement Commands, 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. See section Running Compilations under Emacs.
If you wish to process all the files in the selected tags
table, but not in the specific ways that M-x tags-search
and M-x tags-query-replace do, you can use M-x
next-file to visit the files one by one.
- C-u M-x next-file Visit the first file in the tags
table, and prepare to advance sequentially by files. M-x
next-file Visit the next file in the selected tags
table.
- 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 (see section 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. See section Completion for Symbol Names.
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 section Comparing Files.
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 (see section 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.
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 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.
In the merge buffer, a
difference is marked with lines of v and ^
characters. Each difference has one of these seven states:
- A The difference is showing the A version. The a command always produces
this state; the mode line indicates it with A.
-
B The difference is showing the B version. The b command always produces
this state; the mode line indicates it with B.
default-A default-B The difference is
showing the A or the B state by default, because you
haven't made a choice. All differences start in the
default-A state (and thus the merge buffer is a copy of the A buffer), except those for
which one alternative is ``preferred'' (see below).
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.
prefer-A prefer-B The difference is
showing the A or B state because it is preferred.
This means that you haven't made an explicit choice, but
one alternative seems likely to be right because the
other alternative agrees with the common ancestor. Thus,
where the A buffer
agrees with the common ancestor, the B version is
preferred, because chances are it is the one that was
actually changed.
These two states are displayed in the mode line as A*
and B*.
combined The difference is showing a
combination of the A and B states, as a result of the x
c or x C commands.
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.
Here are the Merge commands for Fast mode; in Edit mode,
precede them with C-c C-c:
- p Select the previous difference.
-
n Select the next difference.
a Choose the A version of this difference.
b Choose the B version of this difference.
C-u n j Select
difference number n.
. Select the difference containing point. You can use this command in the merge buffer or in the A or B buffer.
q Quit---finish the merge.
C-] Abort---exit merging and do not save the
output.
f Go into Fast mode. (In Edit mode, this is
actually C-c C-c f.)
e Go into Edit mode.
l Recenter (like C-l) all three
windows.
- Specify part of a prefix numeric argument.
digit Also specify part of a prefix
numeric argument.
d a Choose the A version as the default from
here down in the merge buffer.
d b Choose the B version as the default from
here down in the merge buffer.
c a Copy the A version of this difference into
the kill ring.
c b Copy the B version of this difference into
the kill ring.
i a Insert the A version of this difference at point.
i b Insert the B version of this difference at point.
m Put point
and mark around the
difference.
^ Scroll all three windows down (like M-v).
v Scroll all three windows up (like C-v).
Scroll all three windows left (like C-x
).
> Scroll all three windows
right (like C-x >).
| Reset horizontal scroll on all three windows.
x 1 Shrink the merge window to one line. (Use C-u
l to restore it to full size.)
x c Combine the two versions of this difference
(see section Combining the
Two Versions).
x f Show the names of the files/buffers Emerge
is operating on, in a Help window. (Use C-u l
to restore windows.)
x j Join this difference with the following
one. (C-u x j joins this difference with the
previous one.)
x s Split this difference into two differences.
Before you use this command,
position point in
each of the three buffers at the place where you want to
split the difference.
x t Trim identical lines off top and bottom of
the difference. Such lines occur when the A and B
versions are identical but differ from the ancestor
version.
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.
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 /* NEW */
version from B buffer
#endif /* 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 /* NEW */\n%b#endif /* NEW */\n"
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 gets ready to accept commands.
After setting up the merge, Emerge runs the hook emerge-startup-hook
(see section Hooks).
In addition to the facilities of typical programming language
major modes (see section Major
Modes for Programming Languages), C mode has various special
facilities.
- M-a M-e In C mode, M-a and M-e
move by complete C statements (
c-beginning-of-statement
and c-end-of-statement). These commands do
ordinary, textual sentence motion when in or next to a comment.
-
M-q M-q in C mode runs c-fill-paragraph,
which is designed for filling
C comments. (We assume you don't want to fill the actual
C code in a C program.)
