How do I find out what shell I am using on Linux/Unix?

last updated in Categories CentOS, Debian Linux, FreeBSD, Gentoo Linux, Howto, Linux, Shell scripting, Sys admin, Ubuntu Linux, UNIX

Both Linux and Unix provides various shell out of the box. One can find bash (Bourne Again shell), ksh (Korn shell), csh (C shell)/tcsh (TC shell), sh (Bourne shell) and more installed by default. However, how do you check which shell am I using? What is the best way to find out what shell I am using on Linux? The echo $SHELL is not so reliable. This page explains how to find out which shell I am using at a Linux, MacOS, FreeBSD, or Unix-like systems.