man/indent.texi

   1 @c This is part of the Emacs manual.
   2 @c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997 Free Software Foundation, Inc.
   3 @c See file emacs.texi for copying conditions.
   4 @node Indentation, Text, Major Modes, Top
   5 @chapter Indentation
   6 @cindex indentation
   7 @cindex columns (indentation)
   8
   9   This chapter describes the Emacs commands that add, remove, or
  10 adjust indentation.
  11
  12 @table @kbd
  13 @item @key{TAB}
  14 Indent the current line ``appropriately'' in a mode-dependent fashion.
  15 @item @kbd{C-j}
  16 Perform @key{RET} followed by @key{TAB} (@code{newline-and-indent}).
  17 @item M-^
  18 Merge the previous and the current line (@code{delete-indentation}).
  19 This would cancel out the effect of @kbd{C-j}.
  20 @item C-M-o
  21 Split the current line at point; text on the line after point becomes a
  22 new line indented to the same column where point is located
  23 (@code{split-line}).
  24 @item M-m
  25 Move (forward or back) to the first nonblank character on the current
  26 line (@code{back-to-indentation}).
  27 @item C-M-\
  28 Indent several lines to the same column (@code{indent-region}).
  29 @item C-x @key{TAB}
  30 Shift a block of lines rigidly right or left (@code{indent-rigidly}).
  31 @item M-i
  32 Indent from point to the next prespecified tab stop column
  33 (@code{tab-to-tab-stop}).
  34 @item M-x indent-relative
  35 Indent from point to under an indentation point in the previous line.
  36 @end table
  37
  38   Most programming languages have some indentation convention.  For Lisp
  39 code, lines are indented according to their nesting in parentheses.  The
  40 same general idea is used for C code, though many details are different.
  41
  42 @kindex TAB
  43   Whatever the language, to indent a line, use the @key{TAB} command.  Each
  44 major mode defines this command to perform the sort of indentation
  45 appropriate for the particular language.  In Lisp mode, @key{TAB} aligns
  46 the line according to its depth in parentheses.  No matter where in the
  47 line you are when you type @key{TAB}, it aligns the line as a whole.  In C
  48 mode, @key{TAB} implements a subtle and sophisticated indentation style that
  49 knows about many aspects of C syntax.
  50
  51   In Text mode, @key{TAB} runs the command @code{tab-to-tab-stop}, which
  52 indents to the next tab stop column.  You can set the tab stops with
  53 @kbd{M-x edit-tab-stops}.
  54
  55   Normally, @key{TAB} inserts an optimal mix of tabs and spaces for
  56 the intended indentation.  @xref{Just Spaces}, for how to prevent use
  57 of tabs.
  58
  59 @menu
  60 * Indentation Commands::  Various commands and techniques for indentation.
  61 * Tab Stops::             You can set arbitrary "tab stops" and then
  62                             indent to the next tab stop when you want to.
  63 * Just Spaces::           You can request indentation using just spaces.
  64 @end menu
  65
  66 @node Indentation Commands, Tab Stops, Indentation, Indentation
  67 @section Indentation Commands and Techniques
  68
  69 @kindex M-m
  70 @findex back-to-indentation
  71   To move over the indentation on a line, do @kbd{M-m}
  72 (@code{back-to-indentation}).  This command, given anywhere on a line,
  73 positions point at the first nonblank character on the line.
  74
  75   To insert an indented line before the current line, do @kbd{C-a C-o
  76 @key{TAB}}.  To make an indented line after the current line, use
  77 @kbd{C-e C-j}.
  78
  79   If you just want to insert a tab character in the buffer, you can type
  80 @kbd{C-q @key{TAB}}.
  81
  82 @kindex C-M-o
  83 @findex split-line
  84   @kbd{C-M-o} (@code{split-line}) moves the text from point to the end of
  85 the line vertically down, so that the current line becomes two lines.
  86 @kbd{C-M-o} first moves point forward over any spaces and tabs.  Then it
  87 inserts after point a newline and enough indentation to reach the same
  88 column point is on.  Point remains before the inserted newline; in this
  89 regard, @kbd{C-M-o} resembles @kbd{C-o}.
  90
  91 @kindex M-^
  92 @findex delete-indentation
  93   To join two lines cleanly, use the @kbd{M-^}
  94 (@code{delete-indentation}) command.  It deletes the indentation at the
  95 front of the current line, and the line boundary as well, replacing them
  96 with a single space.  As a special case (useful for Lisp code) the
  97 single space is omitted if the characters to be joined are consecutive
  98 open parentheses or closing parentheses, or if the junction follows
  99 another newline.  To delete just the indentation of a line, go to the
 100 beginning of the line and use @kbd{M-\}
 101 (@code{delete-horizontal-space}), which deletes all spaces and tabs
 102 around the cursor.
 103
 104   If you have a fill prefix, @kbd{M-^} deletes the fill prefix if it
 105 appears after the newline that is deleted.  @xref{Fill Prefix}.
