man/indent.texi

   1 @c This is part of the Emacs manual.
   2 @c Copyright (C) 1985, 86, 87, 93, 94, 95, 1997, 2004 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 the effect of a preceding @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 lines in the region to the same column (@code{indent-region}).
  29 @item C-x @key{TAB}
  30 Shift lines in the region 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 Insert whitespace up to the next tab stop.  You can set tab stops at
  51 your choice of column positions, then type @kbd{M-i} to advance to the
  52 next tab stop.  The default tab stop settings have a tab stop every
  53 eight columns, which means by default @kbd{M-i} inserts a tab
  54 character.  To set the tab stops, use @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, most 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 when tabs are disabled for the indentation commands.
  79
  80 @menu
  81 * Indentation Commands::  Various commands and techniques for indentation.
  82 * Tab Stops::             You can set arbitrary "tab stops" and then
  83                             indent to the next tab stop when you want to.
  84 * Just Spaces::           You can request indentation using just spaces.
  85 @end menu
  86
  87 @node Indentation Commands, Tab Stops, Indentation, Indentation
  88 @section Indentation Commands and Techniques
  89
  90 @kindex M-m
  91 @findex back-to-indentation
  92   To move over the indentation on a line, do @kbd{M-m}
  93 (@code{back-to-indentation}).  This command, given anywhere on a line,
  94 positions point at the first nonblank character on the line, if any,
  95 or else at the end of the line.
  96
  97   To insert an indented line before the current line, do @kbd{C-a C-o
  98 @key{TAB}}.  To make an indented line after the current line, use
  99 @kbd{C-e C-j}.
 100
 101   If you just want to insert a tab character in the buffer, you can type
 102 @kbd{C-q @key{TAB}}.
 103
 104 @kindex C-M-o
 105 @findex split-line
 106   @kbd{C-M-o} (@code{split-line}) moves the text from point to the end of
 107 the line vertically down, so that the current line becomes two lines.
 108 @kbd{C-M-o} first moves point forward over any spaces and tabs.  Then it
 109 inserts after point a newline and enough indentation to reach the same
 110 column point is on.  Point remains before the inserted newline; in this
 111 regard, @kbd{C-M-o} resembles @kbd{C-o}.
 112
 113 @kindex M-^
 114 @findex delete-indentation
 115   To join two lines cleanly, use the @kbd{M-^}
 116 (@code{delete-indentation}) command.  It deletes the indentation at the
 117 front of the current line, and the line boundary as well, replacing them
 118 with a single space.  As a special case (useful for Lisp code) the
 119 single space is omitted if the characters to be joined are consecutive
 120 open parentheses or closing parentheses, or if the junction follows
 121 another newline.  To delete just the indentation of a line, go to the
 122 beginning of the line and use @kbd{M-\}
 123 (@code{delete-horizontal-space}), which deletes all spaces and tabs
 124 around the cursor.
 125
 126   If you have a fill prefix, @kbd{M-^} deletes the fill prefix if it
 127 appears after the newline that is deleted.  @xref{Fill Prefix}.
 128
 129 @kindex C-M-\
 130 @kindex C-x TAB
 131 @findex indent-region
 132 @findex indent-rigidly
 133   There are also commands for changing the indentation of several lines
 134 at once.  They apply to all the lines that begin in the region.
 135 @kbd{C-M-\} (@code{indent-region}) indents each line in the ``usual''
 136 way, as if you had typed @key{TAB} at the beginning of the line.  A
 137 numeric argument specifies the column to indent to, and each line is
 138 shifted left or right so that its first nonblank character appears in
 139 that column.  @kbd{C-x @key{TAB}} (@code{indent-rigidly}) moves all of
 140 the lines in the region right by its argument (left, for negative
 141 arguments).  The whole group of lines moves rigidly sideways, which is
 142 how the command gets its name.@refill
 143
 144 @cindex remove indentation
 145   If you want to remove all indentation from all of the line in the
 146 region, invoke @kbd{C-x @key{TAB}} with a large negative argument,
 147 such as -1000.
 148
 149 @findex indent-relative
 150   @kbd{M-x indent-relative} indents at point based on the previous line
 151 (actually, the last nonempty line).  It inserts whitespace at point, moving
 152 point, until it is underneath the next indentation point in the previous line.
