@c This is part of the Emacs manual. @c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 1999, 2000, @c 2001, 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. @c See file emacs.texi for copying conditions. @node Files, Buffers, Keyboard Macros, Top @chapter File Handling @cindex files The operating system stores data permanently in named @dfn{files}, so most of the text you edit with Emacs comes from a file and is ultimately stored in a file. To edit a file, you must tell Emacs to read the file and prepare a buffer containing a copy of the file's text. This is called @dfn{visiting} the file. Editing commands apply directly to text in the buffer; that is, to the copy inside Emacs. Your changes appear in the file itself only when you @dfn{save} the buffer back into the file. In addition to visiting and saving files, Emacs can delete, copy, rename, and append to files, keep multiple versions of them, and operate on file directories. @menu * File Names:: How to type and edit file-name arguments. * Visiting:: Visiting a file prepares Emacs to edit the file. * Saving:: Saving makes your changes permanent. * Reverting:: Reverting cancels all the changes not saved. @ifnottex * Autorevert:: Auto Reverting non-file buffers. @end ifnottex * Auto Save:: Auto Save periodically protects against loss of data. * File Aliases:: Handling multiple names for one file. * Version Control:: Version control systems (RCS, CVS and SCCS). * Directories:: Creating, deleting, and listing file directories. * Comparing Files:: Finding where two files differ. * Diff Mode:: Mode for editing file differences. * Misc File Ops:: Other things you can do on files. * Compressed Files:: Accessing compressed files. * File Archives:: Operating on tar, zip, jar etc. archive files. * Remote Files:: Accessing files on other sites. * Quoted File Names:: Quoting special characters in file names. * File Name Cache:: Completion against a list of files you often use. * File Conveniences:: Convenience Features for Finding Files. * Filesets:: Handling sets of files. @end menu @node File Names @section File Names @cindex file names Most Emacs commands that operate on a file require you to specify the file name. (Saving and reverting are exceptions; the buffer knows which file name to use for them.) You enter the file name using the minibuffer (@pxref{Minibuffer}). @dfn{Completion} is available (@pxref{Completion}) to make it easier to specify long file names. When completing file names, Emacs ignores those whose file-name extensions appear in the variable @code{completion-ignored-extensions}; see @ref{Completion Options}. For most operations, there is a @dfn{default file name} which is used if you type just @key{RET} to enter an empty argument. Normally the default file name is the name of the file visited in the current buffer; this makes it easy to operate on that file with any of the Emacs file commands. @vindex default-directory Each buffer has a default directory which is normally the same as the directory of the file visited in that buffer. When you enter a file name without a directory, the default directory is used. If you specify a directory in a relative fashion, with a name that does not start with a slash, it is interpreted with respect to the default directory. The default directory is kept in the variable @code{default-directory}, which has a separate value in every buffer. @findex cd @findex pwd The command @kbd{M-x pwd} displays the current buffer's default directory, and the command @kbd{M-x cd} sets it (to a value read using the minibuffer). A buffer's default directory changes only when the @code{cd} command is used. A file-visiting buffer's default directory is initialized to the directory of the file it visits. If you create a buffer with @kbd{C-x b}, its default directory is copied from that of the buffer that was current at the time. For example, if the default file name is @file{/u/rms/gnu/gnu.tasks} then the default directory is normally @file{/u/rms/gnu/}. If you type just @samp{foo}, which does not specify a directory, it is short for @file{/u/rms/gnu/foo}. @samp{../.login} would stand for @file{/u/rms/.login}. @samp{new/foo} would stand for the file name @file{/u/rms/gnu/new/foo}. @vindex insert-default-directory The default directory actually appears in the minibuffer when the minibuffer becomes active to read a file name. This serves two purposes: it @emph{shows} you what the default is, so that you can type a relative file name and know with certainty what it will mean, and it allows you to @emph{edit} the default to specify a different directory. This insertion of the default directory is inhibited if the variable @code{insert-default-directory} is set to @code{nil}. Note that it is legitimate to type an absolute file name after you enter the minibuffer, ignoring the presence of the default directory name as part of the text. The final minibuffer contents may look invalid, but that is not so. For example, if the minibuffer starts out with @samp{/usr/tmp/} and you add @samp{/x1/rms/foo}, you get @samp{/usr/tmp//x1/rms/foo}; but Emacs ignores everything through the first slash in the double slash; the result is @samp{/x1/rms/foo}. @xref{Minibuffer File}. @cindex home directory shorthand You can use @file{~/} in a file name to mean your home directory, or @file{~@var{user-id}/} to mean the home directory of a user whose login name is @code{user-id}@footnote{ On MS-Windows and MS-DOS systems, where a user doesn't have a home directory, Emacs replaces @file{~/} with the value of the environment variable @code{HOME}; see @ref{General Variables}. On these systems, the @file{~@var{user-id}/} construct is supported only for the current user, i.e., only if @var{user-id} is the current user's login name.}. @cindex environment variables in file names @cindex expansion of environment variables @cindex @code{$} in file names @anchor{File Names with $}@samp{$} in a file name is used to substitute an environment variable. The environment variable name consists of all the alphanumeric characters after the @samp{$}; alternatively, it can be enclosed in braces after the @samp{$}. For example, if you have used the shell command @command{export FOO=rms/hacks} to set up an environment variable named @env{FOO}, then you can use @file{/u/$FOO/test.c} or @file{/u/$@{FOO@}/test.c} as an abbreviation for @file{/u/rms/hacks/test.c}. If the environment variable is not defined, no substitution occurs: @file{/u/$notdefined} stands for itself (assuming the environment variable @env{notdefined} is not defined). Note that shell commands to set environment variables affect Emacs only when done before Emacs is started. To access a file with @samp{$} in its name, if the @samp{$} causes expansion, type @samp{$$}. This pair is converted to a single @samp{$} at the same time as variable substitution is performed for a single @samp{$}. Alternatively, quote the whole file name with @samp{/:} (@pxref{Quoted File Names}). File names which begin with a literal @samp{~} should also be quoted with @samp{/:}. @findex substitute-in-file-name The Lisp function that performs the @samp{$}-substitution is called @code{substitute-in-file-name}. The substitution is performed only on file names read as such using the minibuffer. You can include non-@acronym{ASCII} characters in file names if you set the variable @code{file-name-coding-system} to a non-@code{nil} value. @xref{File Name Coding}. @node Visiting @section Visiting Files @cindex visiting files @cindex open file @table @kbd @item C-x C-f Visit a file (@code{find-file}). @item C-x C-r Visit a file for viewing, without allowing changes to it (@code{find-file-read-only}). @item C-x C-v Visit a different file instead of the one visited last (@code{find-alternate-file}). @item C-x 4 f Visit a file, in another window (@code{find-file-other-window}). Don't alter what is displayed in the selected window. @item C-x 5 f Visit a file, in a new frame (@code{find-file-other-frame}). Don't alter what is displayed in the selected frame. @item M-x find-file-literally Visit a file with no conversion of the contents. @end table @cindex files, visiting and saving @cindex saving files @dfn{Visiting} a file means reading its contents into an Emacs buffer so you can edit them. Emacs makes a new buffer for each file that you visit. We often say that this buffer ``is visiting'' that file, or that the buffer's ``visited file'' is that file. Emacs constructs the buffer name from the file name by throwing away the directory, keeping just the name proper. For example, a file named @file{/usr/rms/emacs.tex} would get a buffer named @samp{emacs.tex}. If there is already a buffer with that name, Emacs constructs a unique name---the normal method is to append @samp{<2>}, @samp{<3>}, and so on, but you can select other methods (@pxref{Uniquify}). Each window's mode line shows the name of the buffer that is being displayed in that window, so you can always tell what buffer you are editing. The changes you make with editing commands are made in the Emacs buffer. They do not take effect in the file that you visited, or any permanent place, until you @dfn{save} the buffer. Saving the buffer means that Emacs writes the current contents of the buffer into its visited file. @xref{Saving}. @cindex modified (buffer) If a buffer contains changes that have not been saved, we say the buffer is @dfn{modified}. This is important because it implies that some changes will be lost if the buffer is not saved. The mode line displays two stars near the left margin to indicate that the buffer is modified. @kindex C-x C-f @findex find-file To visit a file, use the command @kbd{C-x C-f} (@code{find-file}). Follow the command with the name of the file you wish to visit, terminated by a @key{RET}. The file name is read using the minibuffer (@pxref{Minibuffer}), with defaulting and completion in the standard manner (@pxref{File Names}). While in the minibuffer, you can abort @kbd{C-x C-f} by typing @kbd{C-g}. File-name completion ignores certain file names; for more about this, see @ref{Completion Options}. Your confirmation that @kbd{C-x C-f} has completed successfully is the appearance of new text on the screen and a new buffer name in the mode line. If the specified file does not exist and you could not create it, or exists but you can't read it, then you get an error, with an error message displayed in the echo area. If you visit a file that is already in Emacs, @kbd{C-x C-f} does not make another copy. It selects the existing buffer containing that file. However, before doing so, it checks whether the file itself has changed since you visited or saved it last. If the file has changed, Emacs offers to reread it. @vindex large-file-warning-threshold @cindex maximum buffer size exceeded, error message If you try to visit a file larger than @code{large-file-warning-threshold} (the default is 10000000, which is about 10 megabytes), Emacs will ask you for confirmation first. You can answer @kbd{y} to proceed with visiting the file. Note, however, that Emacs cannot visit files that are larger than the maximum Emacs buffer size, which is around 256 megabytes on 32-bit machines (@pxref{Buffers}). If you try, Emacs will display an error message saying that the maximum buffer size has been exceeded. @cindex file selection dialog On graphical displays there are two additional methods for visiting files. Firstly, when Emacs is built with a suitable GUI toolkit, commands invoked with the mouse (by clicking on the menu bar or tool bar) use the toolkit's standard File Selection dialog instead of prompting for the file name in the minibuffer. On Unix and GNU/Linux platforms, Emacs does that when built with GTK, LessTif, and Motif toolkits; on MS-Windows and Mac, the GUI version does that by default. For information on how to customize this, see @ref{Dialog Boxes}. Secondly, Emacs supports ``drag and drop''; dropping a file into an ordinary Emacs window visits the file using that window. However, dropping a file into a window displaying a Dired buffer moves or copies the file into the displayed directory. For details, see @ref{Drag and Drop}, and @ref{Misc Dired Features}. @cindex creating files What if you want to create a new file? Just visit it. Emacs displays @samp{(New file)} in the echo area, but in other respects behaves as if you had visited an existing empty file. If you make any changes and save them, the file is created. Emacs recognizes from the contents of a file which end-of-line convention it uses to separate lines---newline (used on GNU/Linux and on Unix), carriage-return linefeed (used on Microsoft systems), or just carriage-return (used on the Macintosh)---and automatically converts the contents to the normal Emacs convention, which is that the newline character separates lines. This is a part of the general feature of coding system conversion (@pxref{Coding Systems}), and makes it possible to edit files imported from different operating systems with equal convenience. If you change the text and save the file, Emacs performs the inverse conversion, changing newlines back into carriage-return linefeed or just carriage-return if appropriate. @vindex find-file-run-dired If the file you specify is actually a directory, @kbd{C-x C-f} invokes Dired, the Emacs directory browser, so that you can ``edit'' the contents of the directory (@pxref{Dired}). Dired is a convenient way to view, delete, or operate on the files in the directory. However, if the variable @code{find-file-run-dired} is @code{nil}, then it is an error to try to visit a directory. Files which are actually collections of other files, or @dfn{file archives}, are visited in special modes which invoke a Dired-like environment to allow operations on archive members. @xref{File Archives}, for more about these features. @cindex wildcard characters in file names @vindex find-file-wildcards If the file name you specify contains shell-style wildcard characters, Emacs visits all the files that match it. (On case-insensitive filesystems, Emacs matches the wildcards disregarding the letter case.) Wildcards include @samp{?}, @samp{*}, and @samp{[@dots{}]} sequences. To enter the wild card @samp{?} in a file name in the minibuffer, you need to type @kbd{C-q ?