System Commands OPPE 1: May 2025 (May 2025 term)

Motivation

We can iterate over each line from standard input by using while and read commands.

while read -r line; do
    # Process each line here
done

Problem Statement

Given /etc/passwd file as standard input (&0), extract the usernames and convert them to lowercase.

Instructions

• Write your solution in script.sh shell script file.
• The script should read the input from standard input (&0).
• The output should be printed to standard output (&1).
• No files will be provided, so you need to read from standard input.

Sample Input

root:x:0:0:root:/root:/bin/bash
user:x:1000:1000:User:/home/user:/bin/bash
Sayan:x:1001:1001:Sayan:/home/sayan:/bin/bash

Sample Output

root
user
sayan

Constraints

• The input will always be in the format of /etc/passwd.
• Usernames are the first field in each line, separated by a colon (:).

Hints

• Try using variable manipulation solely to solve this question.

Motivation

Folding

A line of text can be folded into multiple lines in two broad ways:

• Fixed-width folding: where each line has a fixed number of characters. This can be done using the fold command in Linux.
• Variable-width folding: where the line is folded based on the content, such as breaking at spaces or punctuation. This can be done using the grep -o command in Linux.

> cat data
123456789
> fold -w 3 data
123
456
789

> grep -o '[0-9]\+' <<< "1,23,456"
1
23
456

Unfolding

Unfolding is the reverse of folding, where multiple lines are combined into a single line. This can be done using the paste command in Linux.

> cat data
1
2
3
> paste -sd'*' < data
1*2*3

Read more about them in man fold, man grep, and man paste.

Problem Statement

You are given a $n$ dimensional vector in one line. Find the L1 norm of the vector, which is the sum of the absolute values of its components.

Instructions

• Write your solution in script.sh shell script file.
• The script should read the input from standard input (&0).
• The output should be printed to standard output (&1).

Sample Input

[1,-25,4]

Sample Output

30

Constraints

• The expressions will always be well-formed.
• The vector can have any number of elements.
• The components of the vector can be positive or negative integers.

Motivation

Fibonacci Numbers

Fibonacci numbers are a sequence of numbers where each number is the sum of the two preceding ones, usually starting with 1 and 1. The sequence commonly starts as follows: 1, 1, 2, 3, 5, 8, 13, 21, and so on.

$$F_n = F_{n-1} + F_{n-2}$$

Problem Statement

You are given a positive integer n. Your task is to print a triangle of n rows consisting of the first $n \times (n + 1) / 2$ fibonacci numbers.

Instructions

• Write your solution in script.sh shell script file.
• The script should read the integer n from standard input.
• The output should be formatted as a triangle, with each row containing the appropriate number of fibonacci numbers.

Sample Input

4

Sample Output

1
1 2
3 5 8
13 21 34 55

Constraints

• n is a positive integer.
• The output should be formatted with each number separated by a space.
• The last number in each row should not have a trailing space.