Due: Wednesday, October 17, 2007 at NOON
Turnin link here
You will get experience writing bash scripts. You will experiment with the grep, sed, and awk utilities. You will learn about a program called gnuplot for plotting files.
Note: The instructions for this assignment may seem a bit long. This is because we try to give you plenty of sample outputs and hints for each question. We hope this will help you complete the assignment faster.
In addition to the lecture notes, you may find "The Linux Pocket Guide" a useful reference for completing this assignment (in particular, pages 166 and following).
Online manuals:
In general, whenever you need to use a new tool, you should get into the habit of looking for documentation online. There are usually good tutorials and examples that you can learn from. As you work on this assignment, if you find that you would like more information about a tool (awk, sed, grep, or gnuplot), try searching for the name of the tool or the name of the tool followed by keywords such as "tutorial" or "documentation".
Download the file: hw2.tar.gz.
(You can also access the above file at /cse/courses/cse303/07au/hw2.tar.gz on the instructional servers)
Extract all the files for this assignment using the following command:
> tar -zxvf hw2.tar.gz
You should now see a directory called hw2.
If you see it, you are ready to start the assignment. If this procedure did not work for you, please contact a TA or talk to another student in the class.
Because you did very well in CSE303, you were offered a summer position in a research group.
As part of your summer job, you would like to run the following experiment. Given a list of 100 popular websites, you would like to measure the sizes of their index pages (the first index.html file that the browser downloads when you visit the site). You suspect that popular sites must have very small index pages because they need to handle a heavy user load.
We provide you the list of popular websites in the file popular.html (this list comes from 100bestwebsites.org)
One approach would be to manually download each index page in the list, and use wc to compute its size in bytes. You could then manually put all the results in a table and plot some graphs to display the results. This approach would be long, tedious, and error prone. It would also be painful if you wanted to repeat the experiment on the 100 least popular websites. Instead, you decide to automate the experiment by writing a set of scripts.
In a file called perform-measurement.sh, write a bash script that takes a URL as argument and outputs the size of the corresponding page in bytes.
For example, executing your script with the URL of the class website as argument:
> ./perform-measurement.sh http://www.cs.washington.edu/education/courses/cse303/07au/hw0.html
should output only the number 1856:
> 1856
If the user does not provide any arguments, the script should print an error message and exit.
If the user provides an erroneous argument or downloading the requested page fails for any other reason, the script should simply print the number "0" (zero).
Hints:
The list of popular websites is in html format. To run an experiment automatically on each URL in this list, we need to extract the URLs and write them into a text file. There are several ways in which this can be done, and different utilities (awk, sed, grep) can help.
We would like you to use grep and sed.
In a file called parse.sh, write a script that extracts the URLs and writes them into a text file. The script should take two arguments: the name of the input html file and the name of the output file for the results.
For example, executing:
> parse.sh popular.html popular.txt
Should write the following content into popular.txt:
http://www.100bestwebsites.org/oledata.mo
http://www.yahoo.com/
http://www.google.com/
...
If the user provides fewer than 2 arguments, the script should print an error message and exit.
If the html file provided as argument does not exist, the script should print an error message and exit.
If the txt file provided as argument (for the output) exists, the script should simply overwrite it without any warning.
Q: How come popular.txt contains only 88 urls? Is it a bug in your script or a bug in the data? You don't need to answer this question in writing, just think about it for yourself.
Hints: step-by-step instructions
Note: the first line that will appear in the result file (http://www.100bestwebsites.org/oledata.mo) should technically not be there, but don't worry about it. Just leave it there or remove it manually.
To perform the experiment, your need to execute the script perform-measurement.sh on each URL inside the file popular.txt. Once again, you would like to do this automatically with a script.
In a file called run-experiment.sh, write a shell script that:
rank URL page-size
To debug your script, instead of trying it directly on popular.txt, we provide you with a smaller file: popular-small.txt. You should execute your script on popular-small.txt until it works. Only then try it on popular.txt.
Executing your script as follows:
> run-experiment.sh popular-small.txt results-small.txt
Should produce the following output:
Performing measurement on http://www.cs.washington.edu/education/courses/cse303/07au/
...success
Performing measurement on http://www.cs.washington.edu/education/courses/cse303/07au/course_glossary.html
...success
Performing measurement on http://i.will.return.an.error
...failed
Performing measurement on http://www.cs.washington.edu/education/courses/cse303/07au/textbooks.html
...success
And the content of results-small.txt should be similar to the ones below. Note that the exact value will change as we edit the class website!
1 http://www.cs.washington.edu/education/courses/cse303/07au/ 9877
2 http://www.cs.washington.edu/education/courses/cse303/07au/course_glossary.html 8608
4 http://www.cs.washington.edu/education/courses/cse303/07au/textbooks.html 2192
As another example, after executing your script as follows:
> run-experiment.sh popular.txt results.txt
The file result.txt, should contain results similar to the ones shown below (when you run your experiment, the exact values may differ)
2 http://www.yahoo.com/ 10047
3 http://www.google.com/ 3951
4 http://www.amazon.com/ 60700
...
It is hard to understand the results just by looking at a list of numbers, so you would like to produce a graph. More specifically, you would like to produce a scatterplot, where the x-axis will show the rank of a website and the y-axis will show the size of the index page.
Luckily, you talk about your problem to your friend Alice. She suggests that you use a program called gnuplot to produce the graph. Because she used it many times before, Alice helps you write the necessary gnuplot script called produce-scatterplot.gnuplot. Note that the gnuplot file expects your experimental results to be stored in a file called results.txt.
Produce the graph with the following command:
> gnuplot produce-scatterplot.gnuplot
The script should produce a file called scatterplot.eps. You can view it with gv:
> gv scatterplot.eps
Write your answers to the following questions in a file called problem4.txt:
Q1: Examine the gnuplot file produce-scatterplot.gnuplot. Ignoring the first line, explain what the rest of the script does.
Q2: Looking at the scatterplot, what can you conclude about the relationship between the popularity of a site and the size of its index.html file? Are these result what you expected?
Here is the list of files that you need to turn in:
Please turn in your files here. (no need to zip up your multiple files)