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Commands for Human Languages

The term text has two widespread meanings in our area of the computer field. One is data that is a sequence of characters. Any file that you edit with Emacs is text, in this sense of the word. The other meaning is more restrictive: a sequence of characters in a human language for humans to read (possibly after processing by a text formatter), as opposed to a program or commands for a program.

Human languages have syntactic/stylistic conventions that can be supported or used to advantage by editor commands: conventions involving words, sentences, paragraphs, and capital letters. This chapter describes Emacs commands for all of these things. There are also commands for filling, or rearranging paragraphs into lines of approximately equal length. The commands for moving over and killing words, sentences and paragraphs, while intended primarily for editing text, are also often useful for editing programs.

Emacs has several major modes for editing human language text. If the file contains text pure and simple, use Text mode, which customizes Emacs in small ways for the syntactic conventions of text. For text which contains embedded commands for text formatters, Emacs has other major modes, each for a particular text formatter. Thus, for input to TeX, you would use TeX mode; for input to nroff, Nroff mode.

Text Mode

Editing files of text in a human language ought to be done using Text mode rather than Lisp or Fundamental mode. Invoke M-x text-mode to enter Text mode. In Text mode, TAB runs the function tab-to-tab-stop, which allows you to use arbitrary tab stops set with M-x edit-tab-stops (see section Tab Stops). Features concerned with comments in programs are turned off except when explicitly invoked. The syntax table is changed so that periods are not considered part of a word, while apostrophes, backspaces and underlines are.

A similar variant mode is Indented Text mode, intended for editing text in which most lines are indented. This mode defines TAB to run indent-relative (see section Indentation), and makes Auto Fill indent the lines it creates. The result is that normally a line made by Auto Filling, or by LFD, is indented just like the previous line. Use M-x indented-text-mode to select this mode.

Entering Text mode or Indented Text mode calls with no arguments the value of the variable text-mode-hook, if that value exists and is not nil. This value is also called when modes related to Text mode are entered; this includes Nroff mode, TeX mode, Outline mode and Mail mode. Your hook can look at the value of major-mode to see which of these modes is actually being entered.

Nroff Mode

Nroff mode is a mode like Text mode but modified to handle nroff commands present in the text. Invoke M-x nroff-mode to enter this mode. It differs from Text mode in only a few ways. All nroff command lines are considered paragraph separators, so that filling will never garble the nroff commands. Pages are separated by `.bp' commands. Comments start with backslash-doublequote. Also, three special commands are provided that are not in Text mode:

M-n
Move to the beginning of the next line that isn't an nroff command (forward-text-line). An argument is a repeat count.
M-p
Like M-n but move up (backward-text-line).
M-?
Prints in the echo area the number of text lines (lines that are not nroff commands) in the region (count-text-lines).

The other feature of Nroff mode is Electric Nroff newline mode. This is a minor mode that you can turn on or off with M-x electric-nroff-mode (see section Minor Modes). When the mode is on, each time you use RET to end a line that contains an nroff command that opens a kind of grouping, it also inserts the matching nroff command to close that grouping, on the following line. For example, if you are at the beginning of a line and type . ( b RET, this inserts the matching command `.)b' on a new line following point.

Entering Nroff mode calls with no arguments the value of the variable text-mode-hook, if that value exists and is not nil; then it does the same with the variable nroff-mode-hook.

TeX Mode

TeX is a powerful text formatter written by Donald Knuth; it is also free, like GNU Emacs. LaTeX is a simplified input format for TeX, implemented by TeX macros. It comes with TeX.

Emacs has a special TeX mode for editing TeX input files. It provides facilities for checking the balance of delimiters and for invoking TeX on all or part of the file.

TeX mode has two variants, Plain TeX mode and LaTeX mode (actually two distinct major modes which differ only slightly). They are designed for editing the two different input formats. The command M-x tex-mode looks at the contents of the buffer to determine whether the contents appear to be LaTeX input or not; it then selects the appropriate mode. If it can't tell which is right (e.g., the buffer is empty), the variable TeX-default-mode controls which mode is used.

