A great variety of shells is available for Unix, including Bourne-compatible shells (sh, bash, ksh, pdksh, ash, dash, etc.), C shell (csh, tcsh), Z shell (zsh), and the Friendly Interactive Shell (fish).
The default interactive shell in many Linux distributions is Bourne-Again Shell (bash). The default script-execution shell in some Linux distribution is Debian Almquist shell (dash). The default shell in macOS used to be Bash as well but is now Z shell (zsh).
All Unix shells are similar, but they have different features. If you are beginning, and you are not aware of the differences between shells, then you probably want to start with a Bourne-compatible, POSIX (Portable Operating System Interface)-compatible shell such asbash orksh.
Bourne-compatible shells:
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BSD introduced the C shell, which sometimes resembles slightly the C programming language. This shell iscsh. The shelltcsh is csh with more features. These shells are NOT Bourne-compatible. Many of the features were later added to the Bourne-compatible shells (except old copies of sh). When these features work differently in C shell and Bourne-compatible shells, this guide will describe the Bourne-compatible shells.
If csh or tcsh is your default shell, you might benefit by using bash or ksh to get Bourne-compatibility and POSIX features. Some users still prefer the C shell.
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There are alternative shells such aszsh, the Z shell. The Z shell boasts extra and unusual features that make it the preferred shell of many (for example, it has a builtin ftp client). Though the Z shell is almost Bourne-compatible, it differs in enough ways that its default behaviour is not Bourne-compatible, though zsh is capable of masquerading as a Bourne shell when so instructed. It can also emulate ksh.
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If you do not like the shell that you are using, you might want to use a different shell such asksh orbash. Shells are normal programs, and can be run easily. The SHELL environment variable will still contain the default shell. Theexit command will return you to the first shell.
tcsh>echo $SHELL/bin/tcshtcsh>bashbash$echo $SHELL/bin/tcshbash$exitexittcsh>
Find list of shells by looking at/etc/shells (which can be done by executingmore /etc/shells). The commandpasswd -e, on some systemschsh, will prompt for a new shell. To change frombash totcsh one can simply executechsh which will query the user to enter the absolute path to a new shell:
$chshPassword: Changing the login shell for baldurEnter the new value, or press ENTER for the default Login Shell [/bin/bash]:/bin/tcsh
or the user can specify the shell:
$chsh -s /bin/tcshPassword:
The shell must be specified using its absolute path, which may be found usingwhich tcsh.
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