C-c C-u Move back to the containing
preprocessor conditional, setting the mark at the starting point (c-up-conditional).
A numeric argument acts as a repeat count. With a
negative argument, this command
moves forward to the end of the containing preprocessor
conditional. When going backwards, #elif
acts like #else followed by #if.
When going forwards, #elif is ignored.
C-c C-n Move forward across the next
preprocessor conditional, setting the mark at the starting point (c-forward-conditional).
C-c C-p Move backward across the previous
preprocessor conditional, setting the at the starting point (c-backward-conditional).
M-x c-macro-expand When you are debugging C
code that uses macros, sometimes it is hard to figure out
precisely how the macros expand. The command M-x
c-macro-expand runs the C preprocessor and shows
you what expansion results from the region. The portion of
the buffer before the region is also included
in preprocessing, for the sake of macros defined there,
but the output from this part isn't shown.
M-x c-backslash-region
Insert or align \ characters at the ends
of the lines of the region,
except for the last such line. This is useful after
writing or editing a C macro definition.
If a line already ends in \, this command adjusts the
amount of whitespace
before it. Otherwise, it inserts a new \.
M-x cpp-highlight-buffer Highlight
parts of the text
according to its preprocessor conditionals. This command displays another buffer named *CPP
Edit*, which serves as a graphic menu for selecting how to display
particular kinds of conditionals and their contents.
After changing various settings, click on [A]pply
these settings (or go to that buffer and type a)
to rehighlight the C mode buffer
accordingly.
C++ mode is like C mode, except that it understands C++ comment syntax and certain other
differences between C and C++. It also has a command M-x fill-c++-comment, which fills a paragraph made of C++ comment lines.
The command comment-region is useful in
C++ mode for commenting out several consecutive lines, or
removing the commenting out of such lines. (You don't need this command with C comment syntax because you don't
need to put comment delimiters
on each line.) See section Manipulating
Comments.
Fortran mode provides special motion commands for Fortran
statements and subprograms, and indentation
commands that understand Fortran conventions of nesting, line
numbers and continuation statements. Fortran mode has its own
Auto Fill mode that breaks long lines into proper Fortran
continuation lines.
Special commands for comments are provided because Fortran
comments are unlike those of other languages. Built-in abbrevs
optionally save typing when you insert Fortran keywords.
Use M-x fortran-mode to switch to this major mode.
This command runs the hook fortran-mode-hook
(see section Hooks).
- Motion: Moving point by
statements or subprograms.
- Indent: Indentation
commands for Fortran.
- Comments: Inserting and
aligning comments.
- Autofill: Auto fill
minor mode for Fortran.
- Columns: Measuring
columns for valid Fortran.
- Abbrev: Built-in
abbrevs for Fortran keywords.
Fortran mode provides special commands to move by subprograms
(functions and subroutines) and by statements. There is also a command to put the region around one subprogram,
convenient for killing it or
moving it.
- C-M-a Move to beginning of subprogram (
beginning-of-fortran-subprogram). C-M-e
Move to end of subprogram (end-of-fortran-subprogram). C-M-h
Put point at
beginning of subprogram and mark at end (mark-fortran-subprogram). C-c
C-n Move to beginning of current or next statement (fortran-next-statement). C-c
C-p Move to beginning of current or previous
statement (fortran-previous-statement).
Special commands and features are needed for indenting Fortran
code in order to make sure various syntactic entities (line
numbers, comment line
indicators and continuation line flags) appear in the columns
that are required for standard Fortran.
- Commands: Commands for
indenting Fortran.
- Contline: How
continuation lines indent.
- Numbers: How line
numbers auto-indent.
- Conv: Conventions you
must obey to avoid trouble.
- Vars: Variables
controlling Fortran indent style.
- TAB Indent the current line (
fortran-indent-line). LFD
Indent the current and start a new indented line (fortran-indent-new-line). M-LFD
Break the current line and set up a continuation line. C-M-q
Indent all the lines of the subprogram point is in (fortran-indent-subprogram).
