Comprehensive System Administration

Lecture 8 notes:

Thanks to Steve Calahan for preparing this lecture.

administrivia:
        Enrollment
        Any problems?  Please email me to get on the course announcement list:
        jones@csua.berkeley.edu

        Getting Help
        If you have trouble, please email me, or one of the other teachers.
        The OCF staffers are often around the lab, and can be helpful.
        Don't forget your classmates can also be helpful.  

        Class Project

        The course project description is in Lecture 5.

        Questions?



class notes:

The Shell

The shell is what makes unix great.  Sure people will boast the stability,
but windows is getting to the point where is sucks to a much lesser extent
than in years past.  Others might say speed, but this is an abstract
concept, as what makes unix run faster on a lot of systems is that the
company which built the system, wrote the OS, and wrote it specifically to
run with that hard ware, giving them an "unfair" advantage.  There are
millions of other little advantages, better file systems, multi-user
capabilities, and remote access, but none of these are worth a damn without
the shell.
 The way that unix works is that the entire operating system
is run by a kernel.  The only way to talk to the kernel is through the
shell.  It is the gate keeper of all, your manner of communicating with the
machine, and what's beautiful about it is that the shell is a perfect
compromise of machine language and human contemplation.  One possibility
would be to compute everything using assembly commands, which the computer
understands immediately, but that sucks, especially since the language is
really ugly looks more like math than english, and I'm going to be stuck the
whole night programming in it.  The other option is to point and click your
way around like a monkey.  This is great for the average imbecile, but a lot
of the problems that occur with the stupidity of Windows users is that they
don't understand what is going on with the computer and the operating system
claims that they don't have to.  You click a button that is there and things
move, so when you need to learn how to do something new, you have little
idea where to look, and when something goes wrong, you certainly don't know
what happened.  
 The shell takes in commands in the same way that a
programming language interprets your code.  Lets use java because it's
popular and sexy:


java:

int number = 1;

number = number + 1;



 number now equals 2

shell:

let "number = (1)"

let "number = (number + 1)"



 number now equals2




Therefore all the commands that you have been taught to input into the shell
are better thought of as evaluations of the shell.  When you type at the
prompt something like:




bash$ cat letter.txt > spell



It will be evaluated by the shell in the following manner.


The shell will read first parse in this text and look for what is of highest
priority.  That is redirection.  The key strength of the shell is i/o input
and output.  It redirects information from one source to another.  The way
that your most familiar with is the redirection of information from the hard
drive to the monitor, or standard out.  (stout)  In this case the first
redirection to not is ">" it redirects the output of the first part of the
expression "cat letter.txt" into a program called spell, which which will
output this information to stout, which in this case will be the screen.





This one command will quickly spell check any document.  To do this with c
is a very annoying and difficult task.  I know this because the first
programming project for cs61c is philspell, and it's a really crappy spell
checker, depending on your library, but I won't get into that.  phil spell
was hundreds of lines of code for me.  On the other hand this was one line .
. .





OK, well I'm going into too much depth for notes.  After this I would
note that the shell is an ideal first language because so much can be done
in so little time.  Source to site, eye candy the window manager:




Why to make "eyecandy"

# /bin/bash



#EyeCandy --Calman

#Ooh boy this is gonna be cool

#oh so pretty!



nautilus &

if [-e /home/$USER/.eyecandy/custom] ; then

	sawfish /home/$USER/.eyecandy/custom &

else 

	sawfish 

fi



exec panel


homework

write "hello world"

write a shell script that prints out "hello world" if given no arguements,
and prints out "hello arguement" when given an arguement.

mail your script to jones@xcf.berkeley.edu