What is the flow in UNIX or UNIX like operating system for commands execution?

As soon as we press the enter key after the command, the below sequence will be followed.

1.  Check alias and then execute the command(shell-built-in or external command) accordingly
2.  Shell built-in command
3.  External command

Note 1: If command is executed with absolute path then external command or script will run. Else above sequence will be followed.

Note 2: If PATH value is empty, then shell will presume that the command is available in the current directory and hence it will try to run it from current directory.