Everything that happens at the command line: the shells themselves, terminal emulators and multiplexers (tmux, screen, tmate, terminator), session recording (asciinema, scriptreplay), and the utilities that glue commands together (xargs, parallel, watch, history).

Shells¶

sh · bash · dash · ash · zsh · fish

Which shell am I in?¶

echo "$0"                              # current shell (prefixed with - for a login shell)
ps -p $$ -o comm=                      # same, more reliably
echo "$SHELL"                          # your *login* shell, not necessarily the one running now
getent passwd "$USER" | cut -d: -f7    # login shell from the passwd database
ls -l /bin/sh                          # what sh actually points to
cat /etc/shells                        # shells allowed as login shells

Change your login shell with chsh -s "$(command -v zsh)". The path must be listed in /etc/shells, and the change takes effect at your next login. Keep a root or sudo session open while testing a new login shell, in case its config breaks logins.

Choosing a shell¶

A reasonable default: write scripts for #!/bin/sh when they need to run anywhere (containers, other distros), or for #!/usr/bin/env bash otherwise, and use whichever interactive shell you like. The interactive shell and the scripting shell don't have to be the same.

Other shells¶

• ksh (KornShell): the ancestor of many bash features. ksh93 and the smaller mksh are still found on commercial Unix, OpenBSD (/bin/ksh is pdksh-derived), and Android.
• tcsh: the C shell family. Its syntax is unlike sh, it was historically the FreeBSD root shell, and it is a poor choice for scripting.
• Nushell, Elvish, and xonsh: newer shells that pass structured data (tables, records) through pipelines instead of text. Nushell is written in Rust.