The first command shell was 'sh', the Bourne shell (Steven Bourne).
A shell program is called a command processor because it has to process commands according to what the user wishes to do. Along with executing commands as specified by the user it also has its own programming language and can be instructed to do things programmatically.
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.
In an interactive shell session the shell program waits for the user to type in a command. When receiving a command the shell program will then attempt to locate it and process (execute) the command. You are interacting with the shell. Running a shell file requires a pre-stored series of commands stored in a file. Unless the shell program you are running is interactive then the shell executes each command in sequence, without involving the user at all.
The filename for the command processor shell for most Windows versions from XP and up are command.com (usually used for older DOS applications that are designed to work with Windows) and cmd.exe. They both exist in \Windows\System32.
While the command is executing, the shell waits for the process to finish.
The output would be 'shell shell' (without the quotes, of course)
echo $SHELL
While the command is executing, the shell waits for the process to finish.
Typically the 'exit' command gets you out of the current shell environment you are in; if this is the login shell then you will be logged out of the system.
A shell script is used to automatically enter a series of commands without having to make the user type them out.
The echo command echoes out any of the command line arguments given to it. It is commonly used in shell scripts to echo what portions of the shell script are doing.
The shell.