Master Linux Permissions and Python Regex: Key Interview Questions Explained

Question 1 – Linux Permissions

How to modify file and directory permissions in Linux?

Use chown [-R] new_owner file to change the owner, chgrp [-R] new_group file to change the group, and chmod [-R] mode file to set permissions. Modes can be expressed symbolically (e.g., rw-r--r--) or numerically (e.g., 644). The -R flag applies changes recursively.

Linux stores permissions in a 16‑bit field; special attributes can be listed with lsattr and set with chattr. Windows uses ACLs, while Unix focuses on permission bits.

Question 2 – Python regex

What is the difference between match() and search() in the re module? re.match(pattern, string[, flags]) checks only at the beginning of string. re.search(pattern, string[, flags]) scans the entire string for the first occurrence.

Examples:

print(re.match('super', 'superstition').span())  # (0, 5)
print(re.match('super', 'insuperable'))          # None
print(re.search('super', 'superstition').span()) # (0, 5)
print(re.search('super', 'insuperable').span()) # (2, 7)

Readers are encouraged to think about the answers before reviewing them.