add-shell

Add a shell to /etc/shells

$ sudo add-shell [/usr/local/bin/zsh]

$ sudo add-shell [/bin/fish] [/bin/zsh]

add-shell shell [shell...]

add-shell is a Debian utility that safely adds new shell paths to /etc/shells. The /etc/shells file lists valid login shells that users can select with chsh.
The tool checks for duplicates and validates the path before adding it, making it safer than manually editing /etc/shells.

shell

Absolute path to the shell executable to add

Requires root privileges. The shell executable must exist and be valid. Not available on all distributions; on systems without this command, manually edit /etc/shells.

add-shell is part of the Debian packaging utilities, created to provide safe manipulation of /etc/shells during package installation scripts.

remove-shell(8), chsh(1), shells(5)