Shell

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A shell is a command-line interpreter that offers a text-based interface to users. It can be used as a command-line interface in a virtual console (or in a terminal emulator, over a serial connection, etc.), as a remote shell (over SSH, for example), or as a script interpreter (running prewritten commands).

Typically, the shell is the first program started after a user logs in at a terminal. The /etc/passwd file contains information defining the login shell for each user on the system. After login, a user can launch other shells from a terminal, change their login shell, or specify a shell to use under certain terminal emulators.

In Gentoo, the /bin/sh file is a symlink to the default system shell, and as such can link to one of several different POSIX shells. After following the Handbook, the default shell will be bash.

See the terminal emulator article for some general usage pointers.

Note
When writing scripts, care should be taken to reference the correct interpreter on the first line, with a shebang. A script beginning with #!/bin/sh should only use POSIX constructs and no bash specific code, for example.

Available software

Name Package Homepage Description
bash app-shells/bash https://tiswww.case.edu/php/chet/bash/bashtop.html The Bourne Again Shell, is the default shell on Gentoo. It is used by Portage, Gentoo's default package manager.
dash app-shells/dash http://gondor.apana.org.au/~herbert/dash/ The Debian Almquist Shell, a small, fast, and posix-compliant shell suited for startup scripts (as /bin/sh replacement).
fish app-shells/fish https://fishshell.com/ The Friendly Interactive SHell.
ksh app-shells/ksh http://www.kornshell.com/ The Original Korn Shell, 1993 revision (ksh93).
mksh app-shells/mksh https://www.mirbsd.org/mksh.htm An actively developed free implementation of the Korn Shell, and well suited for scripting.
tcsh app-shells/tcsh http://www.tcsh.org/ an enhanced version of the Berkeley C Shell (csh).
xonsh dev-python/xonsh http://xon.sh/ A Python-based shell that falls back to bash commands.
yash app-shells/yash https://yash.osdn.jp/ Yet Another SHell, is a POSIX-compliant command line shell written in C99 (ISO/IEC 9899:1999).
zsh app-shells/zsh http://www.zsh.org/ An advanced shell that is the chosen interactive shell for many users.

For more shell options, see the output of the following command (eix required):

user $eix -cC app-shells

Configuration

Changing the default system shell

Important
Changing /bin/sh to something other than bash can cause rare issues with badly written scripts, e.g. scripts starting with #!/bin/sh but using bash specific code. bug #526268

System administrators can change the default system shell using the eselect utility. This utility changes the system shell by replacing /bin/sh with a symlink to a different POSIX compatible shell.

If it is not already installed, emerge the app-eselect/eselect-sh package:

root #emerge --ask app-eselect/eselect-sh

To list possible shell options use:

root #eselect sh list

To set, for example, dash as the default system shell:

root #eselect sh set dash

Changing a user's shell

Important
Some shells, such as fish, can cause issues if directly set as the login shell. See the fish#Caveats article for workarounds.

A user's default shell (aka login shell) can be changed on an individual basis using the chsh command. To change the login shell for the current user, type chsh and enter a correct path to the new shell. In the example below, a user named Larry the cow (Larry) is changing his login shell from /bin/bash to /bin/zsh:

user $chsh
Changing the login shell for larry
Enter the new value, or press ENTER for the default
	Login Shell [/bin/bash]: /bin/zsh

chsh can be used by the super user account to change the login shell for any user.

Troubleshooting

Garbled display

The output of a shell can, in some conditions, become corrupt. See the terminal emulator article for instructions to help fix this.

See also