Question

In how many categories, commands of UNIX operating system classified?

(a) 1

(b) 2

(c) Many

(d) 0

This question was addressed to me in an online quiz.

The question is from Commands in chapter The Unix Architecture & General Purpose Utilities of Unix

Answer 1

Correct answer is (b) 2

Easiest explanation: There are two broad categories in which the classification of commands is based on UNIX. They are namely—external commands and internal commands. External commands are those commands that have an independent existence in the /bin directory i.e. these are the executables which are present in separate files while Internal commands are built-in commands which are built into the shell. Example, ‘ls’ is an external command while ‘echo’ is an internal command.