cd  <directoryname>           # change directory ("directory" is Linux-speak for "folder".) (".." means parent of current directory)
ls                            # lists files in current directory
ls -l                         # lists your files in 'long format' (size, who owns it, who can look at it, when last modified)
ls -lt                        # lists your files in order of modification time
ls -a                         # lists all files, including hidden files (whose name starts with a .)
more <filename>               # shows a file one screenful at a time (advance with spacebar and type q to quit)
less <filename>               # like more, only better (move with spacebar or up/down arrows)
head <filename>               # outputs the first lines of file (default 10)
tail <filename>               # outputs the last lines of file (default 10) (useful with -f option)
touch <filename>              # creates an empty file or updates timestamp
cat > <filename>              # places standard input into file (Ctrl-d to end)

mv <filename1> <filename2>    # moves or renames a file or directory (dangerous - see Aliases)
cp <filename1> <filename2>    # copies a file (dangerous - see Aliases)
rm <filename>                 # removes a file (dangerous - see Aliases)

nano <filename>               # lets you create and edit a file
diff <filename1> <filename2>  # compares files, and shows where they differ
wc <filename>                 # tells you how many lines, words and characters there are in a file
grep <pattern> <filenames>    # looks for the string in the files (asterisk can be used as a wild card in <filenames>)

chmod -options <filename>     # lets you change the read, write, and execute permissions on your files

history                       # prints all previous commands

<command1> | <command2>       # "pipe" the output of <command1> to the input of <command2>

alias <shorthand>="complicated command"

Aliases

Experienced users of bash typically have a large set of shorthands for complicated commands that they use frequently.

The alias commands that create these shorthands can be stored in a file called .bash_aliases in your home directory, and will be executed every time you start a bash shell. (Your home directory on this system is at /nsm/home/<username>. Note that your exam directory /exams_nsm/<username> is not your home directory, nor even in it.)

You navigate to your home directory by typing

cd

Among the aliases that you should absolutely positively have in your .bash_aliases are:

alias rm="rm -i"
alias cp="cp -i"
alias mv="mv -i"

These cause the commands rm, cp, mv to ask you for confirmation in cases where the operation could wipe something out. This is extremely important, because it is otherwise extremely easy to accidentally and instantly delete files (even a lot of files) - with no option of recovery.

Additionally you should include this command because the file system containing the Python 3 interpreter is, at the time of writing, not mounted by default on the server.

use python3

Other aliases or useful commands to be excecuted on startup are entirely up to you. The following might be useful:

alias me="cd /exams_nsm/<your user name>"

which will set the current working directory as your own exams directory.

The watermark script

To use this script, you need to provide 2 files in your own top-level exams folder: a PDF and your class roster.

Assuming you have already executed the "use python3" command either manually or automatically via your .bash_aliases, all you have to do is:

watermark exam.pdf roster.csv

where

exam.pdf - is the PDF of which watermarked copies will be made

roster.csv - is a csv file with a roster of students containing
        at least the following columns. (Other columns may be present if desired.)

        either "email" or "ubit"
                where email data is like "ringland@buffalo.edu" (must be @buffalo.edu)
                and "ubit" data is like "ringland"

        "PIN"
                which is an alphanumeric PIN that will be appended to the username
                in the names of the generated watermarked pdfs.

Optionally, you customize in a number of ways.

You can add a hexadecimal RGB color specification like this:

watermark exam.pdf roster.csv color=ffb0ff

to specify the page background color. A distinctive color like 00ffff will make life much easier for exam proctors.

The watermarked pdfs will be put in a folder whose name is the input pdf name with the ".pdf" extension removed, and a random string appended to make it unguessable. This folder will be created if it does not exist.

Other options for the watermark script are:

• choose your own password of 1 to 12 alphanumeric characters, BUT LETTERS MUST BE UPPERCASE:

watermark foo.pdf roster.csv color=00ffff password=MYOWNWORD3

• choose the darkness of the watermark (between 0 for invisible and 1 for totally black)

watermark foo.pdf roster.csv color=ff00ff markdark=0

These optional arguments (color=, password=, markdark=) can be supplied in any combination and in any order.

Instructors should note that the watermark layer is underneath the question text layer, so elements in your source document with an opaque background will mask the watermark.

Here is what a sample run looks like:

$ watermark pseudo-exam8.pdf 411_fake_roster.csv
Using fpdf for watermark creation
Using PyPDF2 for merging
['/usr/local/bin/watermark', 'pseudo-exam8.pdf', '411_fake_roster.csv']
Background color (255, 255, 0)
Watermark color (237, 237, 0)
Locking down pseudo-exam8.pdf
Locking down 411_fake_roster.csv
Added entry for this exam to lookup table
Watermarked pdfs will be in pseudo-exam8_f55272aee
Creating pdfs
        badzioch
        hassard
        jjfaran
        ringland


URL: https://exams.math.buffalo.edu

Password: PWQZET

The universal portal page https://exams.math.buffalo.edu is where students will go to obtain their individualized PDF with the exam questions by entering their username, PIN, and exam password:

If they enter invalid data, they will be bounced back to a similar page that has a predominantly yellow photo of the same scene.

For experts: "watermark" is a symbolic link in /usr/local/bin to the Python script /htdocs/www/exams_nsm/ringland/watermark.py.

%i% STEGWORDS ADD Summer probability

The individualize script

You build the exams with the command

individualize  my_first_exam.tex  my_student_roster.csv

Here is an example output, where the student "hassard" has binary code "11": you will see that the first two letters of all "Summer"s and "probability"s are in a discernably different font which is used to represent "1"s in the binary code.

