CS2043 Assignment 4 Solution

CS2043 Assignment 4 
General Note: This assignment (and future ones) require you to have access to a
Unix-like (Linux, Mac OS X, etc) machine. If you do not have such an operating system
installed on your local machine, make sure to get a CSUG Lab account. Different systems have slightly different configurations. The main environment in this class is GNU/Linux.
Assignment Notes:
− You must complete the assignment using tools that were discussed in class.
− This assignment is composed of two parts.
− For each problem, you will write a script (not the output thereof), and save it to a file
named with the specified problem label
e.g. problem1name.sh or problem1name.py.
Assume that the input is in the same directory as the script.
A bash script is a text file with: #! /bin/bash
A python script is a text file with: #! /usr/bin/python
as the first line.
− Please also include a short README file with some feedback on the assignment.
− Remember to start this assignment early.
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CS2043 Assignment 4 February 22, 2015
Email Reminder
Create a file called myweekly act.txt that describes your weekly activities using the
following format:
Mon : List of activities for Monday
Tue : List of activities for Tuesday
Wed : List of activities for Wednesday
Thu : List of activities for Thursday
Fri : List of activities for Friday
(replace ”List of activities for...” with your weekly tasks for that day)
act reminder.sh: Write a script that sends you an e-mail whose subject is ”Reminder:
Tasks for today” and whose body contains your tasks for the day in which you run
the script using myweekly act.txt as input, i.e., on Mondays, it will send you the
task for Monday, on Tuesdays, the tasks for Tuesday, and so on. Please do not include
myweekly act.txt in your submission.
remind daily.txt: We want to program the computer to remind us of our everyday tasks
by e-mail. Write a crontab line (not a shell script) in the file remind daily.txt that is
going to make the system execute act reminder.sh automatically every weekday (Mon-Fri)
at 6:00AM.
The date command prints today’s date. We can use its user-defined formatting options to
extract what we want from its output (see man date) or parse its output using other tools.
You can send the output of a command via e-mail by redirecting its output to:
mailx [-s "subject"] <e-mail address
mailx is not easy to configure, but it is already configured and ready to use on the CSUG
Lab machines and on the VM images (you need to be connected to a Cornell network for
mailx to work if you are using a VM).
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CS2043 Assignment 4 February 22, 2015
My ebook reader
Your objective in this part is to write a python script, ereader.py that is a rudimentary
“plain-text eBook reader”. The idea here is that a user would launch this program, read a
little bit of a book and close it. Next time the user launches this program with that book,
he continues from where he left off the last time.
The script takes at least one command-line argument, the name of the file to open. The
user can also supply an optional paging argument identified by the flag -n that dictates how
many lines to display per page. If the user did not supply that argument, the script should
assume a default paging of 40 lines per page. Finally, for navigation, we will only support
three operations: “next page”, “previous page”, and “quit”. The next page is displayed when
the user presses the n key, the previous page is displayed when the user presses the p key,
and the application quits when the user presses the q key.
To make things simple, here is how we’re going to make the script work:
1. When the script starts, it checks to see if the user’s home directory contains a
∼/.reader_rc file (the filename starts with a dot). We will use this file to store the
progress of different files. So if the home directory does not contain a ∼./reader_rc
file, we will create one.
2. The contents of a .reader_rc file will be a two comma-separated columns of
file_content_hash,line_count. Where the line count is the number of lines the
user has read so far. The advantage of storing files by content hash, is that if the file
is reopened from a different directory, or from a different file name, or even a different
machine, the user will be able to resume reading where he left off. That is, the information your script stores about the file depend only on the content of the file and not
its name/location.
Here are the contents of a sample .reader file:
3e3ac0b27b0adeb9138206eea2c43bb2,120
5eb63bbbe01eeed093cb22bb8f5acdc3,0
98f84fd484f8c2273f28cc645935f650,40
3. When the program launches, it will open the passed-in file name, compute its content
hash using the MD5 hashing algorithm, read the .reader_rc file, and skip the indicated
number of lines. Then it will display a page’s worth of lines (as dictated by the paging
argument) to the user.
4. When the user presses one of the command keys (n/p), the script will update the files
read lines count, rewrite .reader file to disk, and print a page to the terminal.
5. When the user presses q, the program quits.
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CS2043 Assignment 4 February 22, 2015
Summary/Notes:
− Python has many built-in hash libraries. Some are deprecated. Do not use the deprecated libraries. Python’s online documentation should guide you here. Another alternative is to call the Unix md5sum program through python.
− Your script should ideally capture the “command” key presses without the need to press
ENTER after each of them. However, it is accepted to require the user to press ENTER
before accepting a command key. So, pressing just ’n’ or ’n’ followed by ENTER are
both fine for advancing the page.
− Files beginning with a dot are hidden in Linux, so you won’t see them when you do an
ls. To see all files, do: ls -a
− Just to be clear, here is how you call the program:
∗ ./ereader.py the_republic.txt will launch the script with default paging of
40 lines per page.
∗ ./ereader.py -n 80 the_republic.txt will launch the script with paging set
to 80 lines per page.
− Since a user might use different paging even with the same file, make sure that the
.reader file contains number of lines displayed and not the number of pages displayed.
− To download public domain eBooks in plain text file format, check out the Gutenberg
project: http://www.gutenberg.org/browse/scores/top
Remember your best friends are the Python documentation: http://www.python.org/doc/,
the man tool and your favorite search engine.
If you need to ask questions, use the class discussion board on Piazza.
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