Operating systems, infrastructure, emulation, and technical history.
A tool you just installed is definitely on disk, but the shell insists it doesn't exist - almost always a PATH problem, with only a few actual explanations.
TUI apps render clipped over SSH, or the terminal doesn't rewrap after resizing - the remote shell has a stale idea of the terminal's actual dimensions.
A shortcut that works outside tmux does something different, or nothing, inside a session - how the prefix key and keybinding layers interact.
Re-running the last command with sudo and fuzzy-searching everything typed today both rely on the same persisted, indexed log the shell writes to disk.
The actual difference between an alias and a function, when each is the right tool, and how to avoid the mistakes that make aliases behave unpredictably.
Setting up a terminal-based git interface for staging, committing, browsing history, and resolving conflicts visually without leaving the terminal.
Disclosed September 24, 2014, Shellshock let attackers run arbitrary commands via a Bash environment-variable flaw, with botnets scanning for targets within hours.
Pressing Tab and getting a sensible list looks simple. Underneath, Bash and Zsh implement a programmable system matching rules specific to each command.
FreeBSD default shells did not evolve from the Bourne lineage behind Bash and Zsh - tcsh descends from a separate design built to feel more like C.
Trace ARPANET from NCP through TCP/IP, gateways and the 1983 transition-and correct the myth that one protocol simply swallowed every rival network.