Caveat Lector: These are some notes for a basic course on Unix which I co-taught many years ago at the University of Calgary. I keep them online in the hope that they may be useful to someone. However, they are not maintained. They may contain information specific to one (historic) network, which will not apply universally. Links may be broken.

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Computer Science 001

Introduction to Unix

September 1998

Part Two

Shell scripting:

An Example Shell script:

#! /bin/csh -f

# must have at least one argument on the command line

if ($# < 1) then

    cat <<EOF;
    Usage:
            $0:t [argument]+

EOF
exit

endif

# x becomes the number of command line arguments
set x = $#

# print out info on the command line arguments

while ($x > 0)

    echo "=========== $1 ==============="
    if ( -e /home/staff/dutton/$1) then
        echo "Exists in /home/staff/dutton"
        if ( -r /home/staff/dutton/$1) then
            echo "and is readable"
        else
            echo "but is not readable"
        endif
        if ( -w /home/staff/dutton/$1) then
            echo "and is writeable"
        else
            echo "but is not writeable"
        endif
    else
        echo "Does not exist in /home/staff/dutton"
    endif

## determine the system we are on
## useful in a .cshrc file

    switch ("`uname -a`")
    case IRIX64*:
        echo "You're on and Irix 6.4 machine"
        breaksw
    case IRIX*:
        exho "Your on an Irix 5.3 machine"
        breaksw
    case SunOS*4\.1*:
        echo "You're on a SunOS machine"
        breaksw
    case SunOS*5\.*:
        echo "You're on a Solaris machine"
        breaksw
    case Linux*:
        echo "You're on a Linux machine"
        breaksw
    default:
        echo "You're not on our system"
        breaksw
    endsw

@ x--
shift # shifts argv to the left one place
end

foreach i ( `/bin/ls `)
    if ( ! -d /home/staff/dutton/oo1/$i) then           # if it's not a d
irectory
    ## print some info on it (notice the back ticks)
    /usr/bin/file   /home/staff/dutton/oo1/${i}
    endif
end

some sample output...

dutton@coral:oo1>./cshdemo
Usage:
cshdemo [argument]+

dutton@coral:oo1>!!
./cshdemo one
=========== one ===============
Does not exist in /home/staff/dutton
You're on a Linux machine
/home/staff/dutton/oo1/#outline#: ASCII text
/home/staff/dutton/oo1/Daytwo: HTML document text
/home/staff/dutton/oo1/Notes: HTML document text
/home/staff/dutton/oo1/cshdemo: C shell script text
/home/staff/dutton/oo1/kernel-2.0.35-2.i386.rpm: RPM v3 bin i386 kernel-2.0.35-2
/home/staff/dutton/oo1/manpage: English text
/home/staff/dutton/oo1/outline: HTML document text
/home/staff/dutton/oo1/source.tar: GNU tar archive
/home/staff/dutton/oo1/webmin-0.54.tar.gz: gzip compressed data, deflated, original filename, last modified: Thu Jul 2 06:24:32 1998, os: Unix
/home/staff/dutton/oo1/xmeter: sparc demand paged dynamically linked executable

dutton@coral:oo1>./cshdemo .cshrc .login .logout
=========== .cshrc ===============
Exists in /home/staff/dutton
and is readable
and is writeable
You're on a Linux machine
=========== .login ===============
Does not exist in /home/staff/dutton
You're on a Linux machine
=========== .logout ===============
Does not exist in /home/staff/dutton
You're on a Linux machine
/home/staff/dutton/oo1/#outline#: ASCII text
/home/staff/dutton/oo1/Daytwo: HTML document text
/home/staff/dutton/oo1/Notes: HTML document text
/home/staff/dutton/oo1/cshdemo: C shell script text
...

A closer look at the script:

#! /bin/csh -f

Tells the Operating system which program to use to execute this script
In this example it's csh
the -f says don't bother reading the .cshrc, etc files
other scripting choices might use..

#! /bin/sh
#! /usr/local/bin/perl
#! /bin/ksh
#! /usr/local/bin/tcsh

if ($# < 1) then

    cat <<EOF;
    Usage:
            $0:t [argument]+

EOF
exit

Demonstrates and if statement csh programming
$# refers to the number of command line arguments and is equivalent to $#argv
this section checks to see there are any arguments and if not cat's a usage message. The <<EOF just means keep catting till you see the label EOF
$0 refers to the first command line entry, ie the name of the script itself.
the :t on the $0 says only give me the tail of the entry. It has the effect of chopping off the rest of the path

set x = $#

Demonstrates how to set a variable in csh programming
other examples...

set y = "Hello there " ## set a string
set z = ` ls -l ` ## the results of the ls
set a= y."there" ## concat "there" onto y and store in a

this example sets x to the length of $argv

while ($x > 0)

...