The commands M-x plain-tex-mode and M-x latex-mode explicitly select the two variants of TeX mode. Use these commands when M-x tex-mode does not guess right.

TeX for Unix systems can be obtained from the University of Washington for a distribution fee.

To order a full distribution, send $200.00 for a 1/2-inch 9-track 1600 bpi (tar or cpio) tape reel, or $210.00 for a 1/4-inch 4-track QIC-24 (tar or cpio) cartridge, to:

Northwest Computing Support Center
DR-10, Thomson Hall 35
University of Washington
Seattle, Washington 98195

Please make checks payable to the University of Washington.

Prepaid orders are preferred but purchase orders are acceptable; however, purchase orders carry an extra charge of $10.00, to pay for processing.

Overseas sites: please add to the base cost $20.00 for shipment via air parcel post, or $30.00 for shipment via courier.

Please check with the Northwest Computing Support Center at the University of Washington for current prices and formats:

telephone:  (206) 543-6259
email:      elisabet@u.washington.edu

TeX Editing Commands

Here are the special commands provided in TeX mode for editing the text of the file.

"
Insert, according to context, either ```' or `"' or `''' (TeX-insert-quote).
LFD
Insert a paragraph break (two newlines) and check the previous paragraph for unbalanced braces or dollar signs (TeX-terminate-paragraph).
M-x validate-TeX-buffer
Check each paragraph in the buffer for unbalanced braces or dollar signs.
M-{
Insert `{}' and position point between them (TeX-insert-braces).
M-}
Move forward past the next unmatched close brace (up-list).
C-c C-f
Close a block for LaTeX (TeX-close-LaTeX-block).

In TeX, the character `"' is not normally used; use `"' to start a quotation and `"' to end one. TeX mode defines the key " to insert `"' after whitespace or an open brace, `"' after a backslash, or `"' otherwise. This is done by the command TeX-insert-quote. If you need the character `"' itself in unusual contexts, use C-q to insert it. Also, " with a numeric argument always inserts that number of `"' characters.

In TeX mode, `$' has a special syntax code which attempts to understand the way TeX math mode delimiters match. When you insert a `$' that is meant to exit math mode, the position of the matching `$' that entered math mode is displayed for a second. This is the same feature that displays the open brace that matches a close brace that is inserted. However, there is no way to tell whether a `$' enters math mode or leaves it; so when you insert a `$' that enters math mode, the previous `$' position is shown as if it were a match, even though they are actually unrelated.

If you prefer to keep braces balanced at all times, you can use M-{ (TeX-insert-braces) to insert a pair of braces. It leaves point between the two braces so you can insert the text that belongs inside. Afterward, use the command M-} (up-list) to move forward past the close brace.

There are two commands for checking the matching of braces. LFD (TeX-terminate-paragraph) checks the paragraph before point, and inserts two newlines to start a new paragraph. It prints a message in the echo area if any mismatch is found. M-x validate-TeX-buffer checks the entire buffer, paragraph by paragraph. When it finds a paragraph that contains a mismatch, it displays point at the beginning of the paragraph for a few seconds and pushes a mark at that spot. Scanning continues until the whole buffer has been checked or until you type another key. The positions of the last several paragraphs with mismatches can be found in the mark ring (see section The Mark Ring).

Note that square brackets and parentheses are matched in TeX mode, not just braces. This is wrong for the purpose of checking TeX syntax. However, parentheses and square brackets are likely to be used in text as matching delimiters and it is useful for the various motion commands and automatic match display to work with them.

In LaTeX input, `\begin' and `\end' commands must balance. After you insert a `\begin', use C-c C-f (TeX-close-LaTeX-block) to insert automatically a matching `\end' (on a new line following the `\begin'). A blank line is inserted between the two, and point is left there.

TeX Printing Commands

You can invoke TeX as an inferior of Emacs on either the entire contents of the buffer or just a region at a time. Running TeX in this way on just one chapter is a good way to see what your changes look like without taking the time to format the entire file.