Fortran mode redefines TAB to reindent the current
line for Fortran (fortran-indent-line). This command indents Line numbers and
continuation markers to their required columns, and independently
indents the body of the statement based on its nesting in the
program.
The key LFD runs the command fortran-indent-new-line,
which reindents the current line then makes and indents a new
line. This command is useful
to reindent the closing statement of do loops and
other blocks before starting a new line.
The key C-M-q runs fortran-indent-subprogram,
a command to reindent all the
lines of the Fortran subprogram (function or subroutine)
containing point.
The key M-LFD runs fortran-split-line,
which splits a line in the appropriate fashion for Fortran. In a
non-comment line, the second
half becomes a continuation line and is indented accordingly. In
a comment line, both halves
become separate comment lines.
Most modern Fortran compilers allow two ways of writing
continuation lines. If the first non-space character on a line is in column
5, then that line is a continuation of the previous line. We call
this fixed format. (In GNU Emacs we always count
columns from 0.) The variable fortran-continuation-string specifies
what character to put on
column 5. A line that starts with a tab character followed by any digit
except 0 is also a continuation line. We call this
style of continuation tab format.
Fortran mode can make either style of continuation line, but
you must specify which one you prefer. The value of the variable indent-tabs-mode
controls the choice: nil for fixed format, and non-nil
for tab format. You can tell which style is presently in effect
by the presence or absence of the string Tab
in the mode line.
If the text on a line
starts with the conventional Fortran continuation marker $,
or if it begins with any non-whitespace character in column 5, Fortran
mode treats it as a continuation line. When you indent a
continuation line with TAB, it converts the line to
the current continuation style. When you split a Fortran
statement with M-LFD, the continuation marker on the newline is created according to
the continuation style.
The setting of continuation style affects several other
aspects of editing in Fortran mode. In fixed format mode, the
minimum column number for the body of a statement is 6. Lines
inside of Fortran blocks that are indented to larger column
numbers always use only the space character
for whitespace. In tab format
mode, the minimum column number for the statement body is 8, and
the whitespace before column
8 must always consist of one tab character.
When you enter Fortran mode for an existing file, it tries to
deduce the proper continuation style automatically from the file
contents. The first line that begins with either a tab character or six spaces
determines the choice. The variable fortran-analyze-depth
specifies how many lines to consider (at the beginning of the
file); if none of those lines indicates a style, then the variable fortran-tab-mode-default
specifies the style. If it is nil, that specifies
fixed format, and non-nil specifies tab format.
If a number is the first non-whitespace
in the line, Fortran indentation
assumes it is a line number and moves it to columns 0 through 4.
(Columns always count from 0 in GNU Emacs.)
Line numbers of four digits or less are normally indented one
space. The variable fortran-line-number-indent
controls this; it specifies the maximum indentation a line number can
have. Line numbers are indented to right-justify them to end in
column 4 unless that would require more than this maximum indentation. The default value of
the variable is 1.
Simply inserting a line number is enough to indent it
according to these rules. As each digit is inserted, the indentation is recomputed. To
turn off this feature, set the variable fortran-electric-line-number
to nil. Then inserting line numbers is like
inserting anything else.
Fortran mode assumes that you follow certain conventions that
simplify the task of understanding a Fortran program well enough
to indent it properly:
- Two nested do loops never share a continue
statement.
- Fortran keywords such as if, else, then, do
and others are written without embedded whitespace or line
breaks.
Fortran compilers generally ignore whitespace outside of string constants, but
Fortran mode does not recognize these keywords if they
are not contiguous. Constructs such as else if
or end do are acceptable, but the second
word should be on the same line as the first and not on a
continuation line.
If you fail to follow these conventions, the indentation commands may indent
some lines unaesthetically. However, a correct Fortran program
retains its meaning when reindented even if the conventions are
not followed.