end

Demonstrates a while loop in csh programming
in this case the while loop will decrement x inside the loop ( @ x-- statement)

if ( -e /home/staff/dutton/$1) then

echo "Exists in /home/staff/dutton"

if ( -r /home/staff/dutton/$1) then

echo "and is readable"

else

echo "but is not readable"

endif

if ( -w /home/staff/dutton/$1) then

echo "and is writeable"

else

echo "but is not writeable"

endif

else

echo "Does not exist in /home/staff/dutton"

endif

A more complicated example of an if then else statement
each else, or elseif goes with the closest if
-e, -r, -w are self explanatory. Other such tests can be found on the "sh" man page. Do "man sh"

switch ("`uname -a`")

case IRIX64*:

echo "You're on and Irix 6.4 machine"

breaksw

case IRIX*:

exho "Your on an Irix 5.3 machine"

breaksw

case SunOS*4\.1*:

echo "You're on a SunOS machine"

breaksw

case SunOS*5\.*:

echo "You're on a Solaris machine"

breaksw

case Linux*:

echo "You're on a Linux machine"

breaksw

default:

echo "You're not on our system"

breaksw

endsw

Demonstrates a switch statement in csh
In this example, each case statement use "*" as a pattern matching character.
Capitalization matters here
default mathes everything not matched by the other cases
When a case is matched the statements following (up to the next breaksw or endsw) are executed

This switch is order dependant (which is usually a very bad idea)
the '\' characater is used to escape characters that may have special meaning to the shell

foreach i (`/bin/ls `)

if ( ! -d /home/staff/dutton/oo1/$i) then # if it's not a directory

## print some info on it (notice the back ticks)

/usr/bin/file /home/staff/dutton/oo1/${i}

endif

end

Demonstrates the for loop in csh programming
each iteration sees i take on the next value from the list
the value of i (or any variable) can be used by preceeding it with $
{} can be used so that the variable name is not confused in context

example: $iou would be interpreted as a variable named iou
${i}ou is the variable i followed by ou

The script ends when it runs out of statements, or when it encountes an exit
loops, such as the while loop can contain a built in command called "continue" which would
have the effect of going to the next iteration of the loop ignoring all statements in the loop which
follow the continue
loops, such as the while loop can contain a built in command called "break" which have the effect of
breaking the loop and continuing the program execution at the statement immediately following the loops end
Example:
#!/bin/csh -f

set x = 1

while ($x >= 1)

        if ($x == 3) then
                @ x++
                continue
        endif
        if ($x == 5) then
                break
        endif
        echo "Loop iteration $x"

@ x++
end

echo "End of script"

output of % ./cshdemo2

Loop iteration 1
Loop iteration 2
Loop iteration 4
End of script

Emacs and Vi:

Good resource site: http://www.geek-girl.com/emacs/

vi

Some programs use vi as their default editor. To get out of vi, type :q and press enter. If you want to be a sysadmin, read the vi man page. Otherwise, you might want to
setenv EDITOR emacs

(excerpts from the) GNU Emacs Reference Card

Starting Emacs

start editor                                       emacs
edit 'myfile'                                      emacs myfile
edit 'myfile', put cursor on line 12               emacs myfile +12

Leaving Emacs

suspend Emacs (or iconify it under X)              C-z
exit Emacs permanently                             C-x C-c

Files

read a file into Emacs                             C-x C-f
save a file back to disk                           C-x C-s
insert contents of another file into this buffer   C-x i
write buffer to a specified file                   C-x C-w

In the Minibuffer (the bottom line of the screen), pressing TAB will complete the filename/command you are typing, or show you a list of possible completions.

Getting Help

You might be able to use F1 insead of C-h.

tutorial                                           C-h t
apropos: show commands matching a string           C-h a
show the function a key runs                       C-h k
describe a function                                C-h f
read "info" pages                                  C-h i
when you can't find your answer anywhere else      M-x doctor

Error Recovery

abort partially typed or executing command         C-g
undo an unwanted change                            C-x u or C-`
redraw garbaged screen                             C-l

Incremental Search

search forward                                     C-s
search backward                                    C-r
repeat last search                                 C-s C-s
repeat last search backwards                       C-r C-r
goto line XX                                       M-x goto-line

Motion

entity to move over                        backward      forward

character                                  C-b           C-f
line                                       C-p           C-n
screen                                     C-v           M-v
go to line beginning (or end)              C-a           C-e
go to buffer beginning (or end)            M-<           M->

Killing and Deleting

character delete                                   DEL or C-d
kill (to end of) line                              C-k

set mark here                                      C-@ or C-SPC
exchange point and mark                            C-x C-x

kill region                                        C-w
copy region to kill ring                           M-w
yank back last thing killed                        C-y
replace last yank with previous kill               M-y

To kill 5 lines, pass a numeric argument to the kill function:
M-5 C-h

Query Replace

interactively replace a text string                M-%

At each occurrance you will be asked if you really, really want to replace. Answer either y or n, or press ! to replace all.

