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1
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2 @node Buffers, Windows, Files, Top
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3 @chapter Using Multiple Buffers
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4
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5 @cindex buffers
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6 Text you are editing in Emacs resides in an object called a
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7 @dfn{buffer}. Each time you visit a file, Emacs creates a buffer to
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8 hold the file's text. Each time you invoke Dired, Emacs creates a buffer
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9 to hold the directory listing. If you send a message with @kbd{C-x m},
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10 a buffer named @samp{*mail*} is used to hold the text of the message.
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11 When you ask for a command's documentation, it appears in a buffer
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12 called @samp{*Help*}.
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13
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14 @cindex selected buffer
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15 @cindex current buffer
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16 At any time, one and only one buffer is @dfn{selected}. It is also
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17 called the @dfn{current buffer}. Saying a command operates on ``the
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18 buffer'' really means that the command operates on the selected
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19 buffer, as most commands do.
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20
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21 When Emacs creates multiple windows, each window has a chosen buffer which
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22 is displayed there, but at any time only one of the windows is selected and
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23 its chosen buffer is the selected buffer. Each window's mode line displays
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24 the name of the buffer the window is displaying (@pxref{Windows}).
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25
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26 Each buffer has a name which can be of any length but is
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27 case-sensitive. You can select a buffer using its name. Most
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28 buffers are created when you visit files; their names are derived from
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29 the files' names. You can also create an empty buffer with any name you
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30 want. A newly started Emacs has a buffer named @samp{*scratch*} which
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31 you can use for evaluating Lisp expressions in Emacs.
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32
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33 Each buffer records what file it is visiting, whether it is
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34 modified, and what major mode and minor modes are in effect in it
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35 (@pxref{Major Modes}). Any Emacs variable can be made @dfn{local to} a
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36 particular buffer, meaning its value in that buffer can be different from
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37 the value in other buffers. @xref{Locals}.
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38
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39 @menu
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40 * Select Buffer:: Creating a new buffer or reselecting an old one.
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41 * List Buffers:: Getting a list of buffers that exist.
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42 * Misc Buffer:: Renaming; changing read-onliness; copying text.
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43 * Kill Buffer:: Killing buffers you no longer need.
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44 * Several Buffers:: How to go through the list of all buffers
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45 and operate variously on several of them.
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46 @end menu
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47
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48 @node Select Buffer, List Buffers, Buffers, Buffers
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49 @section Creating and Selecting Buffers
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50 @cindex changing buffers
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51 @cindex switching buffers
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52
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53 @table @kbd
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54 @item C-x b @var{buffer} @key{RET}
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55 Select or create a buffer named @var{buffer} (@code{switch-to-buffer}).
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56 @item C-x 4 b @var{buffer} @key{RET}
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57 Similar, but select a buffer named @var{buffer} in another window
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58 (@code{switch-to-buffer-other-window}).
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59 @item M-x switch-to-other-buffer @var{n}
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60 Switch to the previous buffer.
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61 @end table
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62
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63 @kindex C-x 4 b
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64 @kindex C-x 5 b
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65 @findex switch-to-buffer-other-window
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66 @kindex C-x b
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67 @findex switch-to-buffer
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68 @findex switch-to-buffer-other-frame
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69 To select a buffer named @var{bufname}, type @kbd{C-x b @var{bufname}
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70 @key{RET}}. This is the command @code{switch-to-buffer} with argument
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71 @var{bufname}. You can use completion on an abbreviation for the buffer
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72 name you want (@pxref{Completion}). An empty argument to @kbd{C-x b}
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73 specifies the most recently selected buffer that is not displayed in any
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74 window.@refill
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75
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76 Most buffers are created when you visit files, or use Emacs commands
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77 that display text. You can also create a buffer explicitly by typing
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78 @kbd{C-x b @var{bufname} @key{RET}}, which creates a new, empty buffer
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79 that is not visiting any file, and selects it for editing. The new
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80 buffer's major mode is determined by the value of
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81 @code{default-major-mode} (@pxref{Major Modes}). Buffers not visiting
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82 files are usually used for making notes to yourself. If you try to save
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83 one, you are asked for the file name to use.
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84
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85 The function @code{switch-to-buffer-other-frame} is similar to
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86 @code{switch-to-buffer} except that it creates a new frame in which to
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87 display the selected buffer.
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88
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89 @findex switch-to-other-buffer
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90 Use @kbd{M-x switch-to-other-buffer} to visit the previous buffer. If
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91 you supply a positive integer @var{n}, the @var{n}th most recent buffer
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92 is displayed. If you supply an argument of 0, the current buffer is
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93 moved to the bottom of the buffer stack.
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94
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95 Note that you can also use @kbd{C-x C-f} and any other command for
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96 visiting a file to switch buffers. @xref{Visiting}.
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97
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98 @node List Buffers, Misc Buffer, Select Buffer, Buffers
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99 @section Listing Existing Buffers
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100
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101 @table @kbd
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102 @item C-x C-b
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103 List the existing buffers (@code{list-buffers}).
