Bash, Zsh, sh, tcsh, and the TUI tools built on top of them - prompts, scripting, multiplexers, and terminal troubleshooting.
Microsoft's August 2016 announcement put PowerShell on GitHub and introduced it on Linux and macOS, changing its scope well beyond Windows administration.
tmux 3.0 shipped in late 2019 with changes from its normal development process - the major version bump was not a promise of semantic-versioning upheaval.
Interactive Bash editing is a library-driven state machine: keymaps, completion hooks, history, and terminal escapes all meet inside GNU Readline.
Reliable shell cleanup requires understanding signals, traps, process groups, and the important difference between a normal exit and an uncatchable termination.
PTYs and a persistent server process explain how tmux and screen survive a dropped SSH connection, not just several shells in one window.
After accidentally catting a binary file, the terminal shows strange characters or wrong colors - the shell is fine, the terminal's display state is what broke.
Commands seem to vanish between sessions, or history from multiple terminals overwrites instead of combining - how history writing works and the fix for each.
Opening a new terminal tab shouldn't take a visibly annoying second or two - how to find which specific config line is responsible, rather than guessing.
Wrong or missing colors specifically inside Windows Terminal connected to WSL, even though the same shell config looks fine over plain SSH.
Every shell in daily use today descends from a 1971 command interpreter, branching through PWB, Bourne, and C shell into the families still visible now.