How does computer know whether on instruction you typed is a program?

A computer determines whether an instruction is a program by analyzing the input against predefined syntax and semantics of programming languages. When a user types a command, the operating system or interpreter checks if the input matches known executable files or scripts, often relying on file extensions or specific keyWords. If the input corresponds to an existing program or script, the system executes it; otherwise, it may return an error indicating an unrecognized command. Additionally, command-line interpreters and shells can help differentiate between built-in commands and user-defined scripts.