C-c C-r
Invoke TeX on the current region, plus the buffer's header (TeX-region).
C-c C-b
Invoke TeX on the entire current buffer (TeX-buffer).
C-c C-l
Recenter the window showing output from the inferior TeX so that the last line can be seen (TeX-recenter-output-buffer).
C-c C-k
Kill the inferior TeX (TeX-kill-job).
C-c C-p
Print the output from the last C-c C-r or C-c C-b command (TeX-print).
C-c C-q
Show the printer queue (TeX-show-print-queue).

You can pass the current buffer through an inferior TeX by means of C-c C-b (TeX-buffer). The formatted output appears in a file in `/tmp'; to print it, type C-c C-p (TeX-print). Afterward use C-c C-q (TeX-show-print-queue) to view the progress of your output towards being printed.

The console output from TeX, including any error messages, appears in a buffer called `*TeX-shell*'. If TeX gets an error, you can switch to this buffer and feed it input (this works as in Shell mode; see section Interactive Inferior Shell). Without switching to this buffer you can scroll it so that its last line is visible by typing C-c C-l.

Type C-c C-k (TeX-kill-job) to kill the TeX process if you see that its output is no longer useful. Using C-c C-b or C-c C-r also kills any TeX process still running.

You can also pass an arbitrary region through an inferior TeX by typing C-c C-r (TeX-region). This is tricky, however, because most files of TeX input contain commands at the beginning to set parameters and define macros, without which no later part of the file will format correctly. To solve this problem, C-c C-r allows you to designate a part of the file as containing essential commands; it is included before the specified region as part of the input to TeX. The designated part of the file is called the header.

To indicate the bounds of the header in Plain TeX mode, you insert two special strings in the file. Insert `%**start of header' before the header, and `%**end of header' after it. Each string must appear entirely on one line, but there may be other text on the line before or after. The lines containing the two strings are included in the header. If `%**start of header' does not appear within the first 100 lines of the buffer, C-c C-r assumes that there is no header.

In LaTeX mode, the header begins with `\documentstyle' and ends with `\begin{document}'. These are commands that LaTeX requires you to use in any case, so nothing special needs to be done to identify the header.

Entering either kind of TeX mode calls with no arguments the value of the variable text-mode-hook, if that value exists and is not nil; then it does the same with the variable TeX-mode-hook. Finally it does the same with either plain-TeX-mode-hook or LaTeX-mode-hook.

Texinfo Mode

Texinfo is a documentation system that uses a single source file to produce both on-line information and printed output. This means that instead of writing two different documents, one for the on-line help or other on-line information and the other for a typeset manual or other printed work, you need write only one document. When the work is revised, you need revise only one document. (You can read the on-line information, known as an Info file, with an Info documentation-reading program. @inforef{Top, info, info}, for more information about Info.) Texinfo is the format in which documentation for GNU utilities and libraries is written.

Texinfo mode provides special features for working with Texinfo files including utilities to construct Info menus and pointers automatically, keybindings to insert frequently used formatting commands, and keybindings for commands to format both for Info and for printing.

Texinfo mode is described in section 'Using Texinfo Mode' in Texinfo; The GNU Documentation Format.

Outline Mode

Outline mode is a major mode much like Text mode but intended for editing outlines. It allows you to make parts of the text temporarily invisible so that you can see just the overall structure of the outline. Type M-x outline-mode to turn on Outline mode in the current buffer.

Entering Outline mode calls with no arguments the value of the variable text-mode-hook, if that value exists and is not nil; then it does the same with the variable outline-mode-hook.

When a line is invisible in outline mode, it does not appear on the screen. The screen appears exactly as if the invisible line were deleted, except that an ellipsis (three periods in a row) appears at the end of the previous visible line (only one ellipsis no matter how many invisible lines follow).

All editing commands treat the text of the invisible line as part of the previous visible line. For example, C-n moves onto the next visible line. Killing an entire visible line, including its terminating newline, really kills all the following invisible lines along with it; yanking it all back yanks the invisible lines and they remain invisible.

