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   Emacs supports four general categories of operations that could all
  39 be called `indentation':
  40
  41 @enumerate
  42 @item
  43 Insert a tab character.  You can type @kbd{C-q @key{TAB}} to do this.
  44
  45 A tab character is displayed as a stretch of whitespace which extends
  46 to the next display tab stop position, and the default width of a tab
  47 stop is eight.  @xref{Display Custom}, for more details.
  48
  49 @item
  50 Advance to the next tab stop.  You can set tab stops at your choice of
  51 column positions, then type @kbd{M-i} to advance to the next tab stop.
  52 The default is to have tab stops every eight columns, which means by
  53 default @kbd{M-i} inserts a tab character.  To set the tab stops, use
  54 @kbd{M-x edit-tab-stops}.
  55
  56 @item
  57 Align a line with the previous line.  More precisely, the command
  58 @kbd{M-x indent-relative} indents the current line under the beginning
  59 of some word in the previous line.  In Fundamental mode and in Text
  60 mode, @key{TAB} runs the command @code{indent-relative}.
  61
  62 @item
  63 The most sophisticated method is @dfn{syntax-driven indentation}.
  64 Most programming languages have an indentation convention.  For Lisp
  65 code, lines are indented according to their nesting in parentheses.  C
  66 code uses the same general idea, but many details are different.
  67
  68 @kindex TAB
  69 Type @key{TAB} to do syntax-driven indentation, in a mode that
  70 supports it.  It realigns the current line according with the syntax
  71 of the preceding lines.  No matter where in the line you are when you
  72 type @key{TAB}, it aligns the line as a whole.
  73 @end enumerate
  74
  75   Normally, all of the above methods insert an optimal mix of tabs and
  76 spaces to align to the desired column.  @xref{Just Spaces}, for how to
  77 disable use of tabs.  However, @kbd{C-q @key{TAB}} always inserts a
  78 tab, even they are disabled for the indentation commands.
  79
  80 @c   In Text mode, @key{TAB} runs the command @code{tab-to-tab-stop}, which
  81 @c indents to the next tab stop column.  You can set the tab stops with
  82 @c @kbd{M-x edit-tab-stops}.
  83
  84 @menu
  85 * Indentation Commands::  Various commands and techniques for indentation.
  86 * Tab Stops::             You can set arbitrary "tab stops" and then
  87                             indent to the next tab stop when you want to.
  88 * Just Spaces::           You can request indentation using just spaces.
  89 @end menu
  90
  91 @node Indentation Commands, Tab Stops, Indentation, Indentation
  92 @section Indentation Commands and Techniques
  93
  94 @kindex M-m
  95 @findex back-to-indentation
  96   To move over the indentation on a line, do @kbd{M-m}
  97 (@code{back-to-indentation}).  This command, given anywhere on a line,
  98 positions point at the first nonblank character on the line.
  99
 100   To insert an indented line before the current line, do @kbd{C-a C-o
 101 @key{TAB}}.  To make an indented line after the current line, use
 102 @kbd{C-e C-j}.
 103
 104   If you just want to insert a tab character in the buffer, you can type
 105 @kbd{C-q @key{TAB}}.
 106
 107 @kindex C-M-o
 108 @findex split-line
 109   @kbd{C-M-o} (@code{split-line}) moves the text from point to the end of
 110 the line vertically down, so that the current line becomes two lines.
 111 @kbd{C-M-o} first moves point forward over any spaces and tabs.  Then it
 112 inserts after point a newline and enough indentation to reach the same
 113 column point is on.  Point remains before the inserted newline; in this
 114 regard, @kbd{C-M-o} resembles @kbd{C-o}.
 115
 116 @kindex M-^
 117 @findex delete-indentation
 118   To join two lines cleanly, use the @kbd{M-^}
 119 (@code{delete-indentation}) command.  It deletes the indentation at the
 120 front of the current line, and the line boundary as well, replacing them
 121 with a single space.  As a special case (useful for Lisp code) the
 122 single space is omitted if the characters to be joined are consecutive
 123 open parentheses or closing parentheses, or if the junction follows
 124 another newline.  To delete just the indentation of a line, go to the
 125 beginning of the line and use @kbd{M-\}
 126 (@code{delete-horizontal-space}), which deletes all spaces and tabs
 127 around the cursor.
 128
 129   If you have a fill prefix, @kbd{M-^} deletes the fill prefix if it
 130 appears after the newline that is deleted.  @xref{Fill Prefix}.
 131
 132 @kindex C-M-\
 133 @kindex C-x TAB
 134 @findex indent-region
 135 @findex indent-rigidly
 136   There are also commands for changing the indentation of several lines
 137 at once.  @kbd{C-M-\} (@code{indent-region}) applies to all the lines
 138 that begin in the region; it indents each line in the ``usual'' way, as
 139 if you had typed @key{TAB} at the beginning of the line.  A numeric
 140 argument specifies the column to indent to, and each line is shifted
 141 left or right so that its first nonblank character appears in that
 142 column.  @kbd{C-x @key{TAB}} (@code{indent-rigidly}) moves all of the
 143 lines in the region right by its argument (left, for negative
 144 arguments).  The whole group of lines moves rigidly sideways, which is
 145 how the command gets its name.@refill
 146
 147 @cindex remove indentation
 148   If you want to remove all indentation from all of the line in the
 149 region, invoke @kbd{C-x @key{TAB}} with a large negative argument,
 150 such as -1000.
