How to know the current shell you are logged in?

If you are using Linux or Unix Terminal and are not able to determine which shell are you currently active in, you can determine it by simply echoing $0 on the current prompt.

b2391b608026# echo $0

zsh

root@b2391b608026:/# echo $0

bash

root@b2391b6026:/# echo $0

rbash

# echo $0

dash

# echo $0

sh

If you want to know the list of shells available on your Operating System, just cat /etc/shells

# /etc/shells: valid login shells
/bin/sh
/bin/bash
/usr/bin/bash
/bin/rbash
/usr/bin/rbash
/bin/dash
/usr/bin/dash
/bin/zsh
/usr/bin/zsh