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104 @end table
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105
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106 @kindex C-x C-b
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107 @findex list-buffers
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108 To print a list of all existing buffers, type @kbd{C-x C-b}. Each
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109 line in the list shows one buffer's name, major mode, and visited file.
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110 A @samp{*} at the beginning of a line indicates the buffer has been
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111 ``modified''. If several buffers are modified, it may be time to save
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112 some with @kbd{C-x s} (@pxref{Saving}). A @samp{%} indicates a read-only
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113 buffer. A @samp{.} marks the selected buffer. Here is an example of a
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114 buffer list:@refill
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115
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116 @smallexample
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117 MR Buffer Size Mode File
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118 -- ------ ---- ---- ----
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119 .* emacs.tex 383402 Texinfo /u2/emacs/man/emacs.tex
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120 *Help* 1287 Fundamental
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121 files.el 23076 Emacs-Lisp /u2/emacs/lisp/files.el
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122 % RMAIL 64042 RMAIL /u/rms/RMAIL
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123 *% man 747 Dired /u2/emacs/man/
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124 net.emacs 343885 Fundamental /u/rms/net.emacs
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125 fileio.c 27691 C /u2/emacs/src/fileio.c
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126 NEWS 67340 Text /u2/emacs/etc/NEWS
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127 *scratch* 0 Lisp Interaction
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128 @end smallexample
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129
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130 @noindent
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131 Note that the buffer @samp{*Help*} was made by a help request; it is not
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132 visiting any file. The buffer @code{man} was made by Dired on the
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133 directory @file{/u2/emacs/man/}.
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134
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135 As you move the mouse over the @samp{*Buffer List*} buffer, the lines
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136 are highlighted. This visual cue indicates that clicking the right
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137 mouse button (@code{button3}) will pop up a menu of commands on the
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138 buffer represented by this line. This menu duplicates most of those
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139 commands which are bound to keys in the @samp{*Buffer List*} buffer.
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140
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141 @node Misc Buffer, Kill Buffer, List Buffers, Buffers
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142 @section Miscellaneous Buffer Operations
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143
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144 @table @kbd
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145 @item C-x C-q
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146 Toggle read-only status of buffer (@code{toggle-read-only}).
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147 @item M-x rename-buffer
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148 Change the name of the current buffer.
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149 @item M-x view-buffer
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150 Scroll through a buffer.
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151 @end table
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152
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153 @cindex read-only buffer
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154 @kindex C-x C-q
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155 @findex toggle-read-only
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156 @vindex buffer-read-only
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157 A buffer can be @dfn{read-only}, which means that commands to change
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158 its text are not allowed. Normally, read-only buffers are created by
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159 subsystems such as Dired and Rmail that have special commands to operate
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160 on the text. Emacs also creates a read-only buffer if you
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161 visit a file that is protected. To make changes in a read-only buffer,
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162 use the command @kbd{C-x C-q} (@code{toggle-read-only}). It makes a
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163 read-only buffer writable, and makes a writable buffer read-only. This
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164 works by setting the variable @code{buffer-read-only}, which has a local
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165 value in each buffer and makes a buffer read-only if its value is
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166 non-@code{nil}.
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167
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168 @findex rename-buffer
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169 @kbd{M-x rename-buffer} changes the name of the current buffer,
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170 prompting for the new name in the minibuffer. There is no default. If you
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171 specify a name that is used by a different buffer, an error is signalled and
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172 renaming is not done.
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173
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174 @findex view-buffer
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175 @kbd{M-x view-buffer} is similar to @kbd{M-x view-file} (@pxref{Misc
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176 File Ops}), but it examines an already existing Emacs buffer. View mode
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177 provides convenient commands for scrolling through the buffer but not
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178 for changing it. When you exit View mode, the resulting value of point
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179 remains in effect.
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180
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181 To copy text from one buffer to another, use the commands @kbd{M-x
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182 append-to-buffer} and @kbd{M-x insert-buffer}. @xref{Accumulating
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183 Text}.@refill
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184
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185 @node Kill Buffer, Several Buffers, Misc Buffer, Buffers
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186 @section Killing Buffers
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187
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188 After using Emacs for a while, you may accumulate a large number of
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189 buffers and may want to eliminate the ones you no
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190 longer need. There are several commands for doing this.
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191
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192 @c WideCommands
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193 @table @kbd
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194 @item C-x k
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195 Kill a buffer, specified by name (@code{kill-buffer}).
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196 @item M-x kill-some-buffers
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197 Offer to kill each buffer, one by one.
