Where can I access the EWS systems?
EWS maintains several labs on campus. A complete listing of these labs can be found at
http://www.ews.illinois.edu/labs/. Of particular interest is the lab located in L426 DCL.
In addition, it is possible to log in to the EWS systems remotely
using SSH or NX. Instructions on how to do so are located at
I can't log in. Who do I go to for help?
To access the EWS systems, you must have an active EWS account. All students in the College of Engineering
(i.e. most of you) already have these accounts. If you are not in the College of Engineering, contact one of the
course TAs about setting up an EWS account.
If you are a student in the College of Engineering, and you still
can't log in, first check that you are using the correct
password. Your password should be your Active Directory password.
To reset this password, visit the
CITES Password Manager web page.
If you know your AD password, and still cannot log on to the
system, contact EWS support at firstname.lastname@example.org.
Are there any UNIX tutorials I can read?
A few introductory tutorials for UNIX walkthrough are available
Washington University, the
Unversity of Utah and from Ohio
How do I set my PATH?
The syntax for setting your path is slightly dependent on which shell you
are using. Most people end up with a C-shellish shell (like tcsh or csh)
instead of a Bourne-ish shell (like sh, bash, ksh). If you aren't sure what
shell you are running, look at the output of either
To read all the particulars for setting environment variables you should
look at the man page for your shell (i.e. man bash for bash, or man tcsh
For Bourne like shells (bash, sh, ksh...), the syntax is:
For C-shell like shells (csh, tcsh...), the syntax is:
set path = ($path ~cs421/bin ~/bin)
means to keep the existing PATH and then append it with the other
These commands can either be typed at the terminal each time you login,
or you can add it to your .bashrc for bash shell or .cshrc for csh or
tcsh so that each time you login, the PATH is already set. After
modifying your .cshrc or .bashrc, you will need to either source it
or log out and log in again for your changes to take effect.
Please also note that if you're running tcsh, creating your own
.tcshrc will toss out a lot of EWS-specific setup in
.cshrc, so don't do that.
How do I download files quickly with wget?
When we make assignments, we sometimes include supplementary files,
whether it be actual source code or test input or output. These files may
be downloaded using standard browser techniques (by selecting "Save as"
or equivalent) or by using the wget program.
The program wget is available on the EWS machines where you are expected
to do your development. The wget program is a part of the GNU project.
UIUC has a mirror of GNU's FTP site as part of UIArchive.
To retrieve a file by its URL, the syntax is simply
To retrieve an entire directory of files, use
wget -r --level=1 the-url-pointing-to-the-directory
More options are available to wget; see wget -h.
How do I run a script I downloaded?
In the past, we have sometimes had students download scripts as
part of a project build. To be able to run a script requires
that what you have downloaded have the executable mode bit set,
which you would do with the command chmod. As an
example, let us say that you downloaded a script called
gen_output, and you needed to run it. You may
need to execute this chmod command before you are able to run
chmod u+rx gen_output
Of course, if you do not have "." on your path, to execute this script,
you may need to run the script like this:
As always, you should refer to the man pages for the commands that you
use. The man pages for wget and chmod are available on the EWS systems.
How do I use the CS 421 Piazza newsgroup?
CS 421 will use an external server hosted by Piazza
Technologies for newsgroup services this semester. To join
this service, please fill out
Once you have done this, you should be able to access the
service by going to https://piazza.com/class#fall2014/cs421.
On a specific MP, can we use functions we defined
in previous questions?
Unless we specify otherwise, the answer is yes.
Are we allowed to write helper functions?
As long as such helpers do not impede other requirements of the
question (such as requiring the solution, overall, to be tail
recursive), and as long as we don't specify otherwise; the answer