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<TITLE>Linux Unleashed, Third Edition:Text Editors: vi and emacs</TITLE>
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<!--TITLE=Linux Unleashed, Third Edition//-->
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<P><BR></P>
<H4 ALIGN="LEFT"><A NAME="Heading10"></A><FONT COLOR="#000077">Starting vi</FONT></H4>
<P>You invoke <TT>vi</TT> from the command line by typing</P>
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<PRE>
vi
</PRE>
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<P>The screen clears and a column of tildes (<TT>~</TT>) appears in the leftmost column. You are now editing an empty, unnamed file. Whatever text you place in this file will exist in a buffer until you write the contents of the buffer to some named file. The tilde is <TT>vi</TT>’s way of telling you that the line where the tilde appears is empty of text.</P>
<TT>vi</TT> can also be started with a file or a list of files to edit:
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<PRE>
vi <I>filename1 filename2 filename3</I> …
</PRE>
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<P>Typically, you will probably edit only one file per <TT>vi</TT> session. If you are editing a list of files, <TT>vi</TT> edits each one in the sequence that they appear on the command line.</P>
<P>Alternatively, <TT>vi</TT> can be invoked from the command line as</P>
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<PRE>
vi +<I>n filename</I>
</PRE>
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<P>where <I>n</I> represents the line number where <TT>vi</TT> will place its cursor in <I>filename</I>. This is useful for programmers debugging large source code files who need to quickly jump to a known line containing an error.</P>
<P>Another example is useful in illustrating the <TT>vi</TT> editor. Enter</P>
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<PRE>
vi asong
</PRE>
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<P>at the command line and let’s see what happens.
</P>
<H4 ALIGN="LEFT"><A NAME="Heading11"></A><FONT COLOR="#000077">vi modes</FONT></H4>
<P>At the bottom of the screen in the left corner, you will see
</P>
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<PRE>
“asong” 0 lines, 0 characters
</PRE>
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<P>The messages that display on this status line tell you what <TT>vi</TT> is doing or has just done. In this case, <TT>vi</TT> is telling you that it has opened an empty buffer whose contents are saved (whenever you do a save) to the file <TT>asong</TT>.</P>
<P>At this moment, you are in the command mode of <TT>vi</TT>. This is the major conceptual leap required in working with this editor. When editing text, you must remember whether you are in command mode or text mode. In <I>command mode,</I> any character sequences that you enter are interpreted as <TT>vi</TT> commands. In <I>text mode,</I> every character you enter is placed in the buffer and displayed as text onscreen.</P>
<P>Four commands are echoed at the bottom of the screen on the status line:</P>
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<TABLE WIDTH="75%"><TR>
<TD WIDTH="25%">/
<TD WIDTH="75%">Searches forward
<TR>
<TD>?
<TD>Searches backward
<TR>
<TD VALIGN="TOP">:
<TD>An <TT>ex</TT> command (<TT>ex</TT> is a standalone line-based editor used within <TT>vi</TT>)
<TR>
<TD>!
<TD>Invokes a shell command
<TR>
</TABLE>
</CENTER>
<P>Each of these types of status-line commands must be entered by pressing Return. This is not true for other types of <TT>vi</TT> commands, such as the ones that do insertions.</P>
<BLOCKQUOTE>
<P><FONT SIZE="-1"><HR><B>Tip: </B><BR>To find out whether you are in command mode, use the <TT>set showmode</TT> preference described in the section, “Setting Preferences,” later in this chapter.
<HR></FONT>
</BLOCKQUOTE>
<H4 ALIGN="LEFT"><A NAME="Heading12"></A><FONT COLOR="#000077">Inserting Text</FONT></H4>
<P>So, knowing that you are in command mode, let’s insert some text. Basically, there are two commands for entering text on the current line: the letters <TT>i</TT> and <TT>a</TT>. These letters in lowercase insert (<TT>i</TT>) text to the left of the cursor or append (<TT>a</TT>) text to the right of the cursor. As with many <TT>vi</TT> commands, the uppercase versions of these letters have similar effects with subtle differences: uppercase <TT>I</TT> and <TT>A</TT> insert and append at the beginning and end of the current line, respectively, regardless of the cursor position.</P>
<P>After you type either of these letters, you are placed in input mode. Any text entered after this point is displayed onscreen.</P>
<P>Type an <TT>i</TT> and enter the following:</P>
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<PRE>
Down I walk<Enter>
by the bay,<Enter>
Where I can<Enter>
hear the water.<Enter>
Down we walk<Enter>
by the bay,<Enter>
My hand held<Enter>
by my daughter.<Enter>
</PRE>
<!-- END CODE SNIP //-->
<P>To exit from input mode, press Esc. Notice that the letter <TT>i</TT> does not display before you enter the text, meaning that the <TT>i</TT> was correctly interpreted as a command. Also, it is important to note that it is not necessary to press Return after pressing <TT>i</TT> for input mode.</P>
<H4 ALIGN="LEFT"><A NAME="Heading13"></A><FONT COLOR="#000077">Quitting vi</FONT></H4>
<P>Now that you have some text for your file, let’s quit the editor to see the results. The commands used for saving the file and exiting <TT>vi</TT> are slightly different from the <TT>i</TT> and <TT>a</TT> commands used in editing text; you must precede the command with a colon (<TT>:</TT>).</P>
<P>In this case, you want to do a save and exit, which are actually combined in one command. Enter<TT>:</TT> and a colon appears at the bottom left of your screen. <TT>vi</TT> has recognized that you are about to enter an <TT>ex</TT> command, and it will echo the remaining characters of the command after the colon. Type <TT>wq</TT> and press Return. <TT>vi</TT> quickly informs you that it has written the file to disk and tells you how many lines it contains. <TT>vi</TT> exits, and you find yourself back at the shell prompt. Another way to save and exit is to type <TT>ZZ</TT>. The difference between this method and using <TT>wq</TT> is that <TT>ZZ</TT> writes the file to disk only if it has been modified since the last save.</P>
<P>If no changes have been made to the file you opened, you quit <TT>vi</TT> by simply typing <TT>:q.</TT> This does not work if the file has been modified. If you are sure that you don’t want to save what you have done, enter <TT>:q!</TT>. This command forces <TT>vi</TT> to quit, regardless of any edits.</P>
<P>To make sure that <TT>vi</TT> saved the file <TT>asong</TT> correctly, use the <TT>cat</TT> command to quickly view the file’s contents:</P>
<!-- CODE //-->
<PRE>
% cat asong
Down I walk
by the bay,
Where I can
hear the water.
Down we walk
by the bay,
My hand held
by my daughter.
%
</PRE>
<!-- END CODE //-->
<P>Everything is exactly as you typed it in the file, so no surprises here.
</P><P><BR></P>
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