The shell.
echo $SHELL
exit.
read (shell builtin command)
Strictly speaking, a "shell" is simply the interface between the user and the rest of the operating system. In that definition not all shells on Linux are command lines. However, most day-to-day usage of the term "shell" does refer to command line user interfaces. Finally, "Linux shell" is not a thing. Linux is an operating system, specifically a kernel, not a shell. Most Linux distributions use BASH, but I personally prefer ZSH.
You get a command not found. Linux is case sensitive. So, for example: The command "systemctl" will not be the same as "SystemCTL" to a shell in Linux. One will work, the other will return an error saying there's no such command.
yeah yeah
That would be a semi-contradiction; the command line would need to be already running in order to enter a command. The name of the program that actually provides the command line is called a shell. There are many different shells available for Linux, including Bash, ash, C Shell, fish, ksh, zsh, and scsh.The default command shell is /bin/sh (not /bin/bash, note).
The very first one, period. The first shell for Unix didn't originally have a name but has since been referred to as the Thompson shell. The first shell ported to Linux was bash.
It is not a command. It is an option for a command. Depending on the command it can modify the actions taken.For cp, mv and rm it makes the command interactive (are you sure). For ls it shows the inodes of files.
k is not a standard command in Linux.
Type exit to leave a terminal.