}. @xref{Quoted File Names}, for information on how to visit a file whose name actually contains wildcard characters. You can disable the wildcard feature by customizing @code{find-file-wildcards}. If you visit a file that the operating system won't let you modify, or that is marked read-only, Emacs makes the buffer read-only too, so that you won't go ahead and make changes that you'll have trouble saving afterward. You can make the buffer writable with @kbd{C-x C-q} (@code{toggle-read-only}). @xref{Misc Buffer}. @kindex C-x C-r @findex find-file-read-only If you want to visit a file as read-only in order to protect yourself from entering changes accidentally, visit it with the command @kbd{C-x C-r} (@code{find-file-read-only}) instead of @kbd{C-x C-f}. @kindex C-x C-v @findex find-alternate-file If you visit a nonexistent file unintentionally (because you typed the wrong file name), use the @kbd{C-x C-v} command (@code{find-alternate-file}) to visit the file you really wanted. @kbd{C-x C-v} is similar to @kbd{C-x C-f}, but it kills the current buffer (after first offering to save it if it is modified). When @kbd{C-x C-v} reads the file name to visit, it inserts the entire default file name in the buffer, with point just after the directory part; this is convenient if you made a slight error in typing the name. @kindex C-x 4 f @findex find-file-other-window @kbd{C-x 4 f} (@code{find-file-other-window}) is like @kbd{C-x C-f} except that the buffer containing the specified file is selected in another window. The window that was selected before @kbd{C-x 4 f} continues to show the same buffer it was already showing. If this command is used when only one window is being displayed, that window is split in two, with one window showing the same buffer as before, and the other one showing the newly requested file. @xref{Windows}. @kindex C-x 5 f @findex find-file-other-frame @kbd{C-x 5 f} (@code{find-file-other-frame}) is similar, but opens a new frame, or makes visible any existing frame showing the file you seek. This feature is available only when you are using a window system. @xref{Frames}. @findex find-file-literally If you wish to edit a file as a sequence of @acronym{ASCII} characters with no special encoding or conversion, use the @kbd{M-x find-file-literally} command. It visits a file, like @kbd{C-x C-f}, but does not do format conversion (@pxref{Formatted Text}), character code conversion (@pxref{Coding Systems}), or automatic uncompression (@pxref{Compressed Files}), and does not add a final newline because of @code{require-final-newline}. If you already have visited the same file in the usual (non-literal) manner, this command asks you whether to visit it literally instead. @vindex find-file-hook @vindex find-file-not-found-functions Two special hook variables allow extensions to modify the operation of visiting files. Visiting a file that does not exist runs the functions in the list @code{find-file-not-found-functions}; this variable holds a list of functions, and the functions are called one by one (with no arguments) until one of them returns non-@code{nil}. This is not a normal hook, and the name ends in @samp{-functions} rather than @samp{-hook} to indicate that fact. Successful visiting of any file, whether existing or not, calls the functions in the list @code{find-file-hook}, with no arguments. This variable is a normal hook. In the case of a nonexistent file, the @code{find-file-not-found-functions} are run first. @xref{Hooks}. There are several ways to specify automatically the major mode for editing the file (@pxref{Choosing Modes}), and to specify local variables defined for that file (@pxref{File Variables}). @node Saving @section Saving Files @dfn{Saving} a buffer in Emacs means writing its contents back into the file that was visited in the buffer. @menu * Save Commands:: Commands for saving files. * Backup:: How Emacs saves the old version of your file. * Customize Save:: Customizing the saving of files. * Interlocking:: How Emacs protects against simultaneous editing of one file by two users. * Shadowing: File Shadowing. Copying files to "shadows" automatically. * Time Stamps:: Emacs can update time stamps on saved files. @end menu @node Save Commands @subsection Commands for Saving Files These are the commands that relate to saving and writing files. @table @kbd @item C-x C-s Save the current buffer in its visited file on disk (@code{save-buffer}). @item C-x s Save any or all buffers in their visited files (@code{save-some-buffers}). @item M-~ Forget that the current buffer has been changed (@code{not-modified}). With prefix argument (@kbd{C-u}), mark the current buffer as changed. @item C-x C-w Save the current buffer with a specified file name (@code{write-file}). @item M-x set-visited-file-name Change the file name under which the current buffer will be saved. @end table @kindex C-x C-s @findex save-buffer When you wish to save the file and make your changes permanent, type @kbd{C-x C-s} (@code{save-buffer}). After saving is finished, @kbd{C-x C-s} displays a message like this: @example Wrote /u/rms/gnu/gnu.tasks @end example @noindent If the selected buffer is not modified (no changes have been made in it since the buffer was created or last saved), saving is not really done, because it would have no effect. Instead, @kbd{C-x C-s} displays a message like this in the echo area: @example (No changes need to be saved) @end example @kindex C-x s @findex save-some-buffers The command @kbd{C-x s} (@code{save-some-buffers}) offers to save any or all modified buffers. It asks you what to do with each buffer. The possible responses are analogous to those of @code{query-replace}: @table @kbd @item y Save this buffer and ask about the rest of the buffers. @item n Don't save this buffer, but ask about the rest of the buffers. @item ! Save this buffer and all the rest with no more questions. @c following generates acceptable underfull hbox @item @key{RET} Terminate @code{save-some-buffers} without any more saving. @item . Save this buffer, then exit @code{save-some-buffers} without even asking about other buffers. @item C-r View the buffer that you are currently being asked about. When you exit View mode, you get back to @code{save-some-buffers}, which asks the question again. @item d Diff the buffer against its corresponding file, so you can see what changes you would be saving. @item C-h Display a help message about these options. @end table @kbd{C-x C-c}, the key sequence to exit Emacs, invokes @code{save-some-buffers} and therefore asks the same questions. @kindex M-~ @findex not-modified If you have changed a buffer but you do not want to save the changes, you should take some action to prevent it. Otherwise, each time you use @kbd{C-x s} or @kbd{C-x C-c}, you are liable to save this buffer by mistake. One thing you can do is type @kbd{M-~} (@code{not-modified}), which clears out the indication that the buffer is modified. If you do this, none of the save commands will believe that the buffer needs to be saved. (@samp{~} is often used as a mathematical symbol for `not'; thus @kbd{M-~} is `not', metafied.) You could also use @code{set-visited-file-name} (see below) to mark the buffer as visiting a different file name, one which is not in use for anything important. Alternatively, you can cancel all the changes made since the file was visited or saved, by reading the text from the file again. This is called @dfn{reverting}. @xref{Reverting}. (You could also undo all the changes by repeating the undo command @kbd{C-x u} until you have undone all the changes; but reverting is easier.) You can also kill the buffer. @findex set-visited-file-name @kbd{M-x set-visited-file-name} alters the name of the file that the current buffer is visiting. It reads the new file name using the minibuffer. Then it marks the buffer as visiting that file name, and changes the buffer name correspondingly. @code{set-visited-file-name} does not save the buffer in the newly visited file; it just alters the records inside Emacs in case you do save later. It also marks the buffer as ``modified'' so that @kbd{C-x C-s} in that buffer @emph{will} save. @kindex C-x C-w @findex write-file If you wish to mark the buffer as visiting a different file and save it right away, use @kbd{C-x C-w} (@code{write-file}). It is equivalent to @code{set-visited-file-name} followed by @kbd{C-x C-s} (except that @kbd{C-x C-w} asks for confirmation if the file exists). @kbd{C-x C-s} used on a buffer that is not visiting a file has the same effect as @kbd{C-x C-w}; that is, it reads a file name, marks the buffer as visiting that file, and saves it there. The default file name in a buffer that is not visiting a file is made by combining the buffer name with the buffer's default directory (@pxref{File Names}). If the new file name implies a major mode, then @kbd{C-x C-w} switches to that major mode, in most cases. The command @code{set-visited-file-name} also does this. @xref{Choosing Modes}. If Emacs is about to save a file and sees that the date of the latest version on disk does not match what Emacs last read or wrote, Emacs notifies you of this fact, because it probably indicates a problem caused by simultaneous editing and requires your immediate attention. @xref{Interlocking,, Simultaneous Editing}. @node Backup @subsection Backup Files @cindex backup file @vindex make-backup-files @vindex vc-make-backup-files On most operating systems, rewriting a file automatically destroys all record of what the file used to contain. Thus, saving a file from Emacs throws away the old contents of the file---or it would, except that Emacs carefully copies the old contents to another file, called the @dfn{backup} file, before actually saving. For most files, the variable @code{make-backup-files} determines whether to make backup files. On most operating systems, its default value is @code{t}, so that Emacs does write backup files. For files managed by a version control system (@pxref{Version Control}), the variable @code{vc-make-backup-files} determines whether to make backup files. By default it is @code{nil}, since backup files are redundant when you store all the previous versions in a version control system. @iftex @xref{General VC Options,,,emacs-xtra, Specialized Emacs Features}. @end iftex @ifnottex @xref{General VC Options}. @end ifnottex At your option, Emacs can keep either a single backup for each file, or make a series of numbered backup files for each file that you edit. @vindex backup-enable-predicate @vindex temporary-file-directory @vindex small-temporary-file-directory The default value of the @code{backup-enable-predicate} variable prevents backup files being written for files in the directories used for temporary files, specified by @code{temporary-file-directory} or @code{small-temporary-file-directory}. Emacs makes a backup for a file only the first time the file is saved from one buffer. No matter how many times you save a file, its backup file continues to contain the contents from before the file was visited. Normally this means that the backup file contains the contents from before the current editing session; however, if you kill the buffer and then visit the file again, a new backup file will be made by the next save. You can also explicitly request making another backup file from a buffer even though it has already been saved at least once. If you save the buffer with @kbd{C-u C-x C-s}, the version thus saved will be made into a backup file if you save the buffer again. @kbd{C-u C-u C-x C-s} saves the buffer, but first makes the previous file contents into a new backup file. @kbd{C-u C-u C-u C-x C-s} does both things: it makes a backup from the previous contents, and arranges to make another from the newly saved contents if you save again. @menu * One or Many: Numbered Backups. Whether to make one backup file or many. * Names: Backup Names. How backup files are named. * Deletion: Backup Deletion. Emacs deletes excess numbered backups. * Copying: Backup Copying. Backups can be made by copying or renaming. @end menu @node Numbered Backups @subsubsection Numbered Backups @vindex version-control The choice of single backup file or multiple numbered backup files is controlled by the variable @code{version-control}. Its possible values are: @table @code @item t Make numbered backups. @item nil Make numbered backups for files that have numbered backups already. Otherwise, make single backups. @item never Never make numbered backups; always make single backups. @end table @noindent The usual way to set this variable is globally, through your @file{.emacs} file or the customization buffer. However, you can set @code{version-control} locally in an individual buffer to control the making of backups for that buffer's file. For example, Rmail mode locally sets @code{version-control} to @code{never} to make sure that there is only one backup for an Rmail file. @xref{Locals}. @cindex @env{VERSION_CONTROL} environment variable If you set the environment variable @env{VERSION_CONTROL}, to tell various GNU utilities what to do with backup files, Emacs also obeys the environment variable by setting the Lisp variable @code{version-control} accordingly at startup. If the environment variable's value is @samp{t} or @samp{numbered}, then @code{version-control} becomes @code{t}; if the value is @samp{nil} or @samp{existing}, then @code{version-control} becomes @code{nil}; if it is @samp{never} or @samp{simple}, then @code{version-control} becomes @code{never}. @node Backup Names @subsubsection Single or Numbered Backups When Emacs makes a single backup file, its name is normally constructed by appending @samp{~} to the file name being edited; thus, the backup file for @file{eval.c} would be @file{eval.c~}. @vindex make-backup-file-name-function @vindex backup-directory-alist You can change this behavior by defining the variable @code{make-backup-file-name-function} to a suitable function. Alternatively you can customize the variable @code{backup-directory-alist} to specify that files matching certain patterns should be backed up in specific directories. A typical use is to add an element @code{("." . @var{dir})} to make all backups in the directory with absolute name @var{dir}; Emacs modifies the backup file names to avoid clashes between files with the same names originating in different directories. Alternatively, adding, say, @code{("." . ".~")} would make backups in the invisible subdirectory @file{.~} of the original file's directory. Emacs creates the directory, if necessary, to make the backup. If access control stops Emacs from writing backup files under the usual names, it writes the backup file as @file{%backup%~} in your home directory. Only one such file can exist, so only the most recently made such backup is available. If you choose to have a series of numbered backup files, backup file names contain @samp{.~}, the number, and another @samp{~} after the original file name. Thus, the backup files of @file{eval.c} would be called @file{eval.c.~1~}, @file{eval.c.~2~}, and so on, all the way through names like @file{eval.c.~259~} and beyond. The variable @code{backup-directory-alist} applies to numbered backups just as usual. @node Backup Deletion @subsubsection Automatic Deletion of Backups To prevent excessive consumption of disk space, Emacs can delete numbered backup versions automatically. Generally Emacs keeps the first few backups and the latest few backups, deleting any in between. This happens every time a new backup is made. @vindex kept-old-versions @vindex kept-new-versions The two variables @code{kept-old-versions} and @code{kept-new-versions} control this deletion. Their values are, respectively, the number of oldest (lowest-numbered) backups to keep and the number of newest (highest-numbered) ones to keep, each time a new backup is made. The backups in the middle (excluding those oldest and newest) are the excess middle versions---those backups are deleted. These variables' values are used when it is time to delete excess versions, just after a new backup version is made; the newly made backup is included in the count in @code{kept-new-versions}. By default, both variables are 2. @vindex delete-old-versions If @code{delete-old-versions} is @code{t}, Emacs deletes the excess backup files silently. If it is @code{nil}, the default, Emacs asks you whether it should delete the excess backup versions. If it has any other value, then Emacs never automatically deletes backups. Dired's @kbd{.