 153 An indentation point is the end of a sequence of whitespace or the end of
 154 the line.  If point is farther right than any indentation point in the
 155 previous line, @code{indent-relative} runs @code{tab-to-tab-stop}
 156 @ifinfo
 157 (@pxref{Tab Stops}),
 158 @end ifinfo
 159 @iftex
 160 (see next section),
 161 @end iftex
 162 unless it is called with a numeric argument, in which case it does
 163 nothing.
 164
 165   @xref{Format Indentation}, for another way of specifying the
 166 indentation for part of your text.
 167
 168 @node Tab Stops, Just Spaces, Indentation Commands, Indentation
 169 @section Tab Stops
 170
 171 @cindex tab stops
 172 @cindex using tab stops in making tables
 173 @cindex tables, indentation for
 174 @kindex M-i
 175 @findex tab-to-tab-stop
 176   For typing in tables, you can use @kbd{M-i} (@code{tab-to-tab-stop}).
 177 This command inserts indentation before point, enough to reach the
 178 next tab stop column.
 179
 180 @findex edit-tab-stops
 181 @findex edit-tab-stops-note-changes
 182 @kindex C-c C-c @r{(Edit Tab Stops)}
 183 @vindex tab-stop-list
 184   You can specify the tab stops used by @kbd{M-i}.  They are stored in a
 185 variable called @code{tab-stop-list}, as a list of column-numbers in
 186 increasing order.
 187
 188   The convenient way to set the tab stops is with @kbd{M-x
 189 edit-tab-stops}, which creates and selects a buffer containing a
 190 description of the tab stop settings.  You can edit this buffer to
 191 specify different tab stops, and then type @kbd{C-c C-c} to make those
 192 new tab stops take effect.  The buffer uses Overwrite mode
 193 (@pxref{Minor Modes}).  @code{edit-tab-stops} records which buffer was
 194 current when you invoked it, and stores the tab stops back in that
 195 buffer; normally all buffers share the same tab stops and changing
 196 them in one buffer affects all, but if you happen to make
 197 @code{tab-stop-list} local in one buffer then @code{edit-tab-stops} in
 198 that buffer will edit the local settings.
 199
 200   Here is what the text representing the tab stops looks like for ordinary
 201 tab stops every eight columns.
 202
 203 @example
 204         :       :       :       :       :       :
 205 0         1         2         3         4
 206 0123456789012345678901234567890123456789012345678
 207 To install changes, type C-c C-c
 208 @end example
 209
 210   The first line contains a colon at each tab stop.  The remaining lines
 211 are present just to help you see where the colons are and know what to do.
 212
 213   Note that the tab stops that control @code{tab-to-tab-stop} have nothing
 214 to do with displaying tab characters in the buffer.  @xref{Display Custom},
 215 for more information on that.
 216
 217 @node Just Spaces,, Tab Stops, Indentation
 218 @section Tabs vs. Spaces
 219
 220 @vindex indent-tabs-mode
 221   Emacs normally uses both tabs and spaces to indent lines.  If you
 222 prefer, all indentation can be made from spaces only.  To request
 223 this, set @code{indent-tabs-mode} to @code{nil}.  This is a per-buffer
 224 variable, so altering the variable affects only the current buffer,
 225 but there is a default value which you can change as well.
 226 @xref{Locals}.
 227
 228   A tab is not always displayed in the same way.  By default, tabs are
 229 eight columns wide, but some people like to customize their tools to
 230 use a different tab width.  So by using spaces only, you can make sure
 231 that your file looks the same regardless of the tab width setting.
 232
 233 @findex tabify
 234 @findex untabify
 235   There are also commands to convert tabs to spaces or vice versa, always
 236 preserving the columns of all nonblank text.  @kbd{M-x tabify} scans the
 237 region for sequences of spaces, and converts sequences of at least two
 238 spaces to tabs if that can be done without changing indentation.  @kbd{M-x
 239 untabify} changes all tabs in the region to appropriate numbers of spaces.
 240
 241 @ignore
 242    arch-tag: acc07de7-ae11-4ee8-a159-cb59c473f0fb
 243 @end ignore