shell: use re-allocated buffer to store additional characters

source/shell/cmd.c

@@ -11,7 +11,7 @@ struct cmd main_cmds[] = {
 
 static char *prompt(const char *prefix)
 {
-	char *alloc, *line, *s;
+	char *alloc, *line;
 	size_t nbytes = 0, nalloc_bytes = 16;
 	char c;
 
@@ -20,8 +20,6 @@ static char *prompt(const char *prefix)
 	if (!(line = malloc(nalloc_bytes)))
 		return NULL;
 
-	s = line;
-
 	while ((c = getchar()) && c != '\n') {
 		putchar(c);
 
@@ -34,12 +32,11 @@ static char *prompt(const char *prefix)
 			line = alloc;
 		}
 
-		*s++ = c;
-		nbytes++;
+		line[nbytes++] = c;
 	}
 
 	printf("\n");
-	*s = '\0';
+	line[nbytes] = '\0';
 
 	return line;