Several additional variables control how Fortran indentation works:
- fortran-do-indent Extra indentation within each
level of do statement (default 3).
-
fortran-if-indent Extra indentation within each
level of if statement (default 3). This
value is also used for extra indentation within each
level of the Fortran 90 where statement.
fortran-structure-indent Extra indentation within each
level of structure, union, or map
statements (default 3).
fortran-continuation-indent Extra indentation for bodies of
continuation lines (default 5).
fortran-check-all-num-for-matching-do If this
is nil, indentation
assumes that each do statement ends on a continue
statement. Therefore, when computing indentation for a
statement other than continue, it can save
time by not checking for a do statement
ending there. If this is non-nil, indenting
any numbered statement must check for a do
that ends there. The default is nil.
fortran-blink-matching-if If this is t,
indenting an endif statement moves the cursor momentarily to the
matching if statement to show where it is.
The default is nil.
fortran-minimum-statement-indent-fixed Minimum indentation for fortran
statements when using fixed format continuation line
style. Statement bodies are never indented less than this
much. The default is 6.
fortran-minimum-statement-indent-tab Minimum indentation for fortran
statements for tab format continuation line style.
Statement bodies are never indented less than this much.
The default is 8.
The usual Emacs comment
commands assume that a comment
can follow a line of code. In Fortran, the standard comment syntax requires an entire
line to be just a comment.
Therefore, Fortran mode replaces the standard Emacs comment commands and defines some
new variables.
Fortran mode can also handle a nonstandard comment syntax where comments
start with ! and can follow other text. Because only some Fortran
compilers accept this syntax, Fortran mode will not insert such
comments unless you have said in advance to do so. To do this,
set the variable comment-start
to "!" (see section Variables).
- M-; Align comment
or insert new comment
(
fortran-comment-indent).
-
C-x ; Applies to nonstandard !
comments only.
C-c ; Turn all lines of the region into comments, or
(with argument) turn them back into real code (fortran-comment-region).
M-; in Fortran mode is redefined as the command fortran-comment-indent.
Like the usual M-; command,
this recognizes any kind of existing comment and aligns its text appropriately; if there is
no existing comment, a comment is inserted and aligned.
But inserting and aligning comments are not the same in Fortran
mode as in other modes.
When a new comment must be
inserted, if the current line is blank, a full-line comment is inserted. On a
non-blank line, a nonstandard ! comment is inserted if you have
said you want to use them. Otherwise a full-line comment is inserted on a new line
before the current line.
Nonstandard ! comments are aligned like comments
in other languages, but full-line comments are different. In a
standard full-line comment,
the comment delimiter itself
must always appear in column zero. What can be aligned is the text within the comment. You can choose from
three styles of alignment by setting the variable fortran-comment-indent-style
to one of these values:
- fixed Align the text
at a fixed column, which is the sum of
fortran-comment-line-extra-indent
and the minimum statement indentation.
This is the default.
-
The minimum statement indentation
is fortran-minimum-statement-indent-fixed
for fixed format continuation line style and fortran-minimum-statement-indent-tab
for tab format style.
relative Align the text as if it were a
line of code, but with an additional fortran-comment-line-extra-indent
columns of indentation.
nil Don't move text
in full-line columns automatically at all.
In addition, you can specify the character to be used to indent
within full-line comments by setting the variable fortran-comment-indent-char
to the single-character string you want to use.
Fortran mode introduces two variables comment-line-start
and comment-line-start-skip
which play for full-line comments the same roles played by comment-start
and comment-start-skip
for ordinary text-following
comments. Normally these are set properly by Fortran mode so you
do not need to change them.
The normal Emacs comment command C-x ; has not
been redefined. If you use ! comments, this command can be used with them.
Otherwise it is useless in Fortran mode.
The command C-c ;
(fortran-comment-region) turns all
the lines of the region into
comments by inserting the string C$$$
at the front of each one. With a numeric argument, it turns the region back into live code by
deleting C$$$ from the front of each line in it. The string used for these comments
can be controlled by setting the variable fortran-comment-region. Note that
here we have an example of a command
and a variable with the same
name; these two uses of the name never conflict because in Lisp
and in Emacs it is always clear from the context which one is
meant.
