\section if if - Conditionally execute a command

\subsection if-synopsis Synopsis
<tt>if CONDITION; COMMAND_TRUE [else; COMMAND_FALSE] end;</tt>

\subsection if-description Description
<tt>if</tt> will execute the command CONDITION. If the commands exit
status is zero, the command COMMAND_TRUE will execute. If it is
not zero and COMMAND_FALSE is specified, COMMAND_FALSE will be
executed.

\subsection if-example Example

<pre>
if test -f foo.txt
	echo foo.txt exists
else
	echo foo.txt does not exist
end
</pre>
will print <tt>foo.txt exists</tt> if the file foo.txt
exists and is a regular file, otherwise it will print 
<tt>foo.txt does not exist</tt>.