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198 @end table
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199
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200 @findex kill-buffer
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201 @findex kill-some-buffers
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202 @kindex C-x k
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203
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204 @kbd{C-x k} (@code{kill-buffer}) kills one buffer, whose name you
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205 specify in the minibuffer. If you type just @key{RET} in the
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206 minibuffer, the default, killing the current buffer, is used. If the
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207 current buffer is killed, the buffer that has been selected recently but
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208 does not appear in any window now is selected. If the buffer being
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209 killed contains unsaved changes, you are asked to confirm with @kbd{yes}
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210 before the buffer is killed.
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211
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212 The command @kbd{M-x kill-some-buffers} asks about each buffer, one by
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213 one. An answer of @kbd{y} means to kill the buffer. Killing the current
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214 buffer or a buffer containing unsaved changes selects a new buffer or asks
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215 for confirmation just like @code{kill-buffer}.
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216
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217 @node Several Buffers,, Kill Buffer, Buffers
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218 @section Operating on Several Buffers
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219 @cindex buffer menu
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220
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221 The @dfn{buffer-menu} facility is like a ``Dired for buffers''; it allows
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222 you to request operations on various Emacs buffers by editing a
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223 buffer containing a list of them. You can save buffers, kill them
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224 (here called @dfn{deleting} them, for consistency with Dired), or display
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225 them.
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226
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227 @table @kbd
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228 @item M-x buffer-menu
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229 Begin editing a buffer listing all Emacs buffers.
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230 @end table
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231
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232 @findex buffer-menu
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233 The command @code{buffer-menu} writes a list of all Emacs buffers into
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234 the buffer @samp{*Buffer List*}, and selects that buffer in Buffer Menu
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235 mode. The buffer is read-only. You can only change it using the special
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236 commands described in this section. Most of the commands are graphic
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237 characters. You can use Emacs cursor motion commands in the
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238 @samp{*Buffer List*} buffer. If the cursor is on a line describing a
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239 buffer, the following special commands apply to that buffer:
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240
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241 @table @kbd
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242 @item d
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243 Request to delete (kill) the buffer, then move down. A @samp{D} before
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244 the buffer name on a line indicates a deletion request. Requested
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245 deletions actually take place when you use the @kbd{x} command.
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246 @item k
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247 Synonym for @kbd{d}.
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248 @item C-d
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249 Like @kbd{d} but move up afterwards instead of down.
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250 @item s
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251 Request to save the buffer. An @samp{S} before the buffer name on a line
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252 indicates the request. Requested saves actually take place when you use
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253 the @kbd{x} command. You can request both saving and deletion for the
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254 same buffer.
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255 @item ~
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256 Mark buffer ``unmodified''. The command @kbd{~} does this
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257 immediately when typed.
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258 @item x
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259 Perform previously requested deletions and saves.
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260 @item u
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261 Remove any request made for the current line, and move down.
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262 @item @key{DEL}
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263 Move to previous line and remove any request made for that line.
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264 @end table
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265
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266 All commands that add or remove flags to request later operations
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267 also move down a line. They accept a numeric argument as a repeat count,
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268 unless otherwise specified.
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269
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270 There are also special commands to use the buffer list to select another
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271 buffer, and to specify one or more other buffers for display in additional
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272 windows.
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273
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274 @table @kbd
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275 @item 1
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276 Select the buffer in a full-frame window. This command takes effect
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277 immediately.
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278 @item 2
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279 Immediately set up two windows, with this buffer in one and the
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280 buffer selected before @samp{*Buffer List*} in the other.
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281 @item f
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282 Immediately select the buffer in place of the @samp{*Buffer List*} buffer.
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283 @item o
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284 Immediately select the buffer in another window as if by @kbd{C-x 4 b},
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285 leaving @samp{*Buffer List*} visible.
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286 @item q
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287 Immediately select this buffer, and display any buffers previously
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288 flagged with the @kbd{m} command in other windows. If there are no
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289 buffers flagged with @kbd{m}, this command is equivalent to @kbd{1}.
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290 @item m
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291 Flag this buffer to be displayed in another window if the @kbd{q}
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292 command is used. The request shows as a @samp{>} at the beginning of
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293 the line. The same buffer may not have both a delete request and a
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294 display request.
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295 @end table
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296
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297 Going back between a @code{buffer-menu} buffer and other Emacs buffers is
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298 easy. You can, for example, switch from the @samp{*Buffer List*}
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299 buffer to another Emacs buffer, and edit there. You can then reselect the
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300 @code{buffer-menu} buffer and perform operations already
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301 requested, or you can kill that buffer or pay no further attention to it.
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302 All that @code{buffer-menu} does directly is create and select a
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303 suitable buffer, and turn on Buffer Menu mode. All the other
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304 capabilities of the buffer menu are implemented by special commands
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305 provided in Buffer Menu mode.
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306
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307 The only difference between @code{buffer-menu} and @code{list-buffers} is
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308 that @code{buffer-menu} selects the @samp{*Buffer List*} buffer and
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309 @code{list-buffers} does not. If you run @code{list-buffers} (that is,
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310 type @kbd{C-x C-b}) and select the buffer list manually, you can use all
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311 the commands described here.
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