shred.c

   1 #include <fcntl.h>
   2 #include <unistd.h>
   3 #include <stdio.h>
   4 #include <sys/stat.h>
   5
   6 static int urandfd;
   7
   8 static off_t getfs(int fd) {
   9         struct stat st;
  10         if (fstat(fd, &st) != -1)
  11                 return st.st_size;
  12         return (off_t)-1;
  13 }
  14
  15 static int shred(char *fn) {
  16         int fd, ret = 1;
  17         off_t fs, curr = 0;
  18         unsigned char buf[16384];
  19         if((fd = open(fn, O_RDWR)) == -1) {
  20                 perror(fn