} (Period) command can also be used to delete old versions. @xref{Dired Deletion}. @node Backup Copying @subsubsection Copying vs.@: Renaming Backup files can be made by copying the old file or by renaming it. This makes a difference when the old file has multiple names (hard links). If the old file is renamed into the backup file, then the alternate names become names for the backup file. If the old file is copied instead, then the alternate names remain names for the file that you are editing, and the contents accessed by those names will be the new contents. The method of making a backup file may also affect the file's owner and group. If copying is used, these do not change. If renaming is used, you become the file's owner, and the file's group becomes the default (different operating systems have different defaults for the group). Having the owner change is usually a good idea, because then the owner always shows who last edited the file. Also, the owners of the backups show who produced those versions. Occasionally there is a file whose owner should not change; it is a good idea for such files to contain local variable lists to set @code{backup-by-copying-when-mismatch} locally (@pxref{File Variables}). @vindex backup-by-copying @vindex backup-by-copying-when-linked @vindex backup-by-copying-when-mismatch @vindex backup-by-copying-when-privileged-mismatch @cindex file ownership, and backup @cindex backup, and user-id The choice of renaming or copying is controlled by four variables. Renaming is the default choice. If the variable @code{backup-by-copying} is non-@code{nil}, copying is used. Otherwise, if the variable @code{backup-by-copying-when-linked} is non-@code{nil}, then copying is used for files that have multiple names, but renaming may still be used when the file being edited has only one name. If the variable @code{backup-by-copying-when-mismatch} is non-@code{nil}, then copying is used if renaming would cause the file's owner or group to change. @code{backup-by-copying-when-mismatch} is @code{t} by default if you start Emacs as the superuser. The fourth variable, @code{backup-by-copying-when-privileged-mismatch}, gives the highest numeric user-id for which @code{backup-by-copying-when-mismatch} will be forced on. This is useful when low-numbered user-ids are assigned to special system users, such as @code{root}, @code{bin}, @code{daemon}, etc., which must maintain ownership of files. When a file is managed with a version control system (@pxref{Version Control}), Emacs does not normally make backups in the usual way for that file. But check-in and check-out are similar in some ways to making backups. One unfortunate similarity is that these operations typically break hard links, disconnecting the file name you visited from any alternate names for the same file. This has nothing to do with Emacs---the version control system does it. @node Customize Save @subsection Customizing Saving of Files @vindex require-final-newline If the value of the variable @code{require-final-newline} is @code{t}, saving or writing a file silently puts a newline at the end if there isn't already one there. If the value is @code{visit}, Emacs adds a newline at the end of any file that doesn't have one, just after it visits the file. (This marks the buffer as modified, and you can undo it.) If the value is @code{visit-save}, that means to add newlines both on visiting and on saving. If the value is @code{nil}, Emacs leaves the end of the file unchanged; if it's neither @code{nil} nor @code{t}, Emacs asks you whether to add a newline. The default is @code{nil}. @vindex mode-require-final-newline Many major modes are designed for specific kinds of files that are always supposed to end in newlines. These major modes set the variable @code{require-final-newline} according to @code{mode-require-final-newline}. By setting the latter variable, you can control how these modes handle final newlines. @vindex write-region-inhibit-fsync When Emacs saves a file, it invokes the @code{fsync} system call to force the data immediately out to disk. This is important for safety if the system crashes or in case of power outage. However, it can be disruptive on laptops using power saving, because it requires the disk to spin up each time you save a file. Setting @code{write-region-inhibit-fsync} to a non-@code{nil} value disables this synchronization. Be careful---this means increased risk of data loss. @node Interlocking @subsection Protection against Simultaneous Editing @cindex file dates @cindex simultaneous editing Simultaneous editing occurs when two users visit the same file, both make changes, and then both save them. If nobody were informed that this was happening, whichever user saved first would later find that his changes were lost. On some systems, Emacs notices immediately when the second user starts to change the file, and issues an immediate warning. On all systems, Emacs checks when you save the file, and warns if you are about to overwrite another user's changes. You can prevent loss of the other user's work by taking the proper corrective action instead of saving the file. @findex ask-user-about-lock @cindex locking files When you make the first modification in an Emacs buffer that is visiting a file, Emacs records that the file is @dfn{locked} by you. (It does this by creating a symbolic link in the same directory with a different name.) Emacs removes the lock when you save the changes. The idea is that the file is locked whenever an Emacs buffer visiting it has unsaved changes. @cindex collision If you begin to modify the buffer while the visited file is locked by someone else, this constitutes a @dfn{collision}. When Emacs detects a collision, it asks you what to do, by calling the Lisp function @code{ask-user-about-lock}. You can redefine this function for the sake of customization. The standard definition of this function asks you a question and accepts three possible answers: @table @kbd @item s Steal the lock. Whoever was already changing the file loses the lock, and you gain the lock. @item p Proceed. Go ahead and edit the file despite its being locked by someone else. @item q Quit. This causes an error (@code{file-locked}), and the buffer contents remain unchanged---the modification you were trying to make does not actually take place. @end table Note that locking works on the basis of a file name; if a file has multiple names, Emacs does not realize that the two names are the same file and cannot prevent two users from editing it simultaneously under different names. However, basing locking on names means that Emacs can interlock the editing of new files that will not really exist until they are saved. Some systems are not configured to allow Emacs to make locks, and there are cases where lock files cannot be written. In these cases, Emacs cannot detect trouble in advance, but it still can detect the collision when you try to save a file and overwrite someone else's changes. If Emacs or the operating system crashes, this may leave behind lock files which are stale, so you may occasionally get warnings about spurious collisions. When you determine that the collision is spurious, just use @kbd{p} to tell Emacs to go ahead anyway. Every time Emacs saves a buffer, it first checks the last-modification date of the existing file on disk to verify that it has not changed since the file was last visited or saved. If the date does not match, it implies that changes were made in the file in some other way, and these changes are about to be lost if Emacs actually does save. To prevent this, Emacs displays a warning message and asks for confirmation before saving. Occasionally you will know why the file was changed and know that it does not matter; then you can answer @kbd{yes} and proceed. Otherwise, you should cancel the save with @kbd{C-g} and investigate the situation. The first thing you should do when notified that simultaneous editing has already taken place is to list the directory with @kbd{C-u C-x C-d} (@pxref{Directories}). This shows the file's current author. You should attempt to contact him to warn him not to continue editing. Often the next step is to save the contents of your Emacs buffer under a different name, and use @code{diff} to compare the two files.@refill @node File Shadowing @subsection Shadowing Files @cindex shadow files @cindex file shadows @findex shadow-initialize @table @kbd @item M-x shadow-initialize Set up file shadowing. @item M-x shadow-define-literal-group Declare a single file to be shared between sites. @item M-x shadow-define-regexp-group Make all files that match each of a group of files be shared between hosts. @item M-x shadow-define-cluster @key{RET} @var{name} @key{RET} Define a shadow file cluster @var{name}. @item M-x shadow-copy-files Copy all pending shadow files. @item M-x shadow-cancel Cancel the instruction to shadow some files. @end table You can arrange to keep identical @dfn{shadow} copies of certain files in more than one place---possibly on different machines. To do this, first you must set up a @dfn{shadow file group}, which is a set of identically-named files shared between a list of sites. The file group is permanent and applies to further Emacs sessions as well as the current one. Once the group is set up, every time you exit Emacs, it will copy the file you edited to the other files in its group. You can also do the copying without exiting Emacs, by typing @kbd{M-x shadow-copy-files}. To set up a shadow file group, use @kbd{M-x shadow-define-literal-group} or @kbd{M-x shadow-define-regexp-group}. See their documentation strings for further information. Before copying a file to its shadows, Emacs asks for confirmation. You can answer ``no'' to bypass copying of this file, this time. If you want to cancel the shadowing permanently for a certain file, use @kbd{M-x shadow-cancel} to eliminate or change the shadow file group. A @dfn{shadow cluster} is a group of hosts that share directories, so that copying to or from one of them is sufficient to update the file on all of them. Each shadow cluster has a name, and specifies the network address of a primary host (the one we copy files to), and a regular expression that matches the host names of all the other hosts in the cluster. You can define a shadow cluster with @kbd{M-x shadow-define-cluster}. @node Time Stamps @subsection Updating Time Stamps Automatically @cindex time stamps @cindex modification dates @cindex locale, date format You can arrange to put a time stamp in a file, so that it will be updated automatically each time you edit and save the file. The time stamp has to be in the first eight lines of the file, and you should insert it like this: @example Time-stamp: <> @end example @noindent or like this: @example Time-stamp: " " @end example @findex time-stamp Then add the hook function @code{time-stamp} to the hook @code{before-save-hook}; that hook function will automatically update the time stamp, inserting the current date and time when you save the file. You can also use the command @kbd{M-x time-stamp} to update the time stamp manually. For other customizations, see the Custom group @code{time-stamp}. Note that non-numeric fields in the time stamp are formatted according to your locale setting (@pxref{Environment}). @node Reverting @section Reverting a Buffer @findex revert-buffer @cindex drastic changes @cindex reread a file If you have made extensive changes to a file and then change your mind about them, you can get rid of them by reading in the previous version of the file. To do this, use @kbd{M-x revert-buffer}, which operates on the current buffer. Since reverting a buffer unintentionally could lose a lot of work, you must confirm this command with @kbd{yes}. @code{revert-buffer} tries to position point in such a way that, if the file was edited only slightly, you will be at approximately the same piece of text after reverting as before. However, if you have made drastic changes, point may wind up in a totally different piece of text. Reverting marks the buffer as ``not modified'' until another change is made. Some kinds of buffers whose contents reflect data bases other than files, such as Dired buffers, can also be reverted. For them, reverting means recalculating their contents from the appropriate data base. Buffers created explicitly with @kbd{C-x b} cannot be reverted; @code{revert-buffer} reports an error when asked to do so. @vindex revert-without-query When you edit a file that changes automatically and frequently---for example, a log of output from a process that continues to run---it may be useful for Emacs to revert the file without querying you, whenever you visit the file again with @kbd{C-x C-f}. To request this behavior, set the variable @code{revert-without-query} to a list of regular expressions. When a file name matches one of these regular expressions, @code{find-file} and @code{revert-buffer} will revert it automatically if it has changed---provided the buffer itself is not modified. (If you have edited the text, it would be wrong to discard your changes.) @cindex Global Auto-Revert mode @cindex mode, Global Auto-Revert @cindex Auto-Revert mode @cindex mode, Auto-Revert @findex global-auto-revert-mode @findex auto-revert-mode @findex auto-revert-tail-mode You may find it useful to have Emacs revert files automatically when they change. Three minor modes are available to do this. @kbd{M-x global-auto-revert-mode} enables Global Auto-Revert mode, which periodically checks all file buffers and reverts when the corresponding file has changed. @kbd{M-x auto-revert-mode} enables a local version, Auto-Revert mode, which applies only to the current buffer. You can use Auto-Revert mode to ``tail'' a file such as a system log, so that changes made to that file by other programs are continuously displayed. To do this, just move the point to the end of the buffer, and it will stay there as the file contents change. However, if you are sure that the file will only change by growing at the end, use Auto-Revert Tail mode instead (@code{auto-revert-tail-mode}). It is more efficient for this. @vindex auto-revert-interval The variable @code{auto-revert-interval} controls how often to check for a changed file. Since checking a remote file is too slow, these modes do not check or revert remote files. @xref{VC Mode Line}, for Auto Revert peculiarities in buffers that visit files under version control. @ifnottex @include arevert-xtra.texi @end ifnottex @node Auto Save @section Auto-Saving: Protection Against Disasters @cindex Auto Save mode @cindex mode, Auto Save @cindex crashes Emacs saves all the visited files from time to time (based on counting your keystrokes) without being asked. This is called @dfn{auto-saving}. It prevents you from losing more than a limited amount of work if the system crashes. When Emacs determines that it is time for auto-saving, it considers each buffer, and each is auto-saved if auto-saving is enabled for it and it has been changed since the last time it was auto-saved. The message @samp{Auto-saving...