Format of Outlines

Outline mode assumes that the lines in the buffer are of two types: heading lines and body lines. A heading line represents a topic in the outline. Heading lines start with one or more stars; the number of stars determines the depth of the heading in the outline structure. Thus, a heading line with one star is a major topic; all the heading lines with two stars between it and the next one-star heading are its subtopics; and so on. Any line that is not a heading line is a body line. Body lines belong to the preceding heading line. Here is an example:

* Food

This is the body,
which says something about the topic of food.

** Delicious Food

This is the body of the second-level header.

** Distasteful Food

This could have
a body too, with
several lines.

*** Dormitory Food

* Shelter

A second first-level topic with its header line.

A heading line together with all following body lines is called collectively an entry. A heading line together with all following deeper heading lines and their body lines is called a subtree.

You can customize the criterion for distinguishing heading lines by setting the variable outline-regexp. Any line whose beginning has a match for this regexp is considered a heading line. Matches that start within a line (not at the beginning) do not count. The length of the matching text determines the level of the heading; longer matches make a more deeply nested level. Thus, for example, if a text formatter has commands `@chapter', `@section' and `@subsection' to divide the document into chapters and sections, you could make those lines count as heading lines by setting outline-regexp to `"@chap\\|@\\(sub\\)*section"'. Note the trick: the two words `chapter' and `section' are equally long, but by defining the regexp to match only `chap' we ensure that the length of the text matched on a chapter heading is shorter, so that Outline mode will know that sections are contained in chapters. This works as long as no other command starts with `@chap'.

Outline mode makes a line invisible by changing the newline before it into an ASCII Control-M (code 015). Most editing commands that work on lines treat an invisible line as part of the previous line because, strictly speaking, it is part of that line, since there is no longer a newline in between. When you save the file in Outline mode, Control-M characters are saved as newlines, so the invisible lines become ordinary lines in the file. But saving does not change the visibility status of a line inside Emacs.

Outline Motion Commands

There are some special motion commands in Outline mode that move backward and forward to heading lines.

C-c C-n
Move point to the next visible heading line (outline-next-visible-heading).
C-c C-p
Move point to the previous visible heading line (outline-previous-visible-heading).
C-c C-f
Move point to the next visible heading line at the same level as the one point is on (outline-forward-same-level).
C-c C-b
Move point to the previous visible heading line at the same level (outline-backward-same-level).
C-c C-u
Move point up to a lower-level (more inclusive) visible heading line (outline-up-heading).

C-c C-n (next-visible-heading) moves down to the next heading line. C-c C-p (previous-visible-heading) moves similarly backward. Both accept numeric arguments as repeat counts. The names emphasize that invisible headings are skipped, but this is not really a special feature. All editing commands that look for lines ignore the invisible lines automatically.

More advanced motion commands understand the levels of headings. The two commands, C-c C-f (outline-forward-same-level) and C-c C-b (outline-backward-same-level), move from one heading line to another visible heading at the same depth in the outline. C-c C-u (outline-up-heading) moves backward to another heading that is less deeply nested.

Outline Visibility Commands

The other special commands of outline mode are used to make lines visible or invisible. Their names all start with hide or show. Most of them fall into pairs of opposites. They are not undoable; instead, you can undo right past them. Making lines visible or invisible is simply not recorded by the undo mechanism.

M-x hide-body
Make all body lines in the buffer invisible.
M-x show-all
Make all lines in the buffer visible.
C-c C-h
Make everything under this heading invisible, not including this heading itself (hide-subtree).
C-c C-s
Make everything under this heading visible, including body, subheadings, and their bodies (show-subtree).
M-x hide-leaves
Make the body of this heading line, and of all its subheadings, invisible.
M-x show-branches
Make all subheadings of this heading line, at all levels, visible.
C-c C-i
Make immediate subheadings (one level down) of this heading line visible (show-children).
M-x hide-entry
Make this heading line's body invisible.
M-x show-entry
Make this heading line's body visible.

