Check result of write (thans to Alexander Kapshuk <alexander.kapshuk@gmail)

cat.c

@@ -9,8 +9,12 @@ cat(int fd)
 {
   int n;
 
-  while((n = read(fd, buf, sizeof(buf))) > 0)
-    write(1, buf, n);
+  while((n = read(fd, buf, sizeof(buf))) > 0) {
+    if (write(1, buf, n) != n) {
+      printf(1, "cat: write error\n");
+      exit();
+    }
+  }
   if(n < 0){
     printf(1, "cat: read error\n");
     exit();