System Commands OPPE 1: January 2026 (January 2026 term)

Given a list of filenames (with extensions), one per line, count the number of files for each extension. Output format: count .ext, sorted by descending count, then by descending extension for ties.

Instructions

• Write your script in script.sh.
• Read from standard input, write to standard output.
• Extensions are case-insensitive; output in lowercase.
• Count column is right-aligned to 2 characters.

Sample Input

hello.txt
bye.pdf
cats.txt
video.mp4
music.mp3
document.docx
list.txt
song.mp3
movie.MP4

Sample Output

 3 .txt
 2 .mp4
 2 .mp3
 1 .pdf
 1 .docx

Constraints

• Filenames always contain an extension.
• Extensions may be in any case; output must be lowercase.
• Output must be in lowercase.

Given n, find all twin-prime pairs whose sum is <= n. Print each pair as (p1, p2), sorted ascending by the first prime.

Instructions

• Write your script in script.sh.
• Read n from standard input.

Sample Input

24

Sample Output

(3, 5)
(5, 7)
(11, 13)

Constraints

• n is a positive integer <= 10000.

Given a string, check if its SHA-1 hash contains the string. If not, hash the hash and check again. Repeat up to 10 times. Print the iteration number and hash for each step. Stop when found; print Not Found after 10 iterations if never found.

If the input contains non-hex characters, immediately print Not Found (it can never appear in a SHA-1 hash).

Instructions

• Write your script in script.sh.
• Read one line from standard input.
• Check is case-insensitive.

Sample Input 1

g

Sample Output 1

Not Found

Sample Input 2

12

Sample Output 2

1: ad552e6dc057d1d825bf49df79d6b98eba846ebe
2: ab16bf05b01c833603826780711e0012597f02d7

Constraints

• Input contains only printable alphanumeric characters.