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206 lines
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206 lines
8.5 KiB
Plaintext
@c This is part of the Emacs manual.
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@c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc.
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@c See file emacs.texi for copying conditions.
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@node Indentation, Text, Major Modes, Top
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@chapter Indentation
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@cindex indentation
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@cindex columns (indentation)
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This chapter describes the Emacs commands that add, remove, or
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adjust indentation.
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@c WideCommands
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@table @kbd
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@item @key{TAB}
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Indent current line ``appropriately'' in a mode-dependent fashion.
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@item @kbd{C-j}
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Perform @key{RET} followed by @key{TAB} (@code{newline-and-indent}).
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@item M-^
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Merge two lines (@code{delete-indentation}). This would cancel out
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the effect of @kbd{C-j}.
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@item C-M-o
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Split line at point; text on the line after point becomes a new line
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indented to the same column that it now starts in (@code{split-line}).
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@item M-m
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Move (forward or back) to the first nonblank character on the current
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line (@code{back-to-indentation}).
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@item C-M-\
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Indent several lines to same column (@code{indent-region}).
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@item C-x @key{TAB}
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Shift block of lines rigidly right or left (@code{indent-rigidly}).
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@item M-i
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Indent from point to the next prespecified tab stop column
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(@code{tab-to-tab-stop}).
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@item M-x indent-relative
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Indent from point to under an indentation point in the previous line.
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@end table
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Most programming languages have some indentation convention. For Lisp
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code, lines are indented according to their nesting in parentheses. The
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same general idea is used for C code, though many details are different.
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@kindex TAB
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Whatever the language, to indent a line, use the @key{TAB} command. Each
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major mode defines this command to perform the sort of indentation
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appropriate for the particular language. In Lisp mode, @key{TAB} aligns
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the line according to its depth in parentheses. No matter where in the
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line you are when you type @key{TAB}, it aligns the line as a whole. In C
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mode, @key{TAB} implements a subtle and sophisticated indentation style that
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knows about many aspects of C syntax.
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In Text mode, @key{TAB} runs the command @code{tab-to-tab-stop}, which
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indents to the next tab stop column. You can set the tab stops with
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@kbd{M-x edit-tab-stops}.
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@menu
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* Indentation Commands:: Various commands and techniques for indentation.
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* Tab Stops:: You can set arbitrary "tab stops" and then
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indent to the next tab stop when you want to.
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* Just Spaces:: You can request indentation using just spaces.
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@end menu
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@node Indentation Commands, Tab Stops, Indentation, Indentation
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@section Indentation Commands and Techniques
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@kindex M-m
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@findex back-to-indentation
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To move over the indentation on a line, do @kbd{M-m}
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(@code{back-to-indentation}). This command, given anywhere on a line,
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positions point at the first nonblank character on the line.
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To insert an indented line before the current line, do @kbd{C-a C-o
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@key{TAB}}. To make an indented line after the current line, use
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@kbd{C-e C-j}.
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If you just want to insert a tab character in the buffer, you can type
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@kbd{C-q @key{TAB}}.
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@kindex C-M-o
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@findex split-line
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@kbd{C-M-o} (@code{split-line}) moves the text from point to the end of
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the line vertically down, so that the current line becomes two lines.
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@kbd{C-M-o} first moves point forward over any spaces and tabs. Then it
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inserts after point a newline and enough indentation to reach the same
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column point is on. Point remains before the inserted newline; in this
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regard, @kbd{C-M-o} resembles @kbd{C-o}.
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@kindex M-^
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@findex delete-indentation
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To join two lines cleanly, use the @kbd{M-^}
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(@code{delete-indentation}) command. It deletes the indentation at the
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front of the current line, and the line boundary as well, replacing them
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with a single space. As a special case (useful for Lisp code) the
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single space is omitted if the characters to be joined are consecutive
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open parentheses or closing parentheses, or if the junction follows
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another newline. To delete just the indentation of a line, go to the
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beginning of the line and use @kbd{M-\}
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(@code{delete-horizontal-space}), which deletes all spaces and tabs
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around the cursor.
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If you have a fill prefix, @kbd{M-^} deletes the fill prefix if it
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appears after the newline that is deleted. @xref{Fill Prefix}.
