UNIX for Advanced & Expert Users

I have a silly question here.

Under the shell prompt, when I launch a command (if the command is not part of shell, like 'awk') , how does the shell work?

I don't understand that if the command is not part of or supported by the shell, how does the shell action on this occassion?

Got this from google search... hope it help to understand...

A Unix shell, also called "the command line", provides the traditional user interface for the Unix operating system and for Unix-like systems. Users direct the operation of the computer by entering command input as text for a shell to execute.

Hi.

Text and references at Command line interface - Wikipedia, the free encyclopedia ... cheers, drl

The shell has:
- a Interpretive Programming Language
- Environment settings
- Variable assignment and substitution capabilities
can
- execute / substitute commands
- use pipeline
- redirect I/O
etc...

>I don't understand that if the command is not part of or supported by the shell, how does the shell action on this occassion?
For awk isnt an internal command the shell will search an executable called awk since that is what you entered at the STD input (the keyboard) using a search path you have in your env: the variable PATH, the first one found will be executed...
If the program could not be found, the shell will say so at your STD output (most certainly the display unit above the keyboard)
Simple no?

The shell forks, execs and waits for an external command such as awk to complete.

Do a Web seach "simple command line shell" and you will find plenty of examples of simple command line shells online. It is a standard homework assignment for many computer science courses.