bash / zsh / fish

# ===== Which shell am I in? =====
echo $0          # current shell name
echo $SHELL      # default login shell
ps -p $$         # parent process: the shell binary

# ===== Common shells =====
# bash    GNU Bourne-Again Shell; default on most Linux distros
# zsh     Z shell; default on macOS since Catalina; rich completion + themes
# fish    Friendly Interactive Shell; sane defaults; not POSIX-compatible
# dash    Debian Almquist; small, POSIX, fast; symlinked as /bin/sh on Debian
# ash     BusyBox shell; used in Alpine containers
# ksh     KornShell; ancestor of bash + zsh; rare today

# ===== Where the config lives =====
# bash:   ~/.bashrc (interactive), ~/.bash_profile / ~/.profile (login)
# zsh:    ~/.zshrc (interactive), ~/.zprofile (login)
# fish:   ~/.config/fish/config.fish

# ===== Change your default shell =====
chsh -s /bin/zsh
# Log out + back in.

# Inside a script:
#!/usr/bin/env bash
# or #!/bin/sh for portable POSIX scripts

# ===== Essentials any shell gives you =====
# - Variables: NAME='Alex'  -> echo $NAME
# - Pipes: cmd1 | cmd2
# - Redirection: > >> < 2> 2>&1
# - Background: cmd &
# - Job control: fg, bg, jobs, kill %1
# - History: ! prefix, Ctrl+R reverse search
# - Tab completion (richer in zsh + fish)

# ===== Frameworks + themes =====
# zsh:    oh-my-zsh, prezto, starship prompt
# bash:   bash-it, starship
# fish:   built-in goodies, oh-my-fish

# ===== Starship (cross-shell prompt) =====
curl -sS https://starship.rs/install.sh | sh
# Add to ~/.zshrc:
eval "$(starship init zsh)"

# ===== POSIX vs feature-rich =====
# Production scripts: target POSIX sh; portable across distros + Alpine containers
# Interactive use: pick your favourite (zsh or fish for features; bash for ubiquity)

# ===== Patterns to internalise =====
# - One shell per machine for interactive use; scripts target POSIX where possible
# - shellcheck for every script
# - History settings: HISTFILE, HISTSIZE, ignoring duplicates
# - set -euo pipefail at the top of scripts that should fail loudly

# ===== Pitfalls =====
# - #!/bin/sh assuming bash features (arrays, [[ ]]) -> breaks on Alpine
# - chsh to fish for scripting use; many tools assume bash on stdin
# - Letting your dotfiles drift across machines; use a chezmoi / yadm setup
# - Sourcing untrusted scripts in your rc file

# bash is the default on most servers.
# zsh is the default on modern macOS.
# fish is friendly but not POSIX.
echo $0