Fortran Auto Fill mode is a minor mode which automatically
splits Fortran statements as you insert them when they become too
wide. Splitting a statement involves making continuation lines
using fortran-continuation-string (See section Continuation Lines). This
splitting happens when you type SPC, RET,
or TAB, and also in the Fortran indentation commands.
M-x fortran-auto-fill-mode turns Fortran Auto Fill
mode on if it was off, or off if it was on. This command works the same as M-x
auto-fill-mode does for normal Auto Fill mode (see section Filling Text). A positive numeric
argument turns Fortran Auto Fill mode on, and a negative argument
turns it off. You can see when Fortran Auto Fill mode is in
effect by the presence of the word Fill in the mode
line, inside the parentheses. Fortran Auto Fill mode is a minor
mode, turned on or off for each buffer
individually. See section Minor
Modes.
Fortran Auto Fill mode breaks lines at spaces or delimiters
when the lines get longer than the desired width (the value of fill-column).
The delimiters that Fortran Auto Fill mode may break at are ,, ', +, -, /, *, =,
and ). The line break comes after the delimiter if
the variable fortran-break-before-delimiters
is nil. Otherwise (and by default), the break comes
before the delimiter.
By default, Fortran Auto Fill mode is not enabled. If you want
this feature turned on permanently, add a hook function to fortran-mode-hook
to execute (fortran-auto-fill-mode 1). See section Hooks.
- C-c C-r Display a ``column ruler'' momentarily
above the current line (
fortran-column-ruler). C-c
C-w Split the current window
horizontally temporarily so that it is 72 columns wide.
This may help you avoid making lines longer than the 72 character limit that some
fortran compilers impose (fortran-window-create-momentarily).
The command C-c C-r
(fortran-column-ruler) shows a column ruler
momentarily above the current line. The comment ruler is two lines of text that show you the locations
of columns with special significance in Fortran programs. Square
brackets show the limits of the columns for line numbers, and
curly brackets show the limits of the columns for the statement
body. Column numbers appear above them.
Note that the column numbers count from zero, as always in GNU
Emacs. As a result, the numbers may be one less than those you
are familiar with; but the positions they indicate in the line
are standard for Fortran.
The text used to display
the column ruler depends on the value of the variable indent-tabs-mode.
If indent-tabs-mode is nil, then the
value of the variable fortran-column-ruler-fixed
is used as the column ruler. Otherwise, the variable fortran-column-ruler-tab
is displayed. By changing these variables, you can change the
column ruler display.
For even more help, use C-c C-w (fortran-window-create),
a command which splits the
current window horizontally,
making a window 72 columns
wide. By editing in this window
you can immediately see when you make a line too wide to be
correct Fortran.
Fortran mode provides many built-in abbrevs for common
keywords and declarations. These are the same sort of abbrev that you can define
yourself. To use them, you must turn on Abbrev mode. See section Abbrevs.
The built-in abbrevs are unusual in one way: they all start
with a semicolon. You cannot normally use semicolon in an abbrev, but Fortran mode makes
this possible by changing the syntax of semicolon to ``word
constituent.''
For example, one built-in Fortran abbrev is ;c for continue.
If you insert ;c and then insert a punctuation character such as a space or a newline, the ;c
expands automatically to continue, provided Abbrev mode is enabled.
Type ;? or ;C-h to display a list of all the built-in Fortran
abbrevs and what they stand for.
Asm mode is a major mode for editing files of assembler code.
It defines these commands:
- TAB
tab-to-tab-stop. LFD
Insert a newline and
then indent using tab-to-tab-stop. :
Insert a colon and then remove the indentation from before
the label preceding colon. Then do tab-to-tab-stop. ;
Insert or align a comment.
The variable asm-comment-char
specifies which character
starts comments in assembler syntax.
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