letitbeat / unix-lab

Hands-on laboratory on Unix and shell scripting for the students of Introduction to Computer Science class.

Introduction to Unix & Shell Scripting Laboratory

In this laboratory you will practice some of the commands studied at class and gain experience writing shell scripts.

Prepared by: Jorge López <jorge.lopez [at] telecom-sudparis.eu> and José Reyes <jose.reyes [at] telecom-sudparis.eu>

Part 1 - Unix Commands

1. Create a directory named Lab1, all exercises will be done in this directory

2. Create a file with the file names in the directory /usr/lib64 and append to that file the number of files in that directory, name the file 1.txt

3. Create a file containing the command used to recursively display all the files inside the /usr/ directory that are directories, name the file 2.cmd

4. Create a file named 3.cmd containing the command used to recursively display only the name and the modification dates (and times) of the files inside the /usr/ directory that have the word "power" in the name and that are directories

5. Create a file named 1.cmd and write the command to create a file called allusrlib64laandsh.txt with the content of all the files in the directory /usr/lib64 with the extensions .la and .sh

6. Give only execute rights to the user, none to the group nor to others on the file 1.cmd; execute the command 1.cmd, and capture its output on 1.out, append the command used to execute the file and the output of ls -l (to 1.out)

7. Create a file named 4.cmd with the command for listing all environment variables that in their content have a colon (:), just the variable names (hint: you can replace for the empty string to delete certain part)

8. Download the file http://www.tcpdump.org/release/tcpdump-4.9.2.tar.gz, decompress it and display all the lines inside all the files of tcpdump that match "0x20"; create a file with the command used to do this, name it 5.cmd (hint: find)

9. Create a file named 6.cmd with the command used display the current temperature in Paris (hint: wttr.in)

Part 2 - shell scripts

Task 1

Let's warm up our shell scripting skills!

For the first task we will be implementing a basic arithmetic calculator, our calculator should accept 2 arguments from the standard input and compute the addition, difference, multiplication and division of the provided arguments.

Example of the expected output:

$ ./calculator.sh 20 3
sum 20 + 3 =  23
diff 20 - 3 =  17
mult 20 * 3 =  60
div 20 / 3 =  6

In case the user executes the script without any arguments, it should prompt the user a message to enter them.

Example:

$ ./calculator.sh
Please enter operand a:
3
Please enter operand b:
10

sum 3 + 10 =  13
diff 3 - 10 =  -7
mult 3 * 10 =  30
div 3 / 10 =  0

If you notice something interesting in the results for div is the fact that bash expression only uses integers, if you like to extend the functionality to allow other than integers, then an external tool like bc is necessary

Hints: variables, arithmetic, if statements, read

Task 2

How much free RAM memory do I have in my system? Is there enough to install and run applications?

In Linux systems you can use free to get a report on system's memory usage.

The output without using any option, should be something similar to this:

$ free
            total     used    free     shared   buffers  cached
Mem:          595      482     112         0       63     324

-/+ buffers/cache:      93     501
swap:                   0        0       0

Our goal on this task is to implement a light version of free! Which when executed will show information of total, used and free RAM in MB.

Example:

$ ./free.sh
total	free	used
3947 MB	1809 MB	2137 MB

In Unix-like systems proc filesystem is a pseudo-filesystem which provides an interface to kernel data structures and system information, you can see information about memory utilization by executing cat /proc/meminfo

Hint: cat, grep, awk

Bonus: extend your script to accept an argument n and based on that the script should print the information n number of times every second

Example:

$ ./free.sh 3
total	free	used
3947 MB	1809 MB	2137 MB
total	free	used
3940 MB	1802 MB	2145 MB
total	free	used
3937 MB	1899 MB	2147 MB

Task 3

For the last task of this laboratory, we will fetching and manipulating data! Fetching/accessing data from the web is a very common task nowdays and Unix-like systems provide us with very handy tools to do so.

The first step to complete this task is to fetch the data in CSV format from the following url: https://bit.ly/2ATet9V and store it in the current directory.

Once we have the file which contains information of users in the following structure: id, fist_name, last_name, email our task is to list the data in the following format fist_name last_name, email but obfuscating the email so we don't show sensitive information of the users in the console!

Example of execution:

$ ./data-processor.sh

Leo Scoles, lscolesg@****.***
Emmanuel Staff, estaffa@****.***
Suzann Terne, sternen@****.***
...
...

Hints: curl -L, sed

Enjoy!

Final task

Create a file containing all the files created inside Lab1 including the scripts, append your name; zip it and email it to us: jorge.lopez [at] telecom-sudparis.eu, jose.reyes [at] telecom-sudparis.eu