@comment  node-name,  next,  previous,  up
@node Files, Other Customizations, Modes, Top
@chapter Files
@cindex files

   The basic unit of stored data in Unix is the @dfn{file}.  To edit a file,
you must tell Emacs to read the file into a buffer. This is called
@dfn{visiting} the file. You can now edit the buffer and to save the
changes you must write the buffer back to the file.  

  In addition to visiting and saving files, Emacs can delete, copy, rename,
and append to files, and operate on file directories.

@comment  node-name,  next,  previous,  up
@menu
* File Names::                  How to type and edit file name arguments.
* Visiting::                    Visiting a file prepares Emacs to edit the file.
* Saving Files::                How to save Emacs files.
@end menu

@node File Names, Visiting, Files, Files
@section File Names
@cindex file names

   Most of the Emacs commands that operate on a file require you to
specify a file name. For example, you might specify the file name
initially when you enter Emacs :

@example
xemacs myfile RET
@end example

@noindent
After you hit @key{RET}, you will enter XEmacs with "myfile" read into
the current buffer. If you do not specify the filename when entering
Emacs, you can use the @b{Open...} option from the @b{File} menu. You
will be prompted for a filename in the echo area:

@example
Find file: /usr/workspace/
@end example

@vindex default-directory
@noindent
Type in a file name which you want to open after the "/" and hit
@key{RET}. The specified file will be read into the current buffer. The
"/usr/workspace" might be the @dfn{default directory}. When Emacs
prompts you for a file, it uses the default-directory unless you specify
a directory. You can see what the default directory of the current
buffer is by using the @b{Describe Variable} option from the @b{Help}
menu. When Emacs prompts you for the variable name to describe, type
@var{default-directory}. If you wish to open a file in some other
directory, use @key{DEL} or the @key{BackSpace} key to go back and type
the path name of the new directory. 

   You can create a new directory by typing @kbd{M-x
make-directory}. This command will prompt you for a directory name:

@example
Create directory: /usr/workspace/
@end example

@findex make-directory
@findex remove-directory
@cindex creating-directories
@cindex removing-directories
@noindent
After you type a directory name and press @key{RET}, a new directory
with the specified name will be created. If you do not wish to create a
new directory, then simply press @kbd{C-g} to quit the
command. Similarly, you can also remove a directory by using the command
@kbd{remove-directory}. The command @kbd{M-x pwd} will print the current
buffer's default directory. For more information on file names,
@xref{File Names,,,,XEmacs Reference Manual}.
 

@node Visiting, Saving Files, File Names, Files
@section Visiting Files
@cindex visiting files

   To edit a file in Emacs you need to @dfn{visit} it. @dfn{Visiting} a
file means copying its contents (or reading them) into the current
buffer. Emacs will create a new buffer for each file that you visit. The
buffer will be named after the file that you open. If you open a file
@file{/usr/workspace/myfile.texinfo}, the buffer will be called
"myfile.texinfo". If a buffer with this name already exists, a unique
name will be constructed by appending @samp{<2>}, @samp{<3>}, etc. If
this is the second buffer with the same name, a "<2>" will be appended,
"<3>" for a third buffer and so on. The name of the buffer which is
being displayed in the window will be shown both at the top and bottom
of the frame. Once you are in XEmacs, you can use the following
commands:

@table @kbd
@item C-x C-f
@findex find-file
@kindex C-x C-f
This command will visit a file (@code{find-file}). It will prompt you
for a file name to visit. The @b{Open...} option from the @b{File} menu
does the same thing:

@example
Find file: /usr/workspace/
@end example

@noindent
Type in a filename and press @key{RET}. You will see a new buffer on the
screen with its name in the mode-line. If the filename you specify
already exists in Emacs, the buffer containing that file will be
selected. You will get an error message if the filename does not
exist. If you still press @key{RET}, a new buffer with the given
filename will be displayed on the screen.  