Two commands that are exact opposites are M-x hide-entry and M-x show-entry. They are used with point on a heading line, and apply only to the body lines of that heading. The subtopics and their bodies are not affected.

Two more powerful opposites are C-c C-h (hide-subtree) and C-c C-s (show-subtree). Both expect to be used when point is on a heading line, and both apply to all the lines of that heading's subtree: its body, all its subheadings, both direct and indirect, and all of their bodies. In other words, the subtree contains everything following this heading line, up to and not including the next heading of the same or higher rank.

Intermediate between a visible subtree and an invisible one is having all the subheadings visible but none of the body. There are two commands for doing this, depending on whether you want to hide the bodies or make the subheadings visible. They are M-x hide-leaves and M-x show-branches.

A little weaker than show-branches is C-c C-i (show-children). It makes just the direct subheadings visible--those one level down. Deeper subheadings remain invisible, if they were invisible.

Two commands have a blanket effect on the whole file. M-x hide-body makes all body lines invisible, so that you see just the outline structure. M-x show-all makes all lines visible. These commands can be thought of as a pair of opposites even though M-x show-all applies to more than just body lines.

The use of ellipses at the ends of visible lines can be turned off by setting selective-display-ellipses to nil. Then there is no visible indication of the presence of invisible lines.

Words

Emacs has commands for moving over or operating on words. By convention, the keys for them are all Meta- characters.

M-f
Move forward over a word (forward-word).
M-b
Move backward over a word (backward-word).
M-d
Kill up to the end of a word (kill-word).
M-DEL
Kill back to the beginning of a word (backward-kill-word).
M-@
Mark the end of the next word (mark-word).
M-t
Transpose two words; drag a word forward or backward across other words (transpose-words).

Notice how these keys form a series that parallels the character-based C-f, C-b, C-d, C-t and DEL. M-@ is related to C-@, which is an alias for C-SPC.

The commands Meta-f (forward-word) and Meta-b (backward-word) move forward and backward over words. They are thus analogous to Control-f and Control-b, which move over single characters. Like their Control- analogues, Meta-f and Meta-b move several words if given an argument. Meta-f with a negative argument moves backward, and Meta-b with a negative argument moves forward. Forward motion stops right after the last letter of the word, while backward motion stops right before the first letter.

Meta-d (kill-word) kills the word after point. To be precise, it kills everything from point to the place Meta-f would move to. Thus, if point is in the middle of a word, Meta-d kills just the part after point. If some punctuation comes between point and the next word, it is killed along with the word. (If you wish to kill only the next word but not the punctuation before it, simply do Meta-f to get the end, and kill the word backwards with Meta-DEL.) Meta-d takes arguments just like Meta-f.

Meta-DEL (backward-kill-word) kills the word before point. It kills everything from point back to where Meta-b would move to. If point is after the space in `FOO, BAR', then `FOO, ' is killed. (If you wish to kill just `FOO', do Meta-b Meta-d instead of Meta-DEL.)

Meta-t (transpose-words) exchanges the word before or containing point with the following word. The delimiter characters between the words do not move. For example, `FOO, BAR' transposes into `BAR, FOO' rather than `BAR FOO,'. See section Transposing Text, for more on transposition and on arguments to transposition commands.

To operate on the next n words with an operation which applies between point and mark, you can either set the mark at point and then move over the words, or you can use the command Meta-@ (mark-word) which does not move point, but sets the mark where Meta-f would move to. It can be given arguments just like Meta-f.

The word commands' understanding of syntax is completely controlled by the syntax table. Any character can, for example, be declared to be a word delimiter. See section The Syntax Table.

Sentences

The Emacs commands for manipulating sentences and paragraphs are mostly on Meta- keys, so as to be like the word-handling commands.

M-a
Move back to the beginning of the sentence
(backward-sentence).
M-e
Move forward to the end of the sentence (forward-sentence).
M-k
Kill forward to the end of the sentence (kill-sentence).
C-x DEL
Kill back to the beginning of the sentence (backward-kill-sentence).