 106
 107 @kindex C-M-\
 108 @kindex C-x TAB
 109 @findex indent-region
 110 @findex indent-rigidly
 111   There are also commands for changing the indentation of several lines
 112 at once.  @kbd{C-M-\} (@code{indent-region}) applies to all the lines
 113 that begin in the region; it indents each line in the ``usual'' way, as
 114 if you had typed @key{TAB} at the beginning of the line.  A numeric
 115 argument specifies the column to indent to, and each line is shifted
 116 left or right so that its first nonblank character appears in that
 117 column.  @kbd{C-x @key{TAB}} (@code{indent-rigidly}) moves all of the
 118 lines in the region right by its argument (left, for negative
 119 arguments).  The whole group of lines moves rigidly sideways, which is
 120 how the command gets its name.@refill
 121
 122 @cindex remove indentation
 123   If you want to remove all indentation from all of the line in the
 124 region, invoke @kbd{C-x @key{TAB}} with a large negative argument,
 125 such as -1000.
 126
 127 @findex indent-relative
 128   @kbd{M-x indent-relative} indents at point based on the previous line
 129 (actually, the last nonempty line).  It inserts whitespace at point, moving
 130 point, until it is underneath an indentation point in the previous line.
 131 An indentation point is the end of a sequence of whitespace or the end of
 132 the line.  If point is farther right than any indentation point in the
 133 previous line, the whitespace before point is deleted and the first
 134 indentation point then applicable is used.  If no indentation point is
 135 applicable even then, @code{indent-relative} runs @code{tab-to-tab-stop}
 136 @ifinfo
 137 (@pxref{Tab Stops}),
 138 @end ifinfo
 139 @iftex
 140 (see next section),
 141 @end iftex
 142 unless it is called with a numeric argument, in which case it does
 143 nothing.
 144
 145   @code{indent-relative} is the definition of @key{TAB} in Indented Text
 146 mode.  @xref{Text}.
 147
 148   @xref{Format Indentation}, for another way of specifying the
 149 indentation for part of your text.
 150
 151 @node Tab Stops, Just Spaces, Indentation Commands, Indentation
 152 @section Tab Stops
 153
 154 @cindex tab stops
 155 @cindex using tab stops in making tables
 156 @cindex tables, indentation for
 157 @kindex M-i
 158 @findex tab-to-tab-stop
 159   For typing in tables, you can use Text mode's definition of @key{TAB},
 160 @code{tab-to-tab-stop}.  This command inserts indentation before point,
 161 enough to reach the next tab stop column.  If you are not in Text mode,
 162 this command can be found on the key @kbd{M-i}.
 163
 164 @findex edit-tab-stops
 165 @findex edit-tab-stops-note-changes
 166 @kindex C-c C-c @r{(Edit Tab Stops)}
 167 @vindex tab-stop-list
 168   You can specify the tab stops used by @kbd{M-i}.  They are stored in a
 169 variable called @code{tab-stop-list}, as a list of column-numbers in
 170 increasing order.
 171
 172   The convenient way to set the tab stops is with @kbd{M-x
 173 edit-tab-stops}, which creates and selects a buffer containing a
 174 description of the tab stop settings.  You can edit this buffer to
 175 specify different tab stops, and then type @kbd{C-c C-c} to make those
 176 new tab stops take effect.  @code{edit-tab-stops} records which buffer
 177 was current when you invoked it, and stores the tab stops back in that
 178 buffer; normally all buffers share the same tab stops and changing them
 179 in one buffer affects all, but if you happen to make
 180 @code{tab-stop-list} local in one buffer then @code{edit-tab-stops} in
 181 that buffer will edit the local settings.
 182
 183   Here is what the text representing the tab stops looks like for ordinary
 184 tab stops every eight columns.
 185
 186 @example
 187         :       :       :       :       :       :
 188 0         1         2         3         4
 189 0123456789012345678901234567890123456789012345678
 190 To install changes, type C-c C-c
 191 @end example
 192
 193   The first line contains a colon at each tab stop.  The remaining lines
 194 are present just to help you see where the colons are and know what to do.
 195
 196   Note that the tab stops that control @code{tab-to-tab-stop} have nothing
 197 to do with displaying tab characters in the buffer.  @xref{Display Custom},
 198 for more information on that.
 199
 200 @node Just Spaces,, Tab Stops, Indentation
 201 @section Tabs vs. Spaces
 202
 203 @vindex indent-tabs-mode
 204   Emacs normally uses both tabs and spaces to indent lines.  If you
 205 prefer, all indentation can be made from spaces only.  To request
 206 this, set @code{indent-tabs-mode} to @code{nil}.  This is a per-buffer
 207 variable, so altering the variable affects only the current buffer,
 208 but there is a default value which you can change as well.
 209 @xref{Locals}.
 210
 211 @findex tabify
 212 @findex untabify
 213   There are also commands to convert tabs to spaces or vice versa, always
 214 preserving the columns of all nonblank text.  @kbd{M-x tabify} scans the
 215 region for sequences of spaces, and converts sequences of at least three
 216 spaces to tabs if that can be done without changing indentation.  @kbd{M-x
 217 untabify} changes all tabs in the region to appropriate numbers of spaces.