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@kindex C-M-\
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@kindex C-x TAB
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@findex indent-region
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@findex indent-rigidly
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There are also commands for changing the indentation of several lines
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at once. @kbd{C-M-\} (@code{indent-region}) applies to all the lines
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that begin in the region; it indents each line in the ``usual'' way, as
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if you had typed @key{TAB} at the beginning of the line. A numeric
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argument specifies the column to indent to, and each line is shifted
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left or right so that its first nonblank character appears in that
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column. @kbd{C-x @key{TAB}} (@code{indent-rigidly}) moves all of the
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lines in the region right by its argument (left, for negative
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arguments). The whole group of lines moves rigidly sideways, which is
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how the command gets its name.@refill
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@findex indent-relative
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@kbd{M-x indent-relative} indents at point based on the previous line
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(actually, the last nonempty line). It inserts whitespace at point, moving
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point, until it is underneath an indentation point in the previous line.
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An indentation point is the end of a sequence of whitespace or the end of
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the line. If point is farther right than any indentation point in the
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previous line, the whitespace before point is deleted and the first
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indentation point then applicable is used. If no indentation point is
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applicable even then, @code{indent-relative} runs @code{tab-to-tab-stop}
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@ifinfo
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(@pxref{Tab Stops}).
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@end ifinfo
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@iftex
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(see next section).
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@end iftex
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@code{indent-relative} is the definition of @key{TAB} in Indented Text
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mode. @xref{Text}.
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@xref{Format Indentation}, for another way of specifying the
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indentation for part of your text.
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@node Tab Stops, Just Spaces, Indentation Commands, Indentation
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@section Tab Stops
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@cindex tab stops
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@cindex using tab stops in making tables
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@cindex tables, indentation for
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@kindex M-i
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@findex tab-to-tab-stop
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For typing in tables, you can use Text mode's definition of @key{TAB},
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@code{tab-to-tab-stop}. This command inserts indentation before point,
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enough to reach the next tab stop column. If you are not in Text mode,
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this command can be found on the key @kbd{M-i}.
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@findex edit-tab-stops
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@findex edit-tab-stops-note-changes
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@kindex C-c C-c @r{(Edit Tab Stops)}
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@vindex tab-stop-list
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You can specify the tab stops used by @kbd{M-i}. They are stored in a
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variable called @code{tab-stop-list}, as a list of column-numbers in
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increasing order.
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The convenient way to set the tab stops is with @kbd{M-x
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edit-tab-stops}, which creates and selects a buffer containing a
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description of the tab stop settings. You can edit this buffer to
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specify different tab stops, and then type @kbd{C-c C-c} to make those
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new tab stops take effect. @code{edit-tab-stops} records which buffer
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was current when you invoked it, and stores the tab stops back in that
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buffer; normally all buffers share the same tab stops and changing them
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in one buffer affects all, but if you happen to make
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@code{tab-stop-list} local in one buffer then @code{edit-tab-stops} in
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that buffer will edit the local settings.
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Here is what the text representing the tab stops looks like for ordinary
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tab stops every eight columns.
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@example
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: : : : : :
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0 1 2 3 4
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0123456789012345678901234567890123456789012345678
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To install changes, type C-c C-c
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@end example
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The first line contains a colon at each tab stop. The remaining lines
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are present just to help you see where the colons are and know what to do.
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Note that the tab stops that control @code{tab-to-tab-stop} have nothing
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to do with displaying tab characters in the buffer. @xref{Display Vars},
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for more information on that.
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@node Just Spaces,, Tab Stops, Indentation
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@section Tabs vs. Spaces
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@vindex indent-tabs-mode
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Emacs normally uses both tabs and spaces to indent lines. If you prefer,
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all indentation can be made from spaces only. To request this, set
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@code{indent-tabs-mode} to @code{nil}. This is a per-buffer variable;
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altering the variable affects only the current buffer, but there is a
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default value which you can change as well. @xref{Locals}.
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@findex tabify
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@findex untabify
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There are also commands to convert tabs to spaces or vice versa, always
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preserving the columns of all nonblank text. @kbd{M-x tabify} scans the
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region for sequences of spaces, and converts sequences of at least three
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spaces to tabs if that can be done without changing indentation. @kbd{M-x
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untabify} changes all tabs in the region to appropriate numbers of spaces.
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