The commands Meta-a and Meta-e (backward-sentence and forward-sentence) move to the beginning and end of the current sentence, respectively. They were chosen to resemble Control-a and Control-e, which move to the beginning and end of a line. Unlike them, Meta-a and Meta-e if repeated or given numeric arguments move over successive sentences. Emacs assumes that the typist's convention is followed, and thus considers a sentence to end wherever there is a `.', `?' or `!' followed by the end of a line or two spaces, with any number of `)', `]', `'', or `"' characters allowed in between. A sentence also begins or ends wherever a paragraph begins or ends.

Neither M-a nor M-e moves past the newline or spaces beyond the sentence edge at which it is stopping.

Just as C-a and C-e have a kill command, C-k, to go with them, so M-a and M-e have a corresponding kill command M-k (kill-sentence) which kills from point to the end of the sentence. With minus one as an argument it kills back to the beginning of the sentence. Larger arguments serve as a repeat count.

There is a special command, C-x DEL (backward-kill-sentence) for killing back to the beginning of a sentence, because this is useful when you change your mind in the middle of composing text.

The variable sentence-end controls recognition of the end of a sentence. It is a regexp that matches the last few characters of a sentence, together with the whitespace following the sentence. Its normal value is

"[.?!][]\"')]*\\($\\|\t\\|  \\)[ \t\n]*"

This example is explained in the section on regexps. See section Syntax of Regular Expressions.

Paragraphs

The Emacs commands for manipulating paragraphs are also Meta- keys.

M-[
Move back to previous paragraph beginning
(backward-paragraph).
M-]
Move forward to next paragraph end (forward-paragraph).
M-h
Put point and mark around this or next paragraph (mark-paragraph).

Meta-[ moves to the beginning of the current or previous paragraph, while Meta-] moves to the end of the current or next paragraph. Blank lines and text formatter command lines separate paragraphs and are not part of any paragraph. Also, an indented line starts a new paragraph.

In major modes for programs (as opposed to Text mode), paragraphs begin and end only at blank lines. This makes the paragraph commands continue to be useful even though there are no paragraphs per se.

When there is a fill prefix, then paragraphs are delimited by all lines which don't start with the fill prefix. See section Filling Text.

When you wish to operate on a paragraph, you can use the command Meta-h (mark-paragraph) to set the region around it. This command puts point at the beginning and mark at the end of the paragraph point was in. If point is between paragraphs (in a run of blank lines, or at a boundary), the paragraph following point is surrounded by point and mark. If there are blank lines preceding the first line of the paragraph, one of these blank lines is included in the region. Thus, for example, M-h C-w kills the paragraph around or after point.

The precise definition of a paragraph boundary is controlled by the two variables paragraph-separate and paragraph-start. The value of paragraph-start is a regexp that should match any line that either starts or separates paragraphs. The value of paragraph-separate is another regexp that should match only lines that separate paragraphs without being part of any paragraph. Lines that start a new paragraph and are contained in it must match both regexps. For example, normally paragraph-start is "^[ \t\n\f]" and paragraph-separate is "^[ \t\f]*$".

Normally it is desirable for page boundaries to separate paragraphs. The default values of these variables recognize the usual separator for pages.

Pages

Files are often thought of as divided into pages by the formfeed character (ASCII Control-L, octal code 014). For example, if a file is printed on a line printer, each page of the file, in this sense, will start on a new page of paper. Emacs treats a page-separator character just like any other character. It can be inserted with C-q C-l, or deleted with DEL. Thus, you are free to paginate your file or not. However, since pages are often meaningful divisions of the file, commands are provided to move over them and operate on them.

C-x [
Move point to previous page boundary (backward-page).
C-x ]
Move point to next page boundary (forward-page).
C-x C-p
Put point and mark around this page (or another page) (mark-page).
C-x l
Count the lines in this page (count-lines-page).

