Unix

How the shell finds commands.

What runs, how it's controlled, and how to stop it.

Who can read, write, or execute — and why it matters.

Inodes, hard links, symlinks, and where config lives.

stdin, stdout, stderr — and the essential JSON knife.

awk vs sed vs grep — picking the right tool for the line.

Walk the live filesystem or query an index — and how to feed xargs safely.

set -euo pipefail, trap, subshells — and when to graduate to Python.

apt, dnf, brew, pacman, nix — and why Nix solved 'works on my machine'.