} is displayed in the echo area during auto-saving, if any files are actually auto-saved. Errors occurring during auto-saving are caught so that they do not interfere with the execution of commands you have been typing. @menu * Files: Auto Save Files. The file where auto-saved changes are actually made until you save the file. * Control: Auto Save Control. Controlling when and how often to auto-save. * Recover:: Recovering text from auto-save files. @end menu @node Auto Save Files @subsection Auto-Save Files Auto-saving does not normally save in the files that you visited, because it can be very undesirable to save a program that is in an inconsistent state when you have made half of a planned change. Instead, auto-saving is done in a different file called the @dfn{auto-save file}, and the visited file is changed only when you request saving explicitly (such as with @kbd{C-x C-s}). Normally, the auto-save file name is made by appending @samp{#} to the front and rear of the visited file name. Thus, a buffer visiting file @file{foo.c} is auto-saved in a file @file{#foo.c#}. Most buffers that are not visiting files are auto-saved only if you request it explicitly; when they are auto-saved, the auto-save file name is made by appending @samp{#} to the front and rear of buffer name, then adding digits and letters at the end for uniqueness. For example, the @samp{*mail*} buffer in which you compose messages to be sent might be auto-saved in a file named @file{#*mail*#704juu}. Auto-save file names are made this way unless you reprogram parts of Emacs to do something different (the functions @code{make-auto-save-file-name} and @code{auto-save-file-name-p}). The file name to be used for auto-saving in a buffer is calculated when auto-saving is turned on in that buffer. @cindex auto-save for remote files @vindex auto-save-file-name-transforms The variable @code{auto-save-file-name-transforms} allows a degree of control over the auto-save file name. It lets you specify a series of regular expressions and replacements to transform the auto save file name. The default value puts the auto-save files for remote files (@pxref{Remote Files}) into the temporary file directory on the local machine. When you delete a substantial part of the text in a large buffer, auto save turns off temporarily in that buffer. This is because if you deleted the text unintentionally, you might find the auto-save file more useful if it contains the deleted text. To reenable auto-saving after this happens, save the buffer with @kbd{C-x C-s}, or use @kbd{C-u 1 M-x auto-save-mode}. @vindex auto-save-visited-file-name If you want auto-saving to be done in the visited file rather than in a separate auto-save file, set the variable @code{auto-save-visited-file-name} to a non-@code{nil} value. In this mode, there is no real difference between auto-saving and explicit saving. @vindex delete-auto-save-files A buffer's auto-save file is deleted when you save the buffer in its visited file. (You can inhibit this by setting the variable @code{delete-auto-save-files} to @code{nil}.) Changing the visited file name with @kbd{C-x C-w} or @code{set-visited-file-name} renames any auto-save file to go with the new visited name. @node Auto Save Control @subsection Controlling Auto-Saving @vindex auto-save-default @findex auto-save-mode Each time you visit a file, auto-saving is turned on for that file's buffer if the variable @code{auto-save-default} is non-@code{nil} (but not in batch mode; @pxref{Entering Emacs}). The default for this variable is @code{t}, so auto-saving is the usual practice for file-visiting buffers. Auto-saving can be turned on or off for any existing buffer with the command @kbd{M-x auto-save-mode}. Like other minor mode commands, @kbd{M-x auto-save-mode} turns auto-saving on with a positive argument, off with a zero or negative argument; with no argument, it toggles. @vindex auto-save-interval Emacs does auto-saving periodically based on counting how many characters you have typed since the last time auto-saving was done. The variable @code{auto-save-interval} specifies how many characters there are between auto-saves. By default, it is 300. Emacs doesn't accept values that are too small: if you customize @code{auto-save-interval} to a value less than 20, Emacs will behave as if the value is 20. @vindex auto-save-timeout Auto-saving also takes place when you stop typing for a while. The variable @code{auto-save-timeout} says how many seconds Emacs should wait before it does an auto save (and perhaps also a garbage collection). (The actual time period is longer if the current buffer is long; this is a heuristic which aims to keep out of your way when you are editing long buffers, in which auto-save takes an appreciable amount of time.) Auto-saving during idle periods accomplishes two things: first, it makes sure all your work is saved if you go away from the terminal for a while; second, it may avoid some auto-saving while you are actually typing. Emacs also does auto-saving whenever it gets a fatal error. This includes killing the Emacs job with a shell command such as @samp{kill %emacs}, or disconnecting a phone line or network connection. @findex do-auto-save You can request an auto-save explicitly with the command @kbd{M-x do-auto-save}. @node Recover @subsection Recovering Data from Auto-Saves @findex recover-file You can use the contents of an auto-save file to recover from a loss of data with the command @kbd{M-x recover-file @key{RET} @var{file} @key{RET}}. This visits @var{file} and then (after your confirmation) restores the contents from its auto-save file @file{#@var{file}#}. You can then save with @kbd{C-x C-s} to put the recovered text into @var{file} itself. For example, to recover file @file{foo.c} from its auto-save file @file{#foo.c#}, do:@refill @example M-x recover-file @key{RET} foo.c @key{RET} yes @key{RET} C-x C-s @end example Before asking for confirmation, @kbd{M-x recover-file} displays a directory listing describing the specified file and the auto-save file, so you can compare their sizes and dates. If the auto-save file is older, @kbd{M-x recover-file} does not offer to read it. @findex recover-session If Emacs or the computer crashes, you can recover all the files you were editing from their auto save files with the command @kbd{M-x recover-session}. This first shows you a list of recorded interrupted sessions. Move point to the one you choose, and type @kbd{C-c C-c}. Then @code{recover-session} asks about each of the files that were being edited during that session, asking whether to recover that file. If you answer @kbd{y}, it calls @code{recover-file}, which works in its normal fashion. It shows the dates of the original file and its auto-save file, and asks once again whether to recover that file. When @code{recover-session} is done, the files you've chosen to recover are present in Emacs buffers. You should then save them. Only this---saving them---updates the files themselves. @vindex auto-save-list-file-prefix Emacs records information about interrupted sessions for later recovery in files named @file{~/.emacs.d/auto-save-list/.saves-@var{pid}-@var{hostname}}. All of this name except the @file{@var{pid}-@var{hostname}} part comes from the value of @code{auto-save-list-file-prefix}. You can record sessions in a different place by customizing that variable. If you set @code{auto-save-list-file-prefix} to @code{nil} in your @file{.emacs} file, sessions are not recorded for recovery. @node File Aliases @section File Name Aliases @cindex symbolic links (visiting) @cindex hard links (visiting) Symbolic links and hard links both make it possible for several file names to refer to the same file. Hard links are alternate names that refer directly to the file; all the names are equally valid, and no one of them is preferred. By contrast, a symbolic link is a kind of defined alias: when @file{foo} is a symbolic link to @file{bar}, you can use either name to refer to the file, but @file{bar} is the real name, while @file{foo} is just an alias. More complex cases occur when symbolic links point to directories. @vindex find-file-existing-other-name @vindex find-file-suppress-same-file-warnings Normally, if you visit a file which Emacs is already visiting under a different name, Emacs displays a message in the echo area and uses the existing buffer visiting that file. This can happen on systems that support hard or symbolic links, or if you use a long file name on a system that truncates long file names, or on a case-insensitive file system. You can suppress the message by setting the variable @code{find-file-suppress-same-file-warnings} to a non-@code{nil} value. You can disable this feature entirely by setting the variable @code{find-file-existing-other-name} to @code{nil}: then if you visit the same file under two different names, you get a separate buffer for each file name. @vindex find-file-visit-truename @cindex truenames of files @cindex file truenames If the variable @code{find-file-visit-truename} is non-@code{nil}, then the file name recorded for a buffer is the file's @dfn{truename} (made by replacing all symbolic links with their target names), rather than the name you specify. Setting @code{find-file-visit-truename} also implies the effect of @code{find-file-existing-other-name}. @node Version Control @section Version Control @cindex version control @dfn{Version control systems} are packages that can record multiple versions of a source file, usually storing the unchanged parts of the file just once. Version control systems also record history information such as the creation time of each version, who created it, and a description of what was changed in that version. The Emacs version control interface is called VC. Its commands work with different version control systems---currently, it supports CVS, GNU Arch, RCS, Meta-CVS, Subversion, and SCCS. Of these, the GNU project distributes CVS, GNU Arch, and RCS; we recommend that you use either CVS or GNU Arch for your projects, and RCS for individual files. We also have free software to replace SCCS, known as CSSC; if you are using SCCS and don't want to make the incompatible change to RCS or CVS, you can switch to CSSC. VC is enabled by default in Emacs. To disable it, set the customizable variable @code{vc-handled-backends} to @code{nil} @iftex (@pxref{Customizing VC,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{Customizing VC}). @end ifnottex @menu * Introduction to VC:: How version control works in general. * VC Mode Line:: How the mode line shows version control status. * Basic VC Editing:: How to edit a file under version control. * Old Versions:: Examining and comparing old versions. * Secondary VC Commands:: The commands used a little less frequently. * Branches:: Multiple lines of development. @ifnottex * Remote Repositories:: Efficient access to remote CVS servers. * Snapshots:: Sets of file versions treated as a unit. * Miscellaneous VC:: Various other commands and features of VC. * Customizing VC:: Variables that change VC's behavior. @end ifnottex @end menu @node Introduction to VC @subsection Introduction to Version Control VC allows you to use a version control system from within Emacs, integrating the version control operations smoothly with editing. VC provides a uniform interface to version control, so that regardless of which version control system is in use, you can use it the same way. This section provides a general overview of version control, and describes the version control systems that VC supports. You can skip this section if you are already familiar with the version control system you want to use. @menu * Version Systems:: Supported version control back-end systems. * VC Concepts:: Words and concepts related to version control. * Types of Log File:: The per-file VC log in contrast to the ChangeLog. @end menu @node Version Systems @subsubsection Supported Version Control Systems @cindex back end (version control) VC currently works with six different version control systems or ``back ends'': CVS, GNU Arch, RCS, Meta-CVS, Subversion, and SCCS. @cindex CVS CVS is a free version control system that is used for the majority of free software projects today. It allows concurrent multi-user development either locally or over the network. Some of its shortcomings, corrected by newer systems such as GNU Arch, are that it lacks atomic commits or support for renaming files. VC supports all basic editing operations under CVS, but for some less common tasks you still need to call CVS from the command line. Note also that before using CVS you must set up a repository, which is a subject too complex to treat here. @cindex GNU Arch @cindex Arch GNU Arch is a new version control system that is designed for distributed work. It differs in many ways from old well-known systems, such as CVS and RCS. It supports different transports for interoperating between users, offline operations, and it has good branching and merging features. It also supports atomic commits, and history of file renaming and moving. VC does not support all operations provided by GNU Arch, so you must sometimes invoke it from the command line, or use a specialized module. @cindex RCS RCS is the free version control system around which VC was initially built. The VC commands are therefore conceptually closest to RCS. Almost everything you can do with RCS can be done through VC. You cannot use RCS over the network though, and it only works at the level of individual files, rather than projects. You should use it if you want a simple, yet reliable tool for handling individual files. @cindex SVN @cindex Subversion Subversion is a free version control system designed to be similar to CVS but without CVS's problems. Subversion supports atomic commits, and versions directories, symbolic links, meta-data, renames, copies, and deletes. It can be used via http or via its own protocol. @cindex MCVS @cindex Meta-CVS Meta-CVS is another attempt to solve problems arising in CVS. It supports directory structure versioning, improved branching and merging, and use of symbolic links and meta-data in repositories. @cindex SCCS SCCS is a proprietary but widely used version control system. In terms of capabilities, it is the weakest of the six that VC supports. VC compensates for certain features missing in SCCS (snapshots, for example) by implementing them itself, but some other VC features, such as multiple branches, are not available with SCCS. Since SCCS is non-free, not respecting its users freedom, you should not use it; use its free replacement CSSC instead. But you should use CSSC only if for some reason you cannot use RCS, or one of the higher-level systems such as CVS or GNU Arch. In the following, we discuss mainly RCS, SCCS and CVS. Nearly everything said about CVS applies to GNU Arch, Subversion and Meta-CVS as well. @node VC Concepts @subsubsection Concepts of Version Control @cindex master file @cindex registered file When a file is under version control, we also say that it is @dfn{registered} in the version control system. Each registered file has a corresponding @dfn{master file} which represents the file's present state plus its change history---enough to reconstruct the current version or any earlier version. Usually the master file also records a @dfn{log entry} for each version, describing in words what was changed in that version. @cindex work file @cindex checking out files The file that is maintained under version