The C-x [ (backward-page) command moves point to immediately after the previous page delimiter. If point is already right after a page delimiter, it skips that one and stops at the previous one. A numeric argument serves as a repeat count. The C-x ] (forward-page) command moves forward past the next page delimiter.

The C-x C-p command (mark-page) puts point at the beginning of the current page and the mark at the end. The page delimiter at the end is included (the mark follows it). The page delimiter at the front is excluded (point follows it). This command can be followed by C-w to kill a page which is to be moved elsewhere. If it is inserted after a page delimiter, at a place where C-x ] or C-x [ would take you, then the page will be properly delimited before and after once again.

A numeric argument to C-x C-p is used to specify which page to go to, relative to the current one. Zero means the current page. One means the next page, and -1 means the previous one.

The C-x l command (count-lines-page) is good for deciding where to break a page in two. It prints in the echo area the total number of lines in the current page, and then divides it up into those preceding the current line and those following, as in

Page has 96 (72+25) lines

Notice that the sum is off by one; this is correct if point is not at the beginning of a line.

The variable page-delimiter should have as its value a regexp that matches the beginning of a line that separates pages. This is what defines where pages begin. The normal value of this variable is "^\f", which matches a formfeed character at the beginning of a line.

Filling Text

With Auto Fill mode, text can be filled (broken up into lines that fit in a specified width) as you insert it. If you alter existing text it may no longer be properly filled; then explicit commands for filling can be used. (Filling is sometimes called "wrapping" in the terminology used for other text editors, but we don't use that term, because it could just as well refer to the continuation of long lines which happens in Emacs if you don't fill them.)

Auto Fill Mode

Auto Fill mode is a minor mode in which lines are broken automatically when they become too wide. Breaking happens only when you type a SPC or RET.

M-x auto-fill-mode
Enable or disable Auto Fill mode.
SPC
RET
In Auto Fill mode, break lines when appropriate.

M-x auto-fill-mode turns Auto Fill mode on if it was off, or off if it was on. With a positive numeric argument it always turns Auto Fill mode on, and with a negative argument always turns it off. You can see when Auto Fill mode is in effect by the presence of the word `Fill' in the mode line, inside the parentheses. Auto Fill mode is a minor mode, turned on or off for each buffer individually. See section Minor Modes.

In Auto Fill mode, lines are broken automatically at spaces when they get longer than the desired width. Line breaking and rearrangement takes place only when you type SPC or RET. If you wish to insert a space or newline without permitting line-breaking, type C-q SPC or C-q LFD (recall that a newline is really a linefeed). Also, C-o inserts a newline without line breaking.

Auto Fill mode works well with Lisp mode, because when it makes a new line in Lisp mode it indents that line with TAB. If a line ending in a comment gets too long, the text of the comment is split into two comment lines. Optionally new comment delimiters are inserted at the end of the first line and the beginning of the second so that each line is a separate comment; the variable comment-multi-line controls the choice (see section Manipulating Comments).

Auto Fill mode does not refill entire paragraphs. It can break lines but cannot merge lines. So editing in the middle of a paragraph can result in a paragraph that is not correctly filled. The easiest way to make the paragraph properly filled again is usually with the explicit fill commands.

Many users like Auto Fill mode and want to use it in all text files. The section on init files says how to arrange this permanently for yourself. See section The Init File, .emacs.

Explicit Fill Commands

M-q
Fill current paragraph (fill-paragraph).
M-g
Fill each paragraph in the region (fill-region).
C-x f
Set the fill column (set-fill-column).
M-x fill-region-as-paragraph.
Fill the region, considering it as one paragraph.
M-s
Center a line.

To refill a paragraph, use the command Meta-q (fill-paragraph). It causes the paragraph that point is inside, or the one after point if point is between paragraphs, to be refilled. All the line-breaks are removed, and then new ones are inserted where necessary. M-q can be undone with C-_. See section Undoing Changes.

To refill many paragraphs, use M-g (fill-region), which divides the region into paragraphs and fills each of them.

