HW1_WRITEUP,
containing the answers to the questions posed below.
classifieds directory you are asked to create.
cse230 in a
convenient place. Go to that directory, and create the
HW1_WRITEUP file. Then execute the following commands:
classifieds directory you made for Part II to your
cse230 directory. The second command will hand in
the HW1_WRITEUP file, together with the entire contents
of the classifieds directory.
man, too! This part of the assignment, doesn't require an extensive amount of hand-in. However, you shouldn't take a minimalist attitude toward it. Try to explore beyond the specific tasks I have given below. If you are already familiar with most of what is covered, treat the assignment as an opportunity to expand your knowledge.
passwd command. Read about
this command and use it.
.login and .cshrc)
.login and .cshrc in your home
directory are used by the C shell to initialize your working
environment. Check whether you have these files using
``ls -a''. (The -a option is required
to get ls to list files starting with ``.'', which
it normally does not list.) If you are a new user, you won't have
these files. Instead, you will automatically be using the system
defaults, which are in the files
NOTE: If you have copied .cshrc or
.login files from some other system,
I highly recommend that you remove them and start afresh.
Many ``problems'' that are reported to me are in fact caused by
people blindly copying .cshrc and .login
files from another system. The system defaults on the UG lab are
set up so that they are reasonable starting points for most users.
Do not add anything to your .cshrc or .login
file that you do not understand.
When you log in, the C shell executes these files in the following
order: first /etc/csh.cshrc, then
/etc/csh.login, then .cshrc in your home
directory (if it exists), and finally .login in your
home directory (if it exists). If the C shell is not running as
a ``top-level'' login shell, then it only runs the
/etc/csh.cshrc and .cshrc files.
Although there is a certain component of taste involved in what
you put in .cshrc and what you put in .login,
in general you have to put things that are not propagated to subshells
as part of the environment in .cshrc. All other stuff
should generally go in .login.
Put a line that reads simply:
.login, so that when you log in you will be
informed if there are any new messages to read.
.login file, using the setenv command
of the C shell.
The following is an example of commands to set some important
environment variables. These commands (or your own customized
versions) could be put in your .login file:
PATH environment variable
controls where the shell looks to try to find binary executables
for commands you type. The EDITOR variable states
which editor you prefer, and is consulted by some programs
(such as mailers) that start an editor. If you don't set this,
you will probably end up in vi (the default editor)
at some point. The PAGER variable determines which
program you prefer for paginating output to be viewed on a screen.
This is important for the correct operation of the man
command. The default pager is more. I prefer
less. (See section 3.6).
Other important environment variables are TERM, which
tells the official name of the type of terminal you are using,
and DISPLAY, which is used by X Windows programs to
determine which server (screen) to use as the display device.
QUESTION: From shell command level, execute the command:
ls.
Now try /bin/ls. In your writeup, explain the
results. You can recover from this situation by logging out
and logging back in again. In your writeup, describe a way to
recover that does not involve logging out.
Using the command which, find out the location
(full pathname) of the xterm command. Put it
in your writeup.
Using the printenv command of the shell, find out
what values you have set for the TERM and the
DISPLAY environment variables. Put them in your
writeup.
umask command:
umask command controls the default permissions
that files or directories will have when you create them.
By default, your umask is set to 022,
which means that write permissions are masked off for everyone
but you. However, this means that by default everyone on the system
will be able to read your files unless you take steps to prevent
them. Another common umask is 077,
which by default masks off all permissions for anyone other than you.
I recommend that you put the command:
.login file.
Try setting your umask to various values.
Then, create files or directories and use ls -l
and ls -ld to list them. Briefly explain the results.
du command:
du command can be used to find out how much
disk space you are currently using. Read the man page and try
it out.
QUESTION: How can one cause du to display
its information in units of kilobytes? How about in units of
512-byte disk blocks? In megabytes?
QUESTION: What is your disk quota?
Attempt to exceed your disk quota by making a number of copies
of a large file /usr/share/dict/web2 is convenient.
in your home directory. What happened to the last file you
tried to write? Now delete all the junk files from your
directory.
ls command (3.2):
ls command.
Find the simplest way you can to use ls to
determine all the files under your home directory and
any subdirectories that have been modified in the
last day.
cp command (3.4.3):
cp command is used to copy files from one place
to another on the system.
Find out how to use cp to copy the entire
hierarchy of files under your current directory
to /tmp.
grep command (4.2):
grep command is used to search for patterns in files.
