1 jelson 1.1 /*
 2             * nbcat: a simple program similar to 'cat', but which uses
 3             * nonblocking reads.
 4             *
 5             * This utility can be used to copy the current contents of an emlog
 6             * device without blocking to wait for more input.  For example:
 7             *
 8             *        nbcat /var/log/emlog-device-instance > /tmp/saved-log-file
 9             *
10             * ...will copy the current contents of the named emlog device to a
11             * file in /tmp.
12             *
13             * This code is freeware and may be distributed without restriction.
14             *
15             * Jeremy Elson <jelson@circlemud.org>
16             * August 11, 2001
17             */
18            
19            #include <stdio.h>
20            #include <stdlib.h>
21            #include <unistd.h>
22 jelson 1.1 #include <fcntl.h>
23            #include <errno.h>
24            
25            int main(int argc, char *argv[])
26            {
27              int fd, retval;
28              char buf[4096];
29            
30              if (argc != 2) {
31                fprintf(stderr, "usage: %s <filename>\n", argv[0]);
32                exit(1);
33              }
34            
35              if ((fd = open(argv[1], O_RDONLY | O_NONBLOCK)) < 0) {
36                perror(argv[1]);
37                exit(1);
38              }
39            
40              while ((retval = read(fd, buf, sizeof(buf))) > 0) {
41                if (write(STDOUT_FILENO, buf, retval) < 0) {
42                  perror("writing to stdout");
43 jelson 1.1       break;
44                }
45              }
46            
47              if (retval < 0 && errno != EAGAIN) {
48                perror(argv[1]);
49                exit(1);
50              }
51            
52              return 0;
53            }