Individualization markup

The idea is that in certain places that you identify with a string like "SUBfoo" or "SUBfoo[0]" or "SUBfoo[1]" you want to insert elements of a list, or "vector", of words or phrases that is chosen for each student from a list of possible vectors.

This list of vectors can either be given explicitly by you, such as

%i% {"foo":[ "l", ["chicken","pork"], ["meat","vegetable"], ["alcoholic","non-alcoholic"] }

("l" for explicit list) which will be substituted for "SUBfoo[0]" (first element of selected vector) and "SUBfoo[1]" (second element) in your latex source

or constructed as (optionally a subset of) the cartesian product ("cp") of sets of words and/or phrases that you provide such as

%i% {"bar":[ "cp", ["chicken","pork","beef"], ["Chinese","Indian","Italian","Vietnamese"], ["red","yellow","green","blue","violet"]] }

In this example, the list of generated vectors will have length 3x4x5 = 60, i.e. enough for each student in a class of 60 to have a unique vector, so that the text will uniquely identify the student.

For convenience, some pre-made lists are available, including: FEMALE_FIRST_NAMES (the 1500 most popular in the US in the year 2000), MALE_FIRST_NAMES (1500 also), CITIES (all the large cities in the world), RIVERS (6 or 7), PRIMARY_COLORS. Others could be added upon request.

In addition to the full cartesian product ("cp"), options are "restricted cartesian product" ("rcp") which means to select a vector from the cartesian product only if all its elements are distinct. This is useful, for example, in a case like

%i% {"2colors":[ "rcp", PRIMARY_COLORS, PRIMARY_COLORS ]}

you likely want each vector to have two distinct colors. There is also a "srcp" option in which each vector is internally sorted in lexicographic order

%i% {"2colors":[ "srcp", PRIMARY_COLORS, PRIMARY_COLORS ]}

so that you can be sure that if a student gets "green" and "red", the green will be SUB2colors[0] and the red (being later in the alphabet) will be SUB2colors[1].

Vectors are chosen sequentially from the list of vectors, so if the number of vectors is not less than the number of students, each student will get a distinct vector. Otherwise selection cycles repeatedly through the list of vectors.

Summary of markup codes

• l = list - sample vectors are chosen directly from the list you provide
• cp = cartesian product - sample vectors are chosen from the cartesian product of the sets you provide
• rcp = restricted cartesian product (only vectors with distinct elements are chosen)
• srcp = sorted restricted cartesian product (only vectors with distinct elements are chosen and vectors are internally sorted lexicographically)

Markup example

Here is an exerpt from a LaTeX source file:

%i% BEGINSCOPE
%i% {"she":["cp",FEMALE_FIRST_NAMES],
%i%  "8":["cp",["alpha","beta","gamma"],["1","2"] ],
%i%  "2":["cp",RIVERS],
%i%  "river":["rcp",RIVERS,RIVERS],  # restricted cartesian product - no replication of elements in any vector
%i%  "3":["l",["chicken","pork"],["meat","tofu"], ["meat","vegetarian"]], # want to select vectors from these pairs, use as SUB2[0], SUB2[1]
%i%  "4":["cp",CITIES],  # want to select pairs from the cartesian product
%i%  "5":["cp",MALE_FIRST_NAMES],
%i%  "6":["srcp",["red","orange","green"],["red","orange","green"]] } # want to select a pair from the cartesian product, except (x,x), sorted so (x,y) x<y.

SUBshe often likes to leave her hometown of SUB4 with her boyfriend SUB5
and go to a certain Chinese restaurant
at the confluence of the SUBriver[0] and SUBriver[1] rivers.
She always orders a different dish, either SUB3[0] or SUB3[1],
choosing randomly from the menu.
She has been there seven times.
If there are 17 SUB3[0] dishes and 16 SUB3[1] dishes,
and the first four of her choices were SUB3[0],
what is the probability that the other three dishes chosen by SUBshe were SUB3[1]?
%i% ENDSCOPE

Running the individualize script

Here is how to run the script:

individualize  my_first_exam.tex  my_student_roster.csv

And here is some sample output:

Verbose option: By default, output from pdflatex is hidden. In case you want to see this output, use the "-v" option:

individualize  my_first_exam.tex  my_student_roster.csv -v

If the script does not successfully run to completion, a good thing to try is see if your latex source itself is successfully compiled by pdflatex on the server:

pdflatex  my_first_exam.tex

Microsoft Word (.docx) source

The individualize script was written with LaTeX source in mind, but it will handle a source document in .docx format instead, if needed. (Note to experts: the individualize script actually hands off the job to a separate script individualize_docx.py that handles Word documents.)

Inserted images and formulas are preserved through the process (see below), but users are advised to visually check that these elements haven't changed position in a way that is not desired, and in general to keep the document simple - because I don't have the significant amout time it would take to write a totally robust processor for Word documents.

Steganography is not currently available with Microsoft Word source files.

chmod 700 testpdf/username_and_pin_eLZ5gfywvPuApwdyRps.html

chmod 755 testpdf/username_and_pin_eLZ5gfywvPuApwdyRps.html

Changing access to individual student exams

You can also use "chmod 700" to prevent access to any other individual file or folder. For example, if a particular student is taking an exam in a different mode (such as Zoom) or at a different time, you can "chmod 700" that student's exam, and then restore access by "chmod 755" whenever desired.