How do I check which shell I am using?

I read that terminal is nothing but shell, and Unix provides different flavors of shells:

• Bourne shell (sh)
• C shell (csh)
• TC shell (tcsh)
• Korn shell (ksh)
• Bourne Again shell (bash)

Questions:

• When I open a terminal window, which shell is opened by default?
• How do I check how many shells are installed?
• How do I change the shell used from my account?

You can type the following command in your terminal to see which shell you are using:

echo $0

The result will look something similar to the below if you are using the bash (Bourne Again Shell) terminal:

-bash

To find the shell you have on the default environment you can check the value of the SHELL environment variable:

echo $SHELL

To find the current shell instance, look for the process (shell) having the PID of the current shell instance.

To find the PID of the current instance of shell:

echo "$$"

Now to find the process having the PID:

ps -p <PID>

Putting it together:

ps -p "$$"

$SHELL gives you the default shell. $0 gives you the current shell.

For example: I have bash as my default shell, which I use for my Terminal App. But for my iTerm2 app, I use the command as the window opens: /bin/ksh.

So my $0 gives me /bin/ksh on iTerm2. $SHELL gives me /bin/bash on iTerm2. $0,$SHELL gives me /bin/bash on Terminal