Lab #2 | NSWI177

Information below is not for the current semester. The current semester can be found here.

Other labs: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12.

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Lab #2 (Feb 24 – Feb 28)

Before class

What is a terminal, which terminal emulators are there (hint: konsole, xterm, …)?
What is stdout, stdin and stderr?
What is a pipe (in the process chaining sense)?
What is a manpage?
What is a shell?
What are filename wildcards?
Which directory is aliased to tilda (~)?
Write a program in Python (or in other reasonable language) that copies its stdin to its stdout and stderr.
Write a program in Python that takes as command-line argument (sys.argv) one natural number and prints a random number in the range of 0 to the provided number. On bad usage (no number, invalid number etc.) it shall print Bad usage.

Topic

Introduction to command-line environment of GNU/Linux.
Working with files in command-line.
Effective command-line usage.
Basic utilities.

Exercises

Write a program in Python (or in other reasonable language) that copies its stdin to its stdout and stderr. Solution.

Write a program in Python that takes as command-line argument (sys.argv) one natural number and prints a random number in the range of 0 to the provided number. On bad usage (no number, invalid number etc.) it shall print Bad usage. Solution.

Choose one terminal based text editor and familiarize yourself with it.

List the content of your home directory. Then repeat for hidden files. Solution.

Print the detailed (long) listing of the /etc directory. Solution.

Create directories b and b/c using a single command. Solution.

Create a file file with space.txt. How is it treated by the ls command? What does a tab completion do with this file? Solution.

Create a directory a and inside of it create a text file --help containing Lorem Ipsum. Print the content of this file and then delete it. Solution.

Create a directory called a and inside of it create files called alpha.txt and *. Then delete the file called * and watch out what happened to the file alpha.txt. Solution.

10.

Create files a.txt, b.txt and .hidden.txt. Then list all files with extension txt. Solution.

11.

Print the content of the file /etc/shells. Solution.

12.

Print the content of the file /etc/passwd sorted by the rows. Solution.

13.

Print the first and fifth column of the file /etc/passwd. Solution.

14.

Count the lines of the file /etc/services. Solution.

15.

Print the first three lines of the file /etc/passwd. Solution.

16.

Print last two lines of the files /etc/passwd and /etc/group using a single command. Solution.

#!/usr/bin/env python3

import sys

def main():
    for line in sys.stdin:
        line = line.rstrip('\n')
        print(line)
        print(line, file=sys.stderr)

if __name__ == '__main__':
    main()

#!/usr/bin/env python3

import random
import sys

def terminate():
    print("Bad usage", file=sys.stderr)
    sys.exit(1)

def main():
    if len(sys.argv) != 2:
        terminate()
    try:
        top = int(sys.argv[1])
        if top <= 0:
            raise ValueError("Bad range")
    except ValueError:
        terminate()
    print(random.randint(0, top))

if __name__ == '__main__':
    main()