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<H4 ALIGN="LEFT"><A NAME="Heading8"></A><FONT COLOR="#000077">Undoing a Command</FONT></H4>
<P>In <TT>emacs</TT>, you can “undo” your most recent action or change to the buffer, as long as you have not saved that change to the disk file. You can undo by pressing <Ctrl-x><u>. By repeatedly using this command, you can undo the changes made to the buffer.</P>
<BLOCKQUOTE>
<P><FONT SIZE="-1"><HR><B>NOTE: </B><TT>emacs</TT> keeps track of the “undone” material first in memory buffers and then in a file, so theoretically you could undo every change you’ve made to a buffer up to the limits of your disk space. Practically, though, you’ll find the undo command useful for only the last few commands or edits you’ve done.<HR></FONT>
</BLOCKQUOTE>
<P>Unfortunately, you can’t use the undo command to undo writing something to a file as opposed to writing to the buffer.
</P>
<P>If you want to reread a file from disk (thus overwriting your current buffer changes), you can press <Ctrl-x><Ctrl-r>. This command reads the specified file into the current buffer, erasing its previous contents. Thus, if you specify the same filename, <TT>emacs</TT> replaces the current buffer with the contents of the file on disk. This is a quick way to undo many changes without exiting and restarting <TT>emacs</TT>.</P>
<P>But what if the <TT>emacs</TT> has autosaved the file or you’ve saved the file with unwanted changes? Well, <TT>emacs</TT> creates a backup file the first time you save a file, but not until you save the file. The name of this backup file is the same as the filename, except with a # character at the beginning and end of the name. Thus, if your file was named emacs-prtc.1, the backup filename is #emacs-prtc.1#. If you accidentally overwrite your current file with unwanted changes, you may be able to use the backup file to start over.</P>
<H3><A NAME="Heading9"></A><FONT COLOR="#000077">Writing Files and Saving the Buffer</FONT></H3>
<P>You’ve seen how to write the buffer to a file and quit <TT>emacs</TT>. Sometimes, however, you want to save the buffer to a file without quitting <TT>emacs</TT>. You should save the file regularly during an editing session. If the system goes down because of a crash or a power failure, you may lose your work if you haven’t saved it recently. To save the buffer, press <Ctrl-x><Ctrl-s>.</P>
<P>If you started <TT>emacs</TT> without specifying a filename, you must provide a filename if you want to save the file to disk. In this case, you press <Ctrl-x><Ctrl-s>, type the filename, and press <Return>.</P>
<P>You may want to save the buffer to a new filename different from the one you originally started with. For example, you start <TT>emacs</TT> with the file emacs-pract.1, make some changes to the file, and want to save the changes to a new file without losing the original emacs-pract.1 file. To save the file with a new filename, press <Ctrl-x><Ctrl-w>. <TT>emacs</TT> prompts you for the filename. The buffer is then written to the named file. If the command is successful, you see the name of the file.</P>
<P>If you specify the name of an existing file, a message appears in the mini-buffer, asking whether you want to overwrite the file. Simply answer the question appropriately.</P>
<H4 ALIGN="LEFT"><A NAME="Heading10"></A><FONT COLOR="#000077">Using Files</FONT></H4>
<P>If you want to load another file to edit, <TT>emacs</TT> can let you load a new file into the current buffer, or load a file into a new buffer, leaving the current buffer alone. <TT>emacs</TT> also lets you insert the contents of a file into the current buffer.</P>
<P>To replace the current buffer with the contents of another file, press <Ctrl-x><Ctrl-v>. <TT>emacs</TT> prompts for a filename in the mini-buffer. If you don’t remember the entire filename or if the name is rather long, you can use the completion option of <TT>emacs</TT>. When <TT>emacs</TT> prompts for a filename, you can enter just the first few letters in the name and then press <Tab>. <TT>emacs</TT> then expands the filename to match any files with those first few letters. If more than one file matches, <TT>emacs</TT> displays a window containing all the files matching the characters you entered and allows you to choose one.</P>
<P>To retrieve a file into a new buffer, press <Ctrl-x><Ctrl-f>. Enter the filename at the mini-buffer prompt. <TT>emacs</TT> normally names the buffer after the filename, but you can change the name of the buffer by pressing <Esc><x>, entering the new name for the buffer, and pressing <Return>. <TT>emacs</TT> prompts for the new name. Enter the new buffer name and press <Return>. The mode line displays the new name.</P>
<P>To insert a file into the current buffer, simply move the cursor to the desired position in the file and press <Ctrl-x><i>.</P><P><BR></P>
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