Illegal command

Illegal command is a esolang created by User:Qazwsxplm, inspired by 'xxx' is not recognized as an internal or external command, operable program or batch file. and it imitates a common DOSBox error when you attempt to execute a command that does not exist.

Commands

Any command will be valid and prints:

Illegal command: (command name).

Commands are separated by line feeds.

Interpreter

Python

[print("Illegal command: '{}'.".format(x)) for x in __import__('sys').stdin.read().split('\n')]

C

The program implements a REPL, and uses the insecure function gets to read the program.

#include<stdio.h>
char _[1000000];
int main()
{
	while(!feof(stdin))
	{
		printf("C:\\>");
		gets(_);
		printf("Illegal command: '%s'.\n",_);
	}
}

Batch

@echo off
:bad
set /p x=C:\^>
echo Illegal command: '%x%'.
echo.
goto bad