Scan Input, build lexical tokens

shell.c

// keep getline in a loop in case interruption occurs
int again = 1;
while (again) {
	again = 0;
	printf("%s", getprompt());
	linebuffer = NULL;
	len = 0;
	ssize_t nread = getline(&linebuffer, &len, stdin);
	if (nread <= 0 && errno == EINTR) {
		again = 1;        	// signal interruption, read again
		clearerr(stdin);	// clear the error
	}
}

// user pressed ctrl-D
if (feof(stdin)) {
	exit(0);
	return 0;
}

// lexically analyze and build a list of tokens
lexer_build(linebuffer, len, &lexerbuf);