@item C-x C-v
@kindex C-x C-v
@findex find-alternate-file
This command (@code{find-alternate-file}), will visit a different file
instead of the one visited last. It is similar to @kbd{C-c C-f} except
that it kills the current buffer (after offering to save it). 

@item C-x 5 C-f
@kindex C-x 5 C-f
@findex find-file-other-frame
This command will visit a file in another frame
(@code{find-file-other-frame}) without changing the current window or
frame. The @b{Open in New Frame...} from the @b{File} menu will do the
same thing. It will prompt you for a file name in the echo area. After
you type the file name and press @key{RET}, the specified file will be
read into a new buffer and displayed on a new frame. 
@end table

@node Saving Files,  , Visiting, Files
@section Saving Files
@cindex saving files

   The changes that you make after visiting a file will not be saved
unless you save the buffer. When you save the buffer, Emacs writes the
current contents of the buffer into the visited file. Some commands to
save buffers are:

@table @kbd
@item C-x C-s
@findex save-buffer
@kindex C-x C-s
This command will permanently save the current buffer in its visited
file (@code{save-buffer}). You will see the following message in the
echo area if you save a file called "myfile.texinfo" :

@example
Wrote /usr/workspace/myfile.texinfo
@end example

@noindent
Try using this command twice. You will get the above message the first
time you use this command, the second time you will get the following
message: 

@example
(No changes need to be saved)
@end example

@noindent
This message indicates that you haven't made any changes since the last
time you saved the file. 

@item C-x s
@kindex C-x s
@findex save-some-buffers
This command will save all the buffers in their visited files
(@code{save-some-buffers}). It will prompt you for typing yes or no:

@example
Save file /usr/workspace/myfile.texinfo? (y or n)
@end example

@noindent
You will get the above message for all the buffers. Type "y" if you want
to save the buffer. 

@item C-x C-w
@findex write file
@kindex C-x C-w
This command will prompt you for a file name and save the current buffer
in that file. (@code{write-file}). You will see the following message in
the echo area:

@example
Write file: /usr/workspace/
@end example

@noindent
After you type in a file name, press @key{RET}. The buffer will be saved
in a new file. You can make copies of a particular file using this
command. 
@end table

   You can also undo all the changes made since the file was visited or
saved by reading the text from the file again (called
@dfn{reverting}). For more information on this option,
@xref{Reverting,,,,XEmacs Reference Manual}. 

@vindex make-backup-files
   When you save a file in Emacs, it destroys its old contents. However,
if you set the variable @var{make-backup-files} to non-@var{nil}
i.e. @samp{t}, Emacs will create a @dfn{backup} file. Select the
@b{Describe variable} option from the @b{Help} menu and look at the
documentation for this variable. Its default value should be
@samp{t}. However, if its not then use @kbd{M-x set-variable} to set it
to @samp{t} (@pxref{Setting Variables}). The backup file will contain
the contents from the last time you visited the file. Emacs also
provides options for creating numbered backups. For more information on
backups, @xref{Backup,,,,XEmacs Reference Manual}. 

@cindex auto saving
   Emacs also saves all the files from time to time so that in case of a
system crash you don't lose lot of your work. You will see the message
@samp{Auto-saving...} displayed in the echo area when the buffer is
being saved automatically. The auto saved files are named by putting the
character @samp{#} in front and back. For example a file called
"myfile.texinfo" would be named as @file{#myfile.texinfo#}. For
information on controlling auto-saving and recovering data from
auto-saving, @xref{Auto Save Files,,,,XEmacs Reference Manual}. 

@cindex simultaneous editing
   Emacs provides protection from simultaneous editing which occurs if
two users are visiting the same file and trying to save their
changes. It will put a lock on a file which is being visited and
modified. If any other user tries to modify that file, it will inform
the user about the lock and provide some
options. For more information on protection against simultaneous
editing, @xref{Interlocking,,,,XEmacs Reference Manual}.

   

   



