Multiple Windows

delete all other windows                           C-x 1
split window in two                                C-x 2
switch cursor to another window                    C-x o

Buffers

select another buffer                              C-x b
list all buffers                                   C-x C-b
kill a buffer                                      C-x k

Keyboard Macros

start defining a keyboard macro                    C-x (
end keyboard macro definition                      C-x )
execute last-defined keyboard macro                C-x e

Modes

Emacs has a number of modes which make it handy for programming. E.g. in C mode, the tab character will indent the line as appropriate to the depth of your nested loops/if statements. To change mode, use M-x XXXX-mode where XXXX can be C, java, html, etc.

Special Characters

To enter a control character in your file (say, ^H) prepend it with C-q.

Guru Stuff

On many keybords, the backspace key returns the same sequence as C-h, which can be annoying. To change the binding of a key, (say, C-h, to be backspace,) use
M-x global-set-key, then press the key (the backspace key), and then name the function which you would like to bind to it (in our case, delete-backward-char). You may then have to run the 'help' command by typing M-x help, or you can rebind this to another key. To check what function a key is bound to, use C-h k followed by the key. A good place for key bindings is in Emacs' initialization file, .emacs. Mine contains things like:

;; The following line of code allows the BACKSPACE key to be used
;; as the DELETE key.
(define-key global-map "\C-h" 'delete-backward-char)

;; The following line defines C-c C-h to get help.
;; Normally the BACKSPACE key is used for help.
(define-key global-map "\C-c\C-h" 'help-for-help)

;; make f8 the goto-line key
(global-set-key [f8] 'goto-line)

;; show what line number you're on at the bottom of the screen
(setq line-number-mode t)

.emacs can also be used to change to fonts/colours for comments or strings in your programs. For an example see ~rf/.emacs

           Copyright c 1993 Free Software Foundation, Inc.
              designed by Stephen Gildea, May 1993 v2.0
              for GNU Emacs version 19 on Unix systems
Permission is granted to make and distribute copies of this card provided the 
copyright notice and this permission notice are preserved on all copies.
For copies of the GNU Emacs manual, write to the Free Software Foundation, 
Inc., 675 Massachusetts Ave, Cambridge MA 02139.

Makefiles and Compiling:

See the makefile example in the mf/ directory. The file mf.run is the output generated by some of the scripts in the file.

Common Compiling Problems:

use tabs at the beginning of lines in Makefiles!

make: *** File `life.c' has modification time in the future

means that the clocks of the NFS and your workstation are out of sync
no big deal most of the time
if it is a big deal, compile in /tmp

make: *** No rule to make target `life.h', needed by `life.o'. Stop.

one of the rules references a header file that does not exist
create the file, or take it out of the rule

make: `life' is up to date.

make doesn't think the file needs to be recompiled
remove the binary or touch one of the .c or .h files

You try to run the program, but it's either not found or does something completely different.

run it as ./a.out
look at your $PATH; chances are that the system is looking in the wrong dir

Compilation doesn't give any errors, but ld complains about unresolved symbols.

you've forgotten a #include header or to link in a library with -l
a common one is the math library, -lm
the man page of the unresolved symbol might give clues as to the library to use

ld.so complains about not being able to load yadda_yadda.so.6.3 (or something like that)

.so files are dynamically loaded libraries (.DLL in Windoze)
adjust your $LD_LIBRARY_PATH to include the directory containing the .so

The program you compiled at 1:00 am last night won't run this morning.

make sure that you are running on the same architecture & OS
use the command 'uname -s -r' to find out what sort of machine you are on
locations of header files, sizes of variables, etc. differ from OS to OS!

Your program had a seg fault and now emacs says that you've exceeded your disk quota and won't save your file.

look for a file called 'core' in your directory & remove this
core files are images of memory when your program died; hence they are large
you can look at a core file using your favourite debugger

Setting up your Web Page:

Setting up your directory

create a directory called "www" in your home account

cd ~; mkdir www

Set up proper permissions on it

cd ~; cd www; chmod 711 .

All web files should live in this directory and should be world readable
your main page should be called index.html as this is what is automatically looked for by many browsers when they come to your URL

HTML tutorial/ Web page resources are available at may sites on the web. One I particularily like is .. http://www.pageresource.com/html/index.html
If you're not interested in learning HTML, but do want a web page then you can use
a web page editor, such as Netscape Communicator to create your page.
your URL will be "http://www.cpsc.ucalgary.ca/~login_name_goes_here

replace login_name_goes_here with your actual log in name.

CGI (common gateway interface) is not available to undergraduate students in the department
of computer science
We have Netscape and Lynx available as browsers for undergraduate students
The departments Web page is at http://www.cpsc.ucalgary.ca. Your should have a look at it as it contains some
useful information, including links to the courses home pages, links to prof home pages and HELP pages.