Meta-q and Meta-g use the same criteria as Meta-h for finding paragraph boundaries (see section Paragraphs). For more control, you can use M-x fill-region-as-paragraph, which refills everything between point and mark. This command recognizes no paragraph separators; it deletes any blank lines found within the region to be filled.

A numeric argument to M-g or M-q causes it to justify the text as well as filling it. This means that extra spaces are inserted to make the right margin line up exactly at the fill column. To remove the extra spaces, use M-q or M-g with no argument.

The command Meta-s (center-line) centers the current line within the current fill column. With an argument, it centers several lines individually and moves past them.

The maximum line width for filling is in the variable fill-column. Altering the value of fill-column makes it local to the current buffer; until that time, the default value is in effect. The default is initially 70. See section Local Variables.

The easiest way to set fill-column is to use the command C-x f (set-fill-column). With no argument, it sets fill-column to the current horizontal position of point. With a numeric argument, it uses that as the new fill column.

The Fill Prefix

To fill a paragraph in which each line starts with a special marker (which might be a few spaces, giving an indented paragraph), use the fill prefix feature. The fill prefix is a string which Emacs expects every line to start with, and which is not included in filling.

C-x .
Set the fill prefix (set-fill-prefix).
M-q
Fill a paragraph using current fill prefix (fill-paragraph).
M-x fill-individual-paragraphs
Fill the region, considering each change of indentation as starting a new paragraph.

To specify a fill prefix, move to a line that starts with the desired prefix, put point at the end of the prefix, and give the command C-x . (set-fill-prefix). That's a period after the C-x. To turn off the fill prefix, specify an empty prefix: type C-x . with point at the beginning of a line.

When a fill prefix is in effect, the fill commands remove the fill prefix from each line before filling and insert it on each line after filling. The fill prefix is also inserted on new lines made automatically by Auto Fill mode. Lines that do not start with the fill prefix are considered to start paragraphs, both in M-q and the paragraph commands; this is just right if you are using paragraphs with hanging indentation (every line indented except the first one). Lines which are blank or indented once the prefix is removed also separate or start paragraphs; this is what you want if you are writing multi-paragraph comments with a comment delimiter on each line.

The fill prefix is stored in the variable fill-prefix. Its value is a string, or nil when there is no fill prefix. This is a per-buffer variable; altering the variable affects only the current buffer, but there is a default value which you can change as well. See section Local Variables.

Another way to use fill prefixes is through M-x fill-individual-paragraphs. This function divides the region into groups of consecutive lines with the same amount and kind of indentation and fills each group as a paragraph using its indentation as a fill prefix.

Case Conversion Commands

Emacs has commands for converting either a single word or any arbitrary range of text to upper case or to lower case.

M-l
Convert following word to lower case (downcase-word).
M-u
Convert following word to upper case (upcase-word).
M-c
Capitalize the following word (capitalize-word).
C-x C-l
Convert region to lower case (downcase-region).
C-x C-u
Convert region to upper case (upcase-region).

The word conversion commands are the most useful. Meta-l (downcase-word) converts the word after point to lower case, moving past it. Thus, repeating Meta-l converts successive words. Meta-u (upcase-word) converts to all capitals instead, while Meta-c (capitalize-word) puts the letter following point into upper case and the rest of the letters in the word into lower case. All these commands convert several words at once if given an argument. They are especially convenient for converting a large amount of text from all upper case to mixed case, because you can move through the text using M-l, M-u or M-c on each word as appropriate, occasionally using M-f instead to skip a word.

When given a negative argument, the word case conversion commands apply to the appropriate number of words before point, but do not move point. This is convenient when you have just typed a word in the wrong case: you can give the case conversion command and continue typing.

If a word case conversion command is given in the middle of a word, it applies only to the part of the word which follows point. This is just like what Meta-d (kill-word) does. With a negative argument, case conversion applies only to the part of the word before point.

The other case conversion commands are C-x C-u (upcase-region) and C-x C-l (downcase-region), which convert everything between point and mark to the specified case. Point and mark do not move.

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