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\author{Piyush P Kurur\\
  Office no: 224\\
  Dept. of Comp. Sci. and Engg.\\
  IIT Kanpur}


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\title{Fundamentals of Computing: Lecture 37}
\date{November 9, 2009}
\begin{document}
\begin{frame}
  \maketitle
\end{frame}

\begin{frame}
  \frametitle{The Unix system}
  \begin{tikzpicture}
    \node[oval,fill=yellow!30]{
      \begin{tikzpicture}[node distance=0pt]
        \node(shell){shell};
        \node[oval, fill=yellow!40, below=of shell]{
          \begin{tikzpicture}
            \node(user){user programs};
            \node[oval, fill=red!30, below=of user]{
              \begin{tikzpicture}
                \node(kernel){kernel};
                \node[oval, fill= red!40, below=of kernel]{hardware};
              \end{tikzpicture}
            };
          \end{tikzpicture}
        };
      \end{tikzpicture}
    };
  \end{tikzpicture}


\end{frame}
\begin{frame}
  \frametitle{The Shell}
  \begin{itemize}
    \pause
  \item The command processor
    \pause
  \item In non-graphical mode is the first that is executed on login.
    \pause
  \item Is programmable.
    \pause
  \item Collection of shell commands forms a shell program.
  \end{itemize}
  
  \pause
  \begin{block}{Which shell?}
    \pause 

    There are many shells available, each slightly different syntax.

    We will use the |bash| shell. Other common shells are |csh|, |zsh| etc.
  \end{block}

\end{frame}

\begin{frame}
  \frametitle{Simplest shell program}
  The starting |$| is the prompt. You dont have to type it.
  \begin{spec}
   $ programname arg1 arg2 arg2
  \end{spec}
  e.g.
  \begin{spec}
   $ echo foo bar biz
  \end{spec}

\end{frame}

\begin{frame}
  \frametitle{Redirecting a file to input and output to file}
  Remember that every program has three open files,
  |stdin|, |stdout|, |stderr|
  \begin{itemize}
  \item If we write |$ cmd <foo| then the |stdin| of |cmd| is
    the file |foo| and not the keyboard.
  \item If we write |$ cmd >foo| then the |stdout| of |cmd| is
    the file |foo| and not the monitor.
  \end{itemize}
  
  \begin{spec}
$ cat > foo
I am redirecting the output of cat to foo.
$ cat < foo
I am redirecting the output of cat to foo.
$ exit
  \end{spec}
\end{frame}
\begin{frame}
\frametitle{One can also redirect |stderr|}

\begin{itemize}
  \pause
\item Redirecting |stderr| to a file   |cmd 2>foo| (no space between |2| and |>|)
  \pause
\item Redirecting |stderr| to |stdout| |cmd 2>&1|(no space between |&| and |1|)
\end{itemize}

\pause
\begin{spec}
  $ gcc badCFile.c 
  # Too much data  see in pages
  $ gcc badCFile 2>&1 | less
\end{spec}

\pause

This also tells us about piping.

\begin{spec}
  $ cmd1 | cmd2 | cmd3 | cmd4
  $
\end{spec}

\end{frame}

\begin{frame}
  \frametitle{Some useful programs}
  \begin{itemize}
  \item |echo| prints its command line arguments
  \item |less| shows int |stdin| in pages
  \item |grep pattern| shows only those lines of its stdin 
    that matches the pattern.
  \end{itemize}
\end{frame}

\end{document}