control is sometimes called the @dfn{work file} corresponding to its master file. You edit the work file and make changes in it, as you would with an ordinary file. (With SCCS and RCS, you must @dfn{lock} the file before you start to edit it.) After you are done with a set of changes, you @dfn{check the file in}, which records the changes in the master file, along with a log entry for them. With CVS, there are usually multiple work files corresponding to a single master file---often each user has his own copy. It is also possible to use RCS in this way, but this is not the usual way to use RCS. @cindex locking and version control A version control system typically has some mechanism to coordinate between users who want to change the same file. One method is @dfn{locking} (analogous to the locking that Emacs uses to detect simultaneous editing of a file, but distinct from it). The other method is to merge your changes with other people's changes when you check them in. With version control locking, work files are normally read-only so that you cannot change them. You ask the version control system to make a work file writable for you by locking it; only one user can do this at any given time. When you check in your changes, that unlocks the file, making the work file read-only again. This allows other users to lock the file to make further changes. SCCS always uses locking, and RCS normally does. The other alternative for RCS is to let each user modify the work file at any time. In this mode, locking is not required, but it is permitted; check-in is still the way to record a new version. CVS normally allows each user to modify his own copy of the work file at any time, but requires merging with changes from other users at check-in time. However, CVS can also be set up to require locking. @iftex (@pxref{CVS Options,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{CVS Options}). @end ifnottex @node Types of Log File @subsubsection Types of Log File @cindex types of log file @cindex log File, types of @cindex version control log Projects that use a revision control system can have @emph{two} types of log for changes. One is the per-file log maintained by the revision control system: each time you check in a change, you must fill out a @dfn{log entry} for the change (@pxref{Log Buffer}). This kind of log is called the @dfn{version control log}, also the @dfn{revision control log}, @dfn{RCS log}, or @dfn{CVS log}. The other kind of log is the file @file{ChangeLog} (@pxref{Change Log}). It provides a chronological record of all changes to a large portion of a program---typically one directory and its subdirectories. A small program would use one @file{ChangeLog} file; a large program may well merit a @file{ChangeLog} file in each major directory. @xref{Change Log}. A project maintained with version control can use just the per-file log, or it can use both kinds of logs. It can handle some files one way and some files the other way. Each project has its policy, which you should follow. When the policy is to use both, you typically want to write an entry for each change just once, then put it into both logs. You can write the entry in @file{ChangeLog}, then copy it to the log buffer when you check in the change. Or you can write the entry in the log buffer while checking in the change, and later use the @kbd{C-x v a} command to copy it to @file{ChangeLog} @iftex (@pxref{Change Logs and VC,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{Change Logs and VC}). @end ifnottex @node VC Mode Line @subsection Version Control and the Mode Line When you visit a file that is under version control, Emacs indicates this on the mode line. For example, @samp{RCS-1.3} says that RCS is used for that file, and the current version is 1.3. The character between the back-end name and the version number indicates the version control status of the file. @samp{-} means that the work file is not locked (if locking is in use), or not modified (if locking is not in use). @samp{:} indicates that the file is locked, or that it is modified. If the file is locked by some other user (for instance, @samp{jim}), that is displayed as @samp{RCS:jim:1.3}. @vindex auto-revert-check-vc-info When Auto Revert mode (@pxref{Reverting}) reverts a buffer that is under version control, it updates the version control information in the mode line. However, Auto Revert mode may not properly update this information if the version control status changes without changes to the work file, from outside the current Emacs session. If you set @code{auto-revert-check-vc-info} to @code{t}, Auto Revert mode updates the version control status information every @code{auto-revert-interval} seconds, even if the work file itself is unchanged. The resulting CPU usage depends on the version control system, but is usually not excessive. @node Basic VC Editing @subsection Basic Editing under Version Control The principal VC command is an all-purpose command that performs either locking or check-in, depending on the situation. @table @kbd @itemx C-x v v Perform the next logical version control operation on this file. @end table @findex vc-next-action @kindex C-x v v The precise action of this command depends on the state of the file, and whether the version control system uses locking or not. SCCS and RCS normally use locking; CVS normally does not use locking. @findex vc-toggle-read-only @kindex C-x C-q @r{(Version Control)} As a special convenience that is particularly useful for files with locking, you can let Emacs check a file in or out whenever you change its read-only flag. This means, for example, that you cannot accidentally edit a file without properly checking it out first. To achieve this, bind the key @kbd{C-x C-q} to @kbd{vc-toggle-read-only} in your @file{~/.emacs} file. (@xref{Init Rebinding}.) @menu * VC with Locking:: RCS in its default mode, SCCS, and optionally CVS. * Without Locking:: Without locking: default mode for CVS. * Advanced C-x v v:: Advanced features available with a prefix argument. * Log Buffer:: Features available in log entry buffers. @end menu @node VC with Locking @subsubsection Basic Version Control with Locking If locking is used for the file (as with SCCS, and RCS in its default mode), @kbd{C-x v v} can either lock a file or check it in: @itemize @bullet @item If the file is not locked, @kbd{C-x v v} locks it, and makes it writable so that you can change it. @item If the file is locked by you, and contains changes, @kbd{C-x v v} checks in the changes. In order to do this, it first reads the log entry for the new version. @xref{Log Buffer}. @item If the file is locked by you, but you have not changed it since you locked it, @kbd{C-x v v} releases the lock and makes the file read-only again. @item If the file is locked by some other user, @kbd{C-x v v} asks you whether you want to ``steal the lock'' from that user. If you say yes, the file becomes locked by you, but a message is sent to the person who had formerly locked the file, to inform him of what has happened. @end itemize These rules also apply when you use CVS in locking mode, except that there is no such thing as stealing a lock. @node Without Locking @subsubsection Basic Version Control without Locking When there is no locking---the default for CVS---work files are always writable; you do not need to do anything before you begin to edit a file. The status indicator on the mode line is @samp{-} if the file is unmodified; it flips to @samp{:} as soon as you save any changes in the work file. Here is what @kbd{C-x v v} does when using CVS: @itemize @bullet @item If some other user has checked in changes into the master file, Emacs asks you whether you want to merge those changes into your own work file. You must do this before you can check in your own changes. (To pick up any recent changes from the master file @emph{without} trying to commit your own changes, type @kbd{C-x v m @key{RET}}.) @xref{Merging}. @item If there are no new changes in the master file, but you have made modifications in your work file, @kbd{C-x v v} checks in your changes. In order to do this, it first reads the log entry for the new version. @xref{Log Buffer}. @item If the file is not modified, the @kbd{C-x v v} does nothing. @end itemize These rules also apply when you use RCS in the mode that does not require locking, except that automatic merging of changes from the master file is not implemented. Unfortunately, this means that nothing informs you if another user has checked in changes in the same file since you began editing it, and when this happens, his changes will be effectively removed when you check in your version (though they will remain in the master file, so they will not be entirely lost). You must therefore verify that the current version is unchanged, before you check in your changes. We hope to eliminate this risk and provide automatic merging with RCS in a future Emacs version. In addition, locking is possible with RCS even in this mode, although it is not required; @kbd{C-x v v} with an unmodified file locks the file, just as it does with RCS in its normal (locking) mode. @node Advanced C-x v v @subsubsection Advanced Control in @kbd{C-x v v} @cindex version number to check in/out When you give a prefix argument to @code{vc-next-action} (@kbd{C-u C-x v v}), it still performs the next logical version control operation, but accepts additional arguments to specify precisely how to do the operation. @itemize @bullet @item If the file is modified (or locked), you can specify the version number to use for the new version that you check in. This is one way to create a new branch (@pxref{Branches}). @item If the file is not modified (and unlocked), you can specify the version to select; this lets you start working from an older version, or on another branch. If you do not enter any version, that takes you to the highest version on the current branch; therefore @kbd{C-u C-x v v @key{RET}} is a convenient way to get the latest version of a file from the repository. @item @cindex specific version control system Instead of the version number, you can also specify the name of a version control system. This is useful when one file is being managed with two version control systems at the same time @iftex (@pxref{Local Version Control,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{Local Version Control}). @end ifnottex @end itemize @node Log Buffer @subsubsection Features of the Log Entry Buffer When you check in changes, @kbd{C-x v v} first reads a log entry. It pops up a buffer called @samp{*VC-Log*} for you to enter the log entry. Sometimes the @samp{*VC-Log*} buffer contains default text when you enter it, typically the last log message entered. If it does, mark and point are set around the entire contents of the buffer so that it is easy to kill the contents of the buffer with @kbd{C-w}. @findex log-edit-insert-changelog If you work by writing entries in the @file{ChangeLog} (@pxref{Change Log}) and then commit the change under revision control, you can generate the Log Edit text from the ChangeLog using @kbd{C-c C-a} (@kbd{log-edit-insert-changelog}). This looks for entries for the file(s) concerned in the top entry in the ChangeLog and uses those paragraphs as the log text. This text is only inserted if the top entry was made under your user name on the current date. @iftex @xref{Change Logs and VC,,,emacs-xtra, Specialized Emacs Features}, @end iftex @ifnottex @xref{Change Logs and VC}, @end ifnottex for the opposite way of working---generating ChangeLog entries from the revision control log. In the @samp{*VC-Log*} buffer, @kbd{C-c C-f} (@kbd{M-x log-edit-show-files}) shows the list of files to be committed in case you need to check that. (This can be a list of more than one file if you use VC Dired mode or PCL-CVS. @iftex @xref{VC Dired Mode,,,emacs-xtra, Specialized Emacs Features}, @end iftex @ifnottex @xref{VC Dired Mode}, @end ifnottex and @ref{Top, , About PCL-CVS, pcl-cvs, PCL-CVS --- The Emacs Front-End to CVS}.) When you have finished editing the log message, type @kbd{C-c C-c} to exit the buffer and commit the change. To abort check-in, just @strong{don't} type @kbd{C-c C-c} in that buffer. You can switch buffers and do other editing. As long as you don't try to check in another file, the entry you were editing remains in the @samp{*VC-Log*} buffer, and you can go back to that buffer at any time to complete the check-in. If you change several source files for the same reason, it is often convenient to specify the same log entry for many of the files. To do this, use the history of previous log entries. The commands @kbd{M-n}, @kbd{M-p}, @kbd{M-s} and @kbd{M-r} for doing this work just like the minibuffer history commands (except that these versions are used outside the minibuffer). @vindex vc-log-mode-hook Each time you check in a file, the log entry buffer is put into VC Log mode, which involves running two hooks: @code{text-mode-hook} and @code{vc-log-mode-hook}. @xref{Hooks}. @node Old Versions @subsection Examining And Comparing Old Versions One of the convenient features of version control is the ability to examine any version of a file, or compare two versions. @table @kbd @item C-x v ~ @var{version} @key{RET} Examine version @var{version} of the visited file, in a buffer of its own. @item C-x v = Compare the current buffer contents with the master version from which you started editing. @item C-u C-x v = @var{file} @key{RET} @var{oldvers} @key{RET} @var{newvers} @key{RET} Compare the specified two versions of @var{file}. @item C-x v g Display the file with per-line version information and using colors. @end table @findex vc-version-other-window @kindex C-x v ~ To examine an old version in its entirety, visit the file and then type @kbd{C-x v ~ @var{version} @key{RET}} (@code{vc-version-other-window}). This puts the text of version @var{version} in a file named @file{@var{filename}.