 151
 152 @findex indent-relative
 153   @kbd{M-x indent-relative} indents at point based on the previous line
 154 (actually, the last nonempty line).  It inserts whitespace at point, moving
 155 point, until it is underneath an indentation point in the previous line.
 156 An indentation point is the end of a sequence of whitespace or the end of
 157 the line.  If point is farther right than any indentation point in the
 158 previous line, the whitespace before point is deleted and the first
 159 indentation point then applicable is used.  If no indentation point is
 160 applicable even then, @code{indent-relative} runs @code{tab-to-tab-stop}
 161 @ifinfo
 162 (@pxref{Tab Stops}),
 163 @end ifinfo
 164 @iftex
 165 (see next section),
 166 @end iftex
 167 unless it is called with a numeric argument, in which case it does
 168 nothing.
 169
 170   @code{indent-relative} is the definition of @key{TAB} in Indented Text
 171 mode.  @xref{Text}.
 172
 173   @xref{Format Indentation}, for another way of specifying the
 174 indentation for part of your text.
 175
 176 @node Tab Stops, Just Spaces, Indentation Commands, Indentation
 177 @section Tab Stops
 178
 179 @cindex tab stops
 180 @cindex using tab stops in making tables
 181 @cindex tables, indentation for
 182 @kindex M-i
 183 @findex tab-to-tab-stop
 184   For typing in tables, you can use Text mode's definition of @key{TAB},
 185 @code{tab-to-tab-stop}.  This command inserts indentation before point,
 186 enough to reach the next tab stop column.  If you are not in Text mode,
 187 this command can be found on the key @kbd{M-i}.
 188
 189 @findex edit-tab-stops
 190 @findex edit-tab-stops-note-changes
 191 @kindex C-c C-c @r{(Edit Tab Stops)}
 192 @vindex tab-stop-list
 193   You can specify the tab stops used by @kbd{M-i}.  They are stored in a
 194 variable called @code{tab-stop-list}, as a list of column-numbers in
 195 increasing order.
 196
 197   The convenient way to set the tab stops is with @kbd{M-x
 198 edit-tab-stops}, which creates and selects a buffer containing a
 199 description of the tab stop settings.  You can edit this buffer to
 200 specify different tab stops, and then type @kbd{C-c C-c} to make those
 201 new tab stops take effect.  @code{edit-tab-stops} records which buffer
 202 was current when you invoked it, and stores the tab stops back in that
 203 buffer; normally all buffers share the same tab stops and changing them
 204 in one buffer affects all, but if you happen to make
 205 @code{tab-stop-list} local in one buffer then @code{edit-tab-stops} in
 206 that buffer will edit the local settings.
 207
 208   Here is what the text representing the tab stops looks like for ordinary
 209 tab stops every eight columns.
 210
 211 @example
 212         :       :       :       :       :       :
 213 0         1         2         3         4
 214 0123456789012345678901234567890123456789012345678
 215 To install changes, type C-c C-c
 216 @end example
 217
 218   The first line contains a colon at each tab stop.  The remaining lines
 219 are present just to help you see where the colons are and know what to do.
 220
 221   Note that the tab stops that control @code{tab-to-tab-stop} have nothing
 222 to do with displaying tab characters in the buffer.  @xref{Display Custom},
 223 for more information on that.
 224
 225 @node Just Spaces,, Tab Stops, Indentation
 226 @section Tabs vs. Spaces
 227
 228 @vindex indent-tabs-mode
 229   Emacs normally uses both tabs and spaces to indent lines.  If you
 230 prefer, all indentation can be made from spaces only.  To request
 231 this, set @code{indent-tabs-mode} to @code{nil}.  This is a per-buffer
 232 variable, so altering the variable affects only the current buffer,
 233 but there is a default value which you can change as well.
 234 @xref{Locals}.
 235
 236   A tab is not always displayed in the same way.  By default, tabs are
 237 eight columns wide, but some people like to customize their tools to
 238 use a different tab width.  So by using spaces only, you can make sure
 239 that your file looks the same regardless of the tab width setting.
 240
 241 @findex tabify
 242 @findex untabify
 243   There are also commands to convert tabs to spaces or vice versa, always
 244 preserving the columns of all nonblank text.  @kbd{M-x tabify} scans the
 245 region for sequences of spaces, and converts sequences of at least three
 246 spaces to tabs if that can be done without changing indentation.  @kbd{M-x
 247 untabify} changes all tabs in the region to appropriate numbers of spaces.
 248
 249 @ignore
 250    arch-tag: acc07de7-ae11-4ee8-a159-cb59c473f0fb
 251 @end ignore