Example

       #include <unistd.h>
       #include <stdlib.h>
       #include <stdio.h>
       #include <fcntl.h>

       main()
       {
           int fd,
               i;
           char buf[10];
           FILE *fp ;          /* Temporary STDIO file */

           /* Create a dummy data file  */

           if ((fp = fopen("test.txt", "w+")) == NULL) {
               perror("open");
               exit(1);
           }
           fputs("XYZ\n",fp) ;
           fclose(fp) ;

           /* And now practice "read" */

           if ((fd = open("test.txt", O_RDWR, 0, "shr=upd")) <= 0) {
               perror("open");
               exit(0);
           }

           /* Read 2 characters into buf.  */

           if ((i = read(fd, buf, 2)) < 0) {
               perror("read");
               exit(0);
           }

           /* Print out what was read.  */

           if (i > 0)
               printf("buf='%c%c'\n", buf[0], buf[1]);

           close(fd);
       }