~@var{version}~}, and visits it in its own buffer in a separate window. (In RCS, you can also select an old version and create a branch from it. @xref{Branches}.) @findex vc-diff @kindex C-x v = It is usually more convenient to compare two versions of the file, with the command @kbd{C-x v =} (@code{vc-diff}). Plain @kbd{C-x v =} compares the current buffer contents (saving them in the file if necessary) with the master version from which you started editing the file (this is not necessarily the latest version of the file). @kbd{C-u C-x v =}, with a numeric argument, reads a file name and two version numbers, then compares those versions of the specified file. Both forms display the output in a special buffer in another window. You can specify a checked-in version by its number; an empty input specifies the current contents of the work file (which may be different from all the checked-in versions). You can also specify a snapshot name @iftex (@pxref{Snapshots,,,emacs-xtra, Specialized Emacs Features}) @end iftex @ifnottex (@pxref{Snapshots}) @end ifnottex instead of one or both version numbers. If you supply a directory name instead of the name of a registered file, this command compares the two specified versions of all registered files in that directory and its subdirectories. @vindex vc-diff-switches @vindex vc-rcs-diff-switches @kbd{C-x v =} works by running a variant of the @code{diff} utility designed to work with the version control system in use. When you invoke @code{diff} this way, in addition to the options specified by @code{diff-switches} (@pxref{Comparing Files}), it receives those specified by @code{vc-diff-switches}, plus those specified for the specific back end by @code{vc-@var{backend}-diff-switches}. For instance, when the version control back end is RCS, @code{diff} uses the options in @code{vc-rcs-diff-switches}. The @samp{vc@dots{}diff-switches} variables are @code{nil} by default. The buffer produced by @kbd{C-x v =} supports the commands of Compilation mode (@pxref{Compilation Mode}), such as @kbd{C-x `} and @kbd{C-c C-c}, in both the ``old'' and ``new'' text, and they always find the corresponding locations in the current work file. (Older versions are not, in general, present as files on your disk.) @findex vc-annotate @kindex C-x v g For some back ends, you can display the file @dfn{annotated} with per-line version information and using colors to enhance the visual appearance, with the command @kbd{M-x vc-annotate}. It creates a new buffer (the ``annotate buffer'') displaying the file's text, with each part colored to show how old it is. Text colored red is new, blue means old, and intermediate colors indicate intermediate ages. By default, the color is scaled over the full range of ages, such that the oldest changes are blue, and the newest changes are red. When you give a prefix argument to this command, it uses the minibuffer to read two arguments: which version number to display and annotate (instead of the current file contents), and the time span in days the color range should cover. From the annotate buffer, these and other color scaling options are available from the @samp{VC-Annotate} menu. In this buffer, you can also use the following keys to browse the annotations of past revisions, view diffs, or view log entries: @table @kbd @item P Annotate the previous revision, that is to say, the revision before the one currently annotated. A numeric prefix argument is a repeat count, so @kbd{C-u 10 P} would take you back 10 revisions. @item N Annotate the next revision---the one after the revision currently annotated. A numeric prefix argument is a repeat count. @item J Annotate the revision indicated by the current line. @item A Annotate the revision before the one indicated by the current line. This is useful to see the state the file was in before the change on the current line was made. @item D Display the diff between the current line's revision and the previous revision. This is useful to see what the current line's revision actually changed in the file. @item L Show the log of the current line's revision. This is useful to see the author's description of the changes in the revision on the current line. @item W Annotate the workfile version--the one you are editing. If you used @kbd{P} and @kbd{N} to browse to other revisions, use this key to return to your current version. @end table @node Secondary VC Commands @subsection The Secondary Commands of VC This section explains the secondary commands of VC; those that you might use once a day. @menu * Registering:: Putting a file under version control. * VC Status:: Viewing the VC status of files. * VC Undo:: Canceling changes before or after check-in. @ifnottex * VC Dired Mode:: Listing files managed by version control. * VC Dired Commands:: Commands to use in a VC Dired buffer. @end ifnottex @end menu @node Registering @subsubsection Registering a File for Version Control @kindex C-x v i @findex vc-register You can put any file under version control by simply visiting it, and then typing @w{@kbd{C-x v i}} (@code{vc-register}). @table @kbd @item C-x v i Register the visited file for version control. @end table To register the file, Emacs must choose which version control system to use for it. If the file's directory already contains files registered in a version control system, Emacs uses that system. If there is more than one system in use for a directory, Emacs uses the one that appears first in @code{vc-handled-backends} @iftex (@pxref{Customizing VC,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{Customizing VC}). @end ifnottex On the other hand, if there are no files already registered, Emacs uses the first system from @code{vc-handled-backends} that could register the file (for example, you cannot register a file under CVS if its directory is not already part of a CVS tree); with the default value of @code{vc-handled-backends}, this means that Emacs uses RCS in this situation. If locking is in use, @kbd{C-x v i} leaves the file unlocked and read-only. Type @kbd{C-x v v} if you wish to start editing it. After registering a file with CVS, you must subsequently commit the initial version by typing @kbd{C-x v v}. Until you do that, the version appears as @samp{@@@@} in the mode line. @vindex vc-default-init-version @cindex initial version number to register The initial version number for a newly registered file is 1.1, by default. You can specify a different default by setting the variable @code{vc-default-init-version}, or you can give @kbd{C-x v i} a numeric argument; then it reads the initial version number for this particular file using the minibuffer. @vindex vc-initial-comment If @code{vc-initial-comment} is non-@code{nil}, @kbd{C-x v i} reads an initial comment to describe the purpose of this source file. Reading the initial comment works like reading a log entry (@pxref{Log Buffer}). @node VC Status @subsubsection VC Status Commands @table @kbd @item C-x v l Display version control state and change history. @end table @kindex C-x v l @findex vc-print-log To view the detailed version control status and history of a file, type @kbd{C-x v l} (@code{vc-print-log}). It displays the history of changes to the current file, including the text of the log entries. The output appears in a separate window. The point is centered at the revision of the file that is currently being visited. In the change log buffer, you can use the following keys to move between the logs of revisions and of files, to view past revisions, and to view diffs: @table @kbd @item p Move to the previous revision-item in the buffer. (Revision entries in the log buffer are usually in reverse-chronological order, so the previous revision-item usually corresponds to a newer revision.) A numeric prefix argument is a repeat count. @item n Move to the next revision-item (which most often corresponds to the previous revision of the file). A numeric prefix argument is a repeat count. @item P Move to the log of the previous file, when the logs of multiple files are in the log buffer @iftex (@pxref{VC Dired Mode,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{VC Dired Mode}). @end ifnottex Otherwise, just move to the beginning of the log. A numeric prefix argument is a repeat count, so @kbd{C-u 10 P} would move backward 10 files. @item N Move to the log of the next file, when the logs of multiple files are in the log buffer @iftex (@pxref{VC Dired Mode,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{VC Dired Mode}). @end ifnottex It also takes a numeric prefix argument as a repeat count. @item f Visit the revision indicated at the current line, like typing @kbd{C-x v ~} and specifying this revision's number (@pxref{Old Versions}). @item d Display the diff (@pxref{Comparing Files}) between the revision indicated at the current line and the next earlier revision. This is useful to see what actually changed when the revision indicated on the current line was committed. @end table @node VC Undo @subsubsection Undoing Version Control Actions @table @kbd @item C-x v u Revert the buffer and the file to the version from which you started editing the file. @item C-x v c Remove the last-entered change from the master for the visited file. This undoes your last check-in. @end table @kindex C-x v u @findex vc-revert-buffer If you want to discard your current set of changes and revert to the version from which you started editing the file, use @kbd{C-x v u} (@code{vc-revert-buffer}). This leaves the file unlocked; if locking is in use, you must first lock the file again before you change it again. @kbd{C-x v u} requires confirmation, unless it sees that you haven't made any changes with respect to the master version. @kbd{C-x v u} is also the command to unlock a file if you lock it and then decide not to change it. @kindex C-x v c @findex vc-cancel-version To cancel a change that you already checked in, use @kbd{C-x v c} (@code{vc-cancel-version}). This command discards all record of the most recent checked-in version, but only if your work file corresponds to that version---you cannot use @kbd{C-x v c} to cancel a version that is not the latest on its branch. @kbd{C-x v c} also offers to revert your work file and buffer to the previous version (the one that precedes the version that is deleted). If you answer @kbd{no}, VC keeps your changes in the buffer, and locks the file. The no-revert option is useful when you have checked in a change and then discover a trivial error in it; you can cancel the erroneous check-in, fix the error, and check the file in again. When @kbd{C-x v c} does not revert the buffer, it unexpands all version control headers in the buffer instead @iftex (@pxref{Version Headers,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{Version Headers}). @end ifnottex This is because the buffer no longer corresponds to any existing version. If you check it in again, the check-in process will expand the headers properly for the new version number. However, it is impossible to unexpand the RCS @samp{@w{$}Log$} header automatically. If you use that header feature, you have to unexpand it by hand---by deleting the entry for the version that you just canceled. Be careful when invoking @kbd{C-x v c}, as it is easy to lose a lot of work with it. To help you be careful, this command always requires confirmation with @kbd{yes}. Note also that this command is disabled under CVS, because canceling versions is very dangerous and discouraged with CVS. @ifnottex @c vc1-xtra.texi needs extra level of lowering. @lowersections @include vc1-xtra.texi @raisesections @end ifnottex @node Branches @subsection Multiple Branches of a File @cindex branch (version control) @cindex trunk (version control) One use of version control is to maintain multiple ``current'' versions of a file. For example, you might have different versions of a program in which you are gradually adding various unfinished new features. Each such independent line of development is called a @dfn{branch}. VC allows you to create branches, switch between different branches, and merge changes from one branch to another. Please note, however, that branches are not supported for SCCS. A file's main line of development is usually called the @dfn{trunk}. The versions on the trunk are normally numbered 1.1, 1.2, 1.3, etc. At any such version, you can start an independent branch. A branch starting at version 1.2 would have version number 1.2.1.1, and consecutive versions on this branch would have numbers 1.2.1.2, 1.2.1.3, 1.2.1.4, and so on. If there is a second branch also starting at version 1.2, it would consist of versions 1.2.2.1, 1.2.2.2, 1.2.2.3, etc. @cindex head version If you omit the final component of a version number, that is called a @dfn{branch number}. It refers to the highest existing version on that branch---the @dfn{head version} of that branch. The branches in the example above have branch numbers 1.2.1 and 1.2.2. @menu * Switching Branches:: How to get to another existing branch. * Creating Branches:: How to start a new branch. * Merging:: Transferring changes between branches. * Multi-User Branching:: Multiple users working at multiple branches in parallel. @end menu @node Switching Branches @subsubsection Switching between Branches To switch between branches, type @kbd{C-u C-x v v} and specify the version number you want to select. This version is then visited @emph{unlocked} (write-protected), so you can examine it before locking it. Switching branches in this way is allowed only when the file is not locked. You can omit the minor version number, thus giving only the branch number; this takes you to the head version on the chosen branch. If you only type @key{RET}, Emacs goes to the highest version on the trunk. After you have switched to any branch (including the main branch), you stay on it for subsequent VC commands, until you explicitly select some other branch. @node Creating Branches @subsubsection Creating New Branches To create a new branch from a head version (one that is the latest in the branch that contains it), first select that version if necessary, lock it with @kbd{C-x v v}, and make whatever changes you want. Then, when you check in the changes, use @kbd{C-u C-x v v}. This lets you specify the version number for the new version. You should specify a suitable branch number for a branch starting at the current version. For example, if the current version is 2.5, the branch number should be 2.5.1, 2.5.2, and so on, depending on the number of existing branches at that point. To create a new branch at an older version (one that is no longer the head of a branch), first select that version (@pxref{Switching Branches}), then lock it with @kbd{C-x v v}. You'll be asked to confirm, when you lock the old version, that you really mean to create a new branch---if you say no, you'll be offered a chance to lock the latest version instead. Then make your changes and type @kbd{C-x v v} again to check in a new version. This automatically creates a new branch starting from the selected version. You need not specially request a new branch, because that's the only way to add a new version at a point that is not the head of a branch. After the branch is created, you ``stay'' on it. That means that subsequent check-ins create new versions on that branch. To leave the branch, you must explicitly select a different version with @kbd{C-u C-x v v}. To transfer changes from one branch to another, use the merge command, described in the next section. @node Merging @subsubsection Merging Branches @cindex merging changes When you have finished the changes on a certain branch, you will often want to incorporate them into the file's main line of development (the trunk). This is not a trivial operation, because development might also have proceeded on the trunk, so that you must @dfn{merge} the changes into a file that has already been changed otherwise. VC allows you to do this (and other things) with the @code{vc-merge} command. @table @kbd @item C-x v m (vc-merge) Merge changes into the work file. @end table @kindex C-x v m @findex vc-merge @kbd{C-x v m} (@code{vc-merge}) takes a set of changes and merges it into the current version of the work file. It firsts asks you in the minibuffer where the changes should come from. If you just type @key{RET}, Emacs merges any changes that were made on the same branch since you checked the file out (we call this @dfn{merging the news}). This is the common way to pick up recent changes from the repository, regardless of whether you have already changed the file yourself. You can also enter a branch number or a pair of version numbers in the minibuffer. Then @kbd{C-x v m} finds the changes from that branch, or the differences