Read about grep. Then find all the files in
the directory /usr/include (the C system header file
directory) that have occurrences of the string PATH_MAX
in them. To take advantage of the full power of grep, you need to understand about regular expressions (2.17). For now, though, you can limit your attention to using it to search for fixed-string patterns.
find command (3.8.1):
find command is extremely useful and powerful,
but has a syntax that is somewhat difficult for the neophyte.
Read about it. Then, construct a find command
to change the mode (protection) of all the regular files
under your home directory to mode 600
(read/write by you, no permissions to others).
Construct a find command to change the mode of all the directories
under your home directory to 700 (read/write/execute
by you, no permissions to others). Leave your home directory
with mode 755, otherwise X Windows won't work.
If the above commands were too easy, try to to construct a "find"
command to find all the regular files (not directories) under the
directory /var that have not been modified in one
week, and for each one to prompt you and ask if you want to view
that file using "more".
gzip and gunzip commands (3.13.2):
gzip command is used to reduce the space occupied
by a file by performing data compression on it.
The gunzip command uncompresses a previously compressed
file. Read about gzip, then try it out on various
kinds of files, including text files and binary executable files.
In general, what are the compression ratios for the various kinds
of files you tried? Make a copy of a text file, compress it,
then uncompress it, and use the diff command (3.10.2)
to check whether the result is identical to the original file.
/bin/sh)
shell scripts to be invoked by the World Wide Web server on
www.ug.cs.sunysb.edu in response to requests from clients on
the Internet. You will use the Common Gateway Interface (CGI)
standard for passing data from the client to the shell script. Your objective in this assignment and the next will be to construct a CGI-based system that permits clients on the Internet to read and post classified advertisements. For the moment, you will concentrate on displaying advertisements already online.
public_html of your home directory,
and to make sure that you have set ``world read and execute'' permissions
on it. If your user ID is fred, then when somebody on the Internet
attempts to access the URL of the form
www.ug.cs.sunysb.edu
(actually the same machine as public.ug.cs.sunysb.edu)
will respond by sending the file:
All files you wish to make available on the Web must have ``world read'' permission set. In addition, all directories the Web server must search to find these files must have ``world execute'' permission set.
To test out whether the Web server can access your public_html
directory, you may copy
this file and put it as Welcome.html under your
public_html directory.
Also create a subdirectory classifieds under your
public_html directory, and create a subdirectory
ads of classifieds.
Using a Web browser, access the URL:
In case something went wrong, you can likely get some information about what happened by looking at the Web server error logs. To view these, you have to log in on www.ug.cs.sunysb.edu and look at the files
less to view these files. You'll have to view near the
end of the file to see recent messages.
classifieds'' directory.
Make sure that ``world execute'' permission is set on both of the above
shell scripts.
If you have done this step properly, when you click on
the button leading to your classified ads project, instead of seeing
a directory listing, you will now see a form that looks like
this.
If you click on either READ or POST, then
if you have installed the select.cgi script properly,
you will see a message indicating that you have successfully
invoked the select.cgi script, and it will display for
you the arguments that were passed from the form.
Basically what happens when you click on the ENTER button,
is the Web server invokes the main.cgi shell script.
This script consists essentially of a bunch of echo
commands, which generate HTML code telling your Web browser to display
the form you see.
When you click on the READ or POST button
on this form, the Web server invokes the select.cgi script,
which again consists of echo commands to output HTML code
telling your browser to produce the display you see.
This time, though, the script uses the cgiparse command
to obtain information passed from the form and assign it to shell
variables. For example, within the select.cgi script,
the shell variable FORM_category variable has as its
value the menu item that was selected in the form.
select.cgi
script. For this assignment, you are to do two things:
main.cgi script so that, instead of
displaying a fixed list of categories in the menu,
it instead obtains the names of all subdirectories
of the directory classifieds/ads
and uses those names as the menu items instead.
Thus, if classifieds/ads has subdirectories
Automobiles and Computers,
these are the menu items that will be displayed in the
form.
select.cgi script so that, instead
of displaying the CGI arguments to the form, it interprets the
value of the FORM_category variable as the
name of a subdirectory of classifieds/ads,
it obtains a list of all the files in that subdirectory,
and then constructs and displays a list of hyperlinks to
those files.
For example, if the FORM_category variable
has the value Automobiles, and the
directory classifieds/ads/Automobiles contained
files 001, 002, and 003,
then your script should output HTML code like this: