Added «mmv» to Files chapter

chapters/ch03-files.tex

@@ -10,6 +10,44 @@ fooabi.txt
 foo38r.txt
 \end{Verbatim}
 
+To remove the ``foo'', use this command:
+
+\begin{Verbatim}[]
+mmv 'foo*' '#1'
+\end{Verbatim}
+
+To change ``foo'' to ``bar'', use:
+
+\begin{Verbatim}[]
+mmv 'foo*' 'bar#1'
+\end{Verbatim}
+
+The \texttt{mmv} command uses this command structure:
+
+\begin{Verbatim}[]
+mmv [-m|x|r|c|o|a|l|s] [-h] [-d|p] [-g|t] [-v|n] [--] [from to]
+\end{Verbatim}
+
+For a full discussion of those, see the ``man'' page. The key concept here is that wildcard characters in the ``from'' option get replaced with ``\#1'', ``\#2'' etc in the ``to'' option, in the order they are encountered. So it is possible to reorder elements of file names. For example, to exchange ``foo'' in our list above for the file extension, we would use:
+
+\begin{Verbatim}[]
+mmv 'foo*.txt' 'txt#1.foo'
+\end{Verbatim}
+
+To reverse the order of the last three characters of the filenames, we would use:
+
+\begin{Verbatim}[]
+mmv 'foo???.txt' 'foo#3#2#1.txt'
+\end{Verbatim}
+
+That would produce this list of files:\index{mmv}
+
+\begin{Verbatim}[]
+foo341.txt
+fooiba.txt
+foor83.txt
+\end{Verbatim}
+
 \lettrine{T}{his} can also be accomplished by using the \textbf{rename}\index{rename} command.
 
 \section{Obtain a List of Files and their Paths}