between the two versions you specified, and merges them into the current version of the current file. As an example, suppose that you have finished a certain feature on branch 1.3.1. In the meantime, development on the trunk has proceeded to version 1.5. To merge the changes from the branch to the trunk, first go to the head version of the trunk, by typing @kbd{C-u C-x v v @key{RET}}. Version 1.5 is now current. If locking is used for the file, type @kbd{C-x v v} to lock version 1.5 so that you can change it. Next, type @kbd{C-x v m 1.3.1 @key{RET}}. This takes the entire set of changes on branch 1.3.1 (relative to version 1.3, where the branch started, up to the last version on the branch) and merges it into the current version of the work file. You can now check in the changed file, thus creating version 1.6 containing the changes from the branch. It is possible to do further editing after merging the branch, before the next check-in. But it is usually wiser to check in the merged version, then lock it and make the further changes. This will keep a better record of the history of changes. @cindex conflicts @cindex resolving conflicts When you merge changes into a file that has itself been modified, the changes might overlap. We call this situation a @dfn{conflict}, and reconciling the conflicting changes is called @dfn{resolving a conflict}. Whenever conflicts occur during merging, VC detects them, tells you about them in the echo area, and asks whether you want help in merging. If you say yes, it starts an Ediff session (@pxref{Top, Ediff, Ediff, ediff, The Ediff Manual}). If you say no, the conflicting changes are both inserted into the file, surrounded by @dfn{conflict markers}. The example below shows how a conflict region looks; the file is called @samp{name} and the current master file version with user B's changes in it is 1.11. @c @w here is so CVS won't think this is a conflict. @smallexample @group @w{<}<<<<<< name @var{User A's version} ======= @var{User B's version} @w{>}>>>>>> 1.11 @end group @end smallexample @cindex vc-resolve-conflicts Then you can resolve the conflicts by editing the file manually. Or you can type @code{M-x vc-resolve-conflicts} after visiting the file. This starts an Ediff session, as described above. Don't forget to check in the merged version afterwards. @node Multi-User Branching @subsubsection Multi-User Branching It is often useful for multiple developers to work simultaneously on different branches of a file. CVS allows this by default; for RCS, it is possible if you create multiple source directories. Each source directory should have a link named @file{RCS} which points to a common directory of RCS master files. Then each source directory can have its own choice of selected versions, but all share the same common RCS records. This technique works reliably and automatically, provided that the source files contain RCS version headers @iftex (@pxref{Version Headers,,,emacs-xtra, Specialized Emacs Features}). @end iftex @ifnottex (@pxref{Version Headers}). @end ifnottex The headers enable Emacs to be sure, at all times, which version number is present in the work file. If the files do not have version headers, you must instead tell Emacs explicitly in each session which branch you are working on. To do this, first find the file, then type @kbd{C-u C-x v v} and specify the correct branch number. This ensures that Emacs knows which branch it is using during this particular editing session. @ifnottex @include vc2-xtra.texi @end ifnottex @node Directories @section File Directories @cindex file directory @cindex directory listing The file system groups files into @dfn{directories}. A @dfn{directory listing} is a list of all the files in a directory. Emacs provides commands to create and delete directories, and to make directory listings in brief format (file names only) and verbose format (sizes, dates, and authors included). Emacs also includes a directory browser feature called Dired; see @ref{Dired}. @table @kbd @item C-x C-d @var{dir-or-pattern} @key{RET} Display a brief directory listing (@code{list-directory}). @item C-u C-x C-d @var{dir-or-pattern} @key{RET} Display a verbose directory listing. @item M-x make-directory @key{RET} @var{dirname} @key{RET} Create a new directory named @var{dirname}. @item M-x delete-directory @key{RET} @var{dirname} @key{RET} Delete the directory named @var{dirname}. It must be empty, or you get an error. @end table @findex list-directory @kindex C-x C-d The command to display a directory listing is @kbd{C-x C-d} (@code{list-directory}). It reads using the minibuffer a file name which is either a directory to be listed or a wildcard-containing pattern for the files to be listed. For example, @example C-x C-d /u2/emacs/etc @key{RET} @end example @noindent lists all the files in directory @file{/u2/emacs/etc}. Here is an example of specifying a file name pattern: @example C-x C-d /u2/emacs/src/*.c @key{RET} @end example Normally, @kbd{C-x C-d} displays a brief directory listing containing just file names. A numeric argument (regardless of value) tells it to make a verbose listing including sizes, dates, and owners (like @samp{ls -l}). @vindex list-directory-brief-switches @vindex list-directory-verbose-switches The text of a directory listing is mostly obtained by running @code{ls} in an inferior process. Two Emacs variables control the switches passed to @code{ls}: @code{list-directory-brief-switches} is a string giving the switches to use in brief listings (@code{"-CF"} by default), and @code{list-directory-verbose-switches} is a string giving the switches to use in a verbose listing (@code{"-l"} by default). @vindex directory-free-space-program @vindex directory-free-space-args In verbose directory listings, Emacs adds information about the amount of free space on the disk that contains the directory. To do this, it runs the program specified by @code{directory-free-space-program} with arguments @code{directory-free-space-args}. @node Comparing Files @section Comparing Files @cindex comparing files @findex diff @vindex diff-switches The command @kbd{M-x diff} compares two files, displaying the differences in an Emacs buffer named @samp{*diff*}. It works by running the @code{diff} program, using options taken from the variable @code{diff-switches}. The value of @code{diff-switches} should be a string; the default is @code{"-c"} to specify a context diff. @xref{Top,, Diff, diff, Comparing and Merging Files}, for more information about @command{diff} output formats. @findex diff-backup The command @kbd{M-x diff-backup} compares a specified file with its most recent backup. If you specify the name of a backup file, @code{diff-backup} compares it with the source file that it is a backup of. @findex compare-windows The command @kbd{M-x compare-windows} compares the text in the current window with that in the next window. (For more information about windows in Emacs, @ref{Windows}.) Comparison starts at point in each window, after pushing each initial point value on the mark ring in its respective buffer. Then it moves point forward in each window, one character at a time, until it reaches characters that don't match. Then the command exits. If point in the two windows is followed by non-matching text when the command starts, @kbd{M-x compare-windows} tries heuristically to advance up to matching text in the two windows, and then exits. So if you use @kbd{M-x compare-windows} repeatedly, each time it either skips one matching range or finds the start of another. @vindex compare-ignore-case @vindex compare-ignore-whitespace With a numeric argument, @code{compare-windows} ignores changes in whitespace. If the variable @code{compare-ignore-case} is non-@code{nil}, the comparison ignores differences in case as well. If the variable @code{compare-ignore-whitespace} is non-@code{nil}, @code{compare-windows} normally ignores changes in whitespace, and a prefix argument turns that off. @cindex Smerge mode @findex smerge-mode @cindex failed merges @cindex merges, failed @cindex comparing 3 files (@code{diff3}) You can use @kbd{M-x smerge-mode} to turn on Smerge mode, a minor mode for editing output from the @command{diff3} program. This is typically the result of a failed merge from a version control system ``update'' outside VC, due to conflicting changes to a file. Smerge mode provides commands to resolve conflicts by selecting specific changes. @iftex @xref{Emerge,,, emacs-xtra, Specialized Emacs Features}, @end iftex @ifnottex @xref{Emerge}, @end ifnottex for the Emerge facility, which provides a powerful interface for merging files. @node Diff Mode @section Diff Mode @cindex Diff mode @findex diff-mode @cindex patches, editing Diff mode is used for the output of @kbd{M-x diff}; it is also useful for editing patches and comparisons produced by the @command{diff} program. To select Diff mode manually, type @kbd{M-x diff-mode}. One general feature of Diff mode is that manual edits to the patch automatically correct line numbers, including those in the hunk header, so that you can actually apply the edited patch. Diff mode treats each hunk location as an ``error message,'' so that you can use commands such as @kbd{C-x '} to visit the corresponding source locations. It also provides the following commands to navigate, manipulate and apply parts of patches: @table @kbd @item M-n Move to the next hunk-start (@code{diff-hunk-next}). @item M-p Move to the previous hunk-start (@code{diff-hunk-prev}). @item M-@} Move to the next file-start, in a multi-file patch (@code{diff-file-next}). @item M-@{ Move to the previous file-start, in a multi-file patch (@code{diff-file-prev}). @item M-k Kill the hunk at point (@code{diff-hunk-kill}). @item M-K In a multi-file patch, kill the current file part. (@code{diff-file-kill}). @item C-c C-a Apply this hunk to its target file (@code{diff-apply-hunk}). With a prefix argument of @kbd{C-u}, revert this hunk. @item C-c C-c Go to the source corresponding to this hunk (@code{diff-goto-source}). @item C-c C-e Start an Ediff session with the patch (@code{diff-ediff-patch}). @xref{Top, Ediff, Ediff, ediff, The Ediff Manual}. @item C-c C-n Restrict the view to the current hunk (@code{diff-restrict-view}). @xref{Narrowing}. With a prefix argument of @kbd{C-u}, restrict the view to the current patch of a multiple file patch. To widen again, use @kbd{C-x n w}. @item C-c C-r Reverse the direction of comparison for the entire buffer (@code{diff-reverse-direction}). @item C-c C-s Split the hunk at point (@code{diff-split-hunk}). This is for manually editing patches, and only works with the unified diff format. @item C-c C-u Convert the entire buffer to unified format (@code{diff-context->unified}). With a prefix argument, convert unified format to context format. In Transient Mark mode, when the mark is active, this command operates only on the region. @item C-c C-w Refine the current hunk so that it disregards changes in whitespace (@code{diff-refine-hunk}). @end table @kbd{C-x 4 a} in Diff mode operates on behalf of the target file, but gets the function name from the patch itself. @xref{Change Log}. This is useful for making log entries for functions that are deleted by the patch. @node Misc File Ops @section Miscellaneous File Operations Emacs has commands for performing many other operations on files. All operate on one file; they do not accept wildcard file names. @findex view-file @cindex viewing @cindex View mode @cindex mode, View @kbd{M-x view-file} allows you to scan or read a file by sequential screenfuls. It reads a file name argument using the minibuffer. After reading the file into an Emacs buffer, @code{view-file} displays the beginning. You can then type @key{SPC} to scroll forward one windowful, or @key{DEL} to scroll backward. Various other commands are provided for moving around in the file, but none for changing it; type @kbd{?} while viewing for a list of them. They are mostly the same as normal Emacs cursor motion commands. To exit from viewing, type @kbd{q}. The commands for viewing are defined by a special minor mode called View mode. A related command, @kbd{M-x view-buffer}, views a buffer already present in Emacs. @xref{Misc Buffer}. @kindex C-x i @findex insert-file @kbd{M-x insert-file} (also @kbd{C-x i}) inserts a copy of the contents of the specified file into the current buffer at point, leaving point unchanged before the contents and the mark after them. @findex insert-file-literally @kbd{M-x insert-file-literally} is like @kbd{M-x insert-file}, except the file is inserted ``literally'': it is treated as a sequence of @acronym{ASCII} characters with no special encoding or conversion, similar to the @kbd{M-x find-file-literally} command (@pxref{Visiting}). @findex write-region @kbd{M-x write-region} is the inverse of @kbd{M-x insert-file}; it copies the contents of the region into the specified file. @kbd{M-x append-to-file} adds the text of the region to the end of the specified file. @xref{Accumulating Text}. The variable @code{write-region-inhibit-fsync} applies to these commands, as well as saving files; see @ref{Customize Save}. @findex delete-file @cindex deletion (of files) @kbd{M-x delete-file} deletes the specified file, like the @code{rm} command in the shell. If you are deleting many files in one directory, it may be more convenient to use Dired (@pxref{Dired}). @findex rename-file @kbd{M-x rename-file} reads two file names @var{old} and @var{new} using the minibuffer, then renames file @var{old} as @var{new}. If the file name @var{new} already exists, you must confirm with @kbd{yes} or renaming is not done; this is because renaming causes the old meaning of the name @var{new} to be lost. If @var{old} and @var{new} are on different file systems, the file @var{old} is copied and deleted. If the argument @var{new} is just a directory name, the real new name is in that directory, with the same non-directory component as @var{old}. For example, @kbd{M-x rename-file RET ~/foo RET /tmp RET} renames @file{~/foo} to @file{/tmp/foo}. The same rule applies to all the remaining commands in this section. All of them ask for confirmation when the new file name already exists, too. @findex add-name-to-file @cindex hard links (creation) The similar command @kbd{M-x add-name-to-file} is used to add an additional name to an existing file without removing its old name. The new name is created as a ``hard link'' to the existing file. The new name must belong on the same file system that the file is on. On MS-Windows, this command works only if the file resides in an NTFS file system. On MS-DOS, it works by copying the file. @findex copy-file @cindex copying files @kbd{M-x copy-file} reads the file @var{old} and writes a new file named @var{new} with the same contents. @findex make-symbolic-link @cindex symbolic links (creation) @kbd{M-x make-symbolic-link} reads two file names @var{target} and @var{linkname}, then creates a symbolic link named @var{linkname}, which points at @var{target}. The effect is that future attempts to open file @var{linkname} will refer to whatever file is named @var{target} at the time the opening is done, or will get an error if the name @var{target} is nonexistent at that time. This command does not expand the argument @var{target}, so that it allows you to specify a relative