work without libio

retval/Makefile

@@ -1,8 +1,2 @@
-retval: retval.o ../libio/libio.o
-	$(CC) -o retval ../libio/libio.o retval.o
-
-retval.o: retval.c ../libio/libio.h
-	$(CC) -c -I../libio -o retval.o retval.c
-
-../libio/libio.o: ../libio/libio.c ../libio/libio.h
-	$(MAKE) -C ../libio
+retval: retval.c
+	$(CC) -o retval retval.c

retval/retval.c

@@ -1,8 +1,7 @@
-#include <ctype.h> /* isdigit(3) */
+#include <errno.h> /* errno */
 #include <stdio.h> /* fprintf(3), stderr */
+#include <stdlib.h> /* strtol(3) */
 #include <sysexits.h> /* EX_USAGE */
-#include <unistd.h> /* write(2) */
-#include "libio.h" /* fdprint(3), parse_uint(3) */
 
 static char *program_name = "retval";
 
@@ -14,11 +13,10 @@ usage:		fprintf(stderr, "Usage: %s [status]\n", argv[0] == NULL ? program_name :
 		return EX_USAGE;
 	}
 
-	for(s = 0; argv[1][s] != '\0'; ++s)
-		if(!isdigit(argv[1][s]))
-			goto usage;
-
-	s = parse_uint(argv[1]);
+	errno = 0;
+	s = strtol(argv[1], &argv[1], 10);
+	if(*argv[1] != '\0' || errno != 0)
+		goto usage;
 
 	return s;
 }