name as the target of the link. Not all systems support symbolic links; on systems that don't support them, this command is not defined. @node Compressed Files @section Accessing Compressed Files @cindex compression @cindex uncompression @cindex Auto Compression mode @cindex mode, Auto Compression @pindex gzip Emacs automatically uncompresses compressed files when you visit them, and automatically recompresses them if you alter them and save them. Emacs recognizes compressed files by their file names. File names ending in @samp{.gz} indicate a file compressed with @code{gzip}. Other endings indicate other compression programs. Automatic uncompression and compression apply to all the operations in which Emacs uses the contents of a file. This includes visiting it, saving it, inserting its contents into a buffer, loading it, and byte compiling it. @findex auto-compression-mode @vindex auto-compression-mode To disable this feature, type the command @kbd{M-x auto-compression-mode}. You can disable it permanently by customizing the variable @code{auto-compression-mode}. @node File Archives @section File Archives @cindex mode, tar @cindex Tar mode @cindex file archives A file whose name ends in @samp{.tar} is normally an @dfn{archive} made by the @code{tar} program. Emacs views these files in a special mode called Tar mode which provides a Dired-like list of the contents (@pxref{Dired}). You can move around through the list just as you would in Dired, and visit the subfiles contained in the archive. However, not all Dired commands are available in Tar mode. If Auto Compression mode is enabled (@pxref{Compressed Files}), then Tar mode is used also for compressed archives---files with extensions @samp{.tgz}, @code{.tar.Z} and @code{.tar.gz}. The keys @kbd{e}, @kbd{f} and @key{RET} all extract a component file into its own buffer. You can edit it there, and if you save the buffer, the edited version will replace the version in the Tar buffer. @kbd{v} extracts a file into a buffer in View mode. @kbd{o} extracts the file and displays it in another window, so you could edit the file and operate on the archive simultaneously. @kbd{d} marks a file for deletion when you later use @kbd{x}, and @kbd{u} unmarks a file, as in Dired. @kbd{C} copies a file from the archive to disk and @kbd{R} renames a file within the archive. @kbd{g} reverts the buffer from the archive on disk. The keys @kbd{M}, @kbd{G}, and @kbd{O} change the file's permission bits, group, and owner, respectively. If your display supports colors and the mouse, moving the mouse pointer across a file name highlights that file name, indicating that you can click on it. Clicking @kbd{Mouse-2} on the highlighted file name extracts the file into a buffer and displays that buffer. Saving the Tar buffer writes a new version of the archive to disk with the changes you made to the components. You don't need the @code{tar} program to use Tar mode---Emacs reads the archives directly. However, accessing compressed archives requires the appropriate uncompression program. @cindex Archive mode @cindex mode, archive @cindex @code{arc} @cindex @code{jar} @cindex @code{zip} @cindex @code{lzh} @cindex @code{zoo} @pindex arc @pindex jar @pindex zip @pindex lzh @pindex zoo @cindex Java class archives @cindex unzip archives A separate but similar Archive mode is used for archives produced by the programs @code{arc}, @code{jar}, @code{lzh}, @code{zip}, and @code{zoo}, which have extensions corresponding to the program names. Archive mode also works for those @code{exe} files that are self-extracting executables. The key bindings of Archive mode are similar to those in Tar mode, with the addition of the @kbd{m} key which marks a file for subsequent operations, and @kbd{M-@key{DEL}} which unmarks all the marked files. Also, the @kbd{a} key toggles the display of detailed file information, for those archive types where it won't fit in a single line. Operations such as renaming a subfile, or changing its mode or owner, are supported only for some of the archive formats. Unlike Tar mode, Archive mode runs the archiving program to unpack and repack archives. Details of the program names and their options can be set in the @samp{Archive} Customize group. However, you don't need these programs to look at the archive table of contents, only to extract or manipulate the subfiles in the archive. @node Remote Files @section Remote Files @cindex Tramp @cindex FTP @cindex remote file access You can refer to files on other machines using a special file name syntax: @example @group /@var{host}:@var{filename} /@var{user}@@@var{host}:@var{filename} /@var{user}@@@var{host}#@var{port}:@var{filename} /@var{method}:@var{user}@@@var{host}:@var{filename} /@var{method}:@var{user}@@@var{host}#@var{port}:@var{filename} @end group @end example @noindent To carry out this request, Emacs uses either the FTP program or a remote-login program such as @command{ssh}, @command{rlogin}, or @command{telnet}. You can always specify in the file name which method to use---for example, @file{/ftp:@var{user}@@@var{host}:@var{filename}} uses FTP, whereas @file{/ssh:@var{user}@@@var{host}:@var{filename}} uses @command{ssh}. When you don't specify a method in the file name, Emacs chooses the method as follows: @enumerate @item If the host name starts with @samp{ftp.} (with dot), then Emacs uses FTP. @item If the user name is @samp{ftp} or @samp{anonymous}, then Emacs uses FTP. @item Otherwise, Emacs uses @command{ssh}. @end enumerate @noindent Remote file access through FTP is handled by the Ange-FTP package, which is documented in the following. Remote file access through the other methods is handled by the Tramp package, which has its own manual. @xref{Top, The Tramp Manual,, tramp, The Tramp Manual}. When the Ange-FTP package is used, Emacs logs in through FTP using your user name or the name @var{user}. It may ask you for a password from time to time; this is used for logging in on @var{host}. The form using @var{port} allows you to access servers running on a non-default TCP port. @cindex backups for remote files @vindex ange-ftp-make-backup-files If you want to disable backups for remote files, set the variable @code{ange-ftp-make-backup-files} to @code{nil}. By default, the auto-save files (@pxref{Auto Save Files}) for remote files are made in the temporary file directory on the local machine. This is achieved using the variable @code{auto-save-file-name-transforms}. @cindex ange-ftp @vindex ange-ftp-default-user @cindex user name for remote file access Normally, if you do not specify a user name in a remote file name, that means to use your own user name. But if you set the variable @code{ange-ftp-default-user} to a string, that string is used instead. @cindex anonymous FTP @vindex ange-ftp-generate-anonymous-password To visit files accessible by anonymous FTP, you use special user names @samp{anonymous} or @samp{ftp}. Passwords for these user names are handled specially. The variable @code{ange-ftp-generate-anonymous-password} controls what happens: if the value of this variable is a string, then that string is used as the password; if non-@code{nil} (the default), then the value of @code{user-mail-address} is used; if @code{nil}, then Emacs prompts you for a password as usual. @cindex firewall, and accessing remote files @cindex gateway, and remote file access with @code{ange-ftp} @vindex ange-ftp-smart-gateway @vindex ange-ftp-gateway-host Sometimes you may be unable to access files on a remote machine because a @dfn{firewall} in between blocks the connection for security reasons. If you can log in on a @dfn{gateway} machine from which the target files @emph{are} accessible, and whose FTP server supports gatewaying features, you can still use remote file names; all you have to do is specify the name of the gateway machine by setting the variable @code{ange-ftp-gateway-host}, and set @code{ange-ftp-smart-gateway} to @code{t}. Otherwise you may be able to make remote file names work, but the procedure is complex. You can read the instructions by typing @kbd{M-x finder-commentary @key{RET} ange-ftp @key{RET}}. @vindex file-name-handler-alist @cindex disabling remote files You can entirely turn off the FTP file name feature by removing the entries @code{ange-ftp-completion-hook-function} and @code{ange-ftp-hook-function} from the variable @code{file-name-handler-alist}. You can turn off the feature in individual cases by quoting the file name with @samp{/:} (@pxref{Quoted File Names}). @node Quoted File Names @section Quoted File Names @cindex quoting file names @cindex file names, quote special characters You can @dfn{quote} an absolute file name to prevent special characters and syntax in it from having their special effects. The way to do this is to add @samp{/:} at the beginning. For example, you can quote a local file name which appears remote, to prevent it from being treated as a remote file name. Thus, if you have a directory named @file{/foo:} and a file named @file{bar} in it, you can refer to that file in Emacs as @samp{/:/foo:/bar}. @samp{/:} can also prevent @samp{~} from being treated as a special character for a user's home directory. For example, @file{/:/tmp/~hack} refers to a file whose name is @file{~hack} in directory @file{/tmp}. Quoting with @samp{/:} is also a way to enter in the minibuffer a file name that contains @samp{$}. In order for this to work, the @samp{/:} must be at the beginning of the minibuffer contents. (You can also double each @samp{$}; see @ref{File Names with $}.) You can also quote wildcard characters with @samp{/:}, for visiting. For example, @file{/:/tmp/foo*bar} visits the file @file{/tmp/foo*bar}. Another method of getting the same result is to enter @file{/tmp/foo[*]bar}, which is a wildcard specification that matches only @file{/tmp/foo*bar}. However, in many cases there is no need to quote the wildcard characters because even unquoted they give the right result. For example, if the only file name in @file{/tmp} that starts with @samp{foo} and ends with @samp{bar} is @file{foo*bar}, then specifying @file{/tmp/foo*bar} will visit only @file{/tmp/foo*bar}. @node File Name Cache @section File Name Cache @cindex file name caching @cindex cache of file names @pindex find @kindex C-@key{TAB} @findex file-cache-minibuffer-complete You can use the @dfn{file name cache} to make it easy to locate a file by name, without having to remember exactly where it is located. When typing a file name in the minibuffer, @kbd{C-@key{tab}} (@code{file-cache-minibuffer-complete}) completes it using the file name cache. If you repeat @kbd{C-@key{tab}}, that cycles through the possible completions of what you had originally typed. (However, note that the @kbd{C-@key{tab}} character cannot be typed on most text-only terminals.) The file name cache does not fill up automatically. Instead, you load file names into the cache using these commands: @findex file-cache-add-directory @table @kbd @item M-x file-cache-add-directory @key{RET} @var{directory} @key{RET} Add each file name in @var{directory} to the file name cache. @item M-x file-cache-add-directory-using-find @key{RET} @var{directory} @key{RET} Add each file name in @var{directory} and all of its nested subdirectories to the file name cache. @item M-x file-cache-add-directory-using-locate @key{RET} @var{directory} @key{RET} Add each file name in @var{directory} and all of its nested subdirectories to the file name cache, using @command{locate} to find them all. @item M-x file-cache-add-directory-list @key{RET} @var{variable} @key{RET} Add each file name in each directory listed in @var{variable} to the file name cache. @var{variable} should be a Lisp variable such as @code{load-path} or @code{exec-path}, whose value is a list of directory names. @item M-x file-cache-clear-cache @key{RET} Clear the cache; that is, remove all file names from it. @end table The file name cache is not persistent: it is kept and maintained only for the duration of the Emacs session. You can view the contents of the cache with the @code{file-cache-display} command. @node File Conveniences @section Convenience Features for Finding Files In this section, we introduce some convenient facilities for finding recently-opened files, reading file names from a buffer, and viewing image files. @findex recentf-mode @vindex recentf-mode @findex recentf-save-list @findex recentf-edit-list If you enable Recentf mode, with @kbd{M-x recentf-mode}, the @samp{File} menu includes a submenu containing a list of recently opened files. @kbd{M-x recentf-save-list} saves the current @code{recent-file-list} to a file, and @kbd{M-x recentf-edit-list} edits it. The @kbd{M-x ffap} command generalizes @code{find-file} with more powerful heuristic defaults (@pxref{FFAP}), often based on the text at point. Partial Completion mode offers other features extending @code{find-file}, which can be used with @code{ffap}. @xref{Completion Options}. @findex image-mode @findex image-toggle-display @cindex images, viewing Visiting image files automatically selects Image mode. This major mode allows you to toggle between displaying the file as an image in the Emacs buffer, and displaying its underlying text representation, using the command @kbd{C-c C-c} (@code{image-toggle-display}). This works only when Emacs can display the specific image type. @findex thumbs-mode @findex mode, thumbs See also the Image-Dired package (@pxref{Image-Dired}) for viewing images as thumbnails. @node Filesets @section Filesets @cindex filesets @findex filesets-init If you regularly edit a certain group of files, you can define them as a @dfn{fileset}. This lets you perform certain operations, such as visiting, @code{query-replace}, and shell commands on all the files at once. To make use of filesets, you must first add the expression @code{(filesets-init)} to your @file{.emacs} file (@pxref{Init File}). This adds a @samp{Filesets} menu to the menu bar. @findex filesets-add-buffer @findex filesets-remove-buffer The simplest way to define a fileset is by adding files to it one at a time. To add a file to fileset @var{name}, visit the file and type @kbd{M-x filesets-add-buffer @kbd{RET} @var{name} @kbd{RET}}. If there is no fileset @var{name}, this creates a new one, which initially creates only the current file. The command @kbd{M-x filesets-remove-buffer} removes the current file from a fileset. You can also edit the list of filesets directly, with @kbd{M-x filesets-edit} (or by choosing @samp{Edit Filesets} from the @samp{Filesets} menu). The editing is performed in a Customize buffer (@pxref{Easy Customization}). Filesets need not be a simple list of files---you can also define filesets using regular expression matching file names. Some examples of these more complicated filesets are shown in the Customize buffer. Remember to select @samp{Save for future sessions} if you want to use the same filesets in future Emacs sessions. You can use the command @kbd{M-x filesets-open} to visit all the files in a fileset, and @kbd{M-x filesets-close} to close them. Use @kbd{M-x filesets-run-cmd} to run a shell command on all the files in a fileset. These commands are also available from the @samp{Filesets} menu, where each existing fileset is represented by a submenu. @ignore arch-tag: 768d32cb-e15a-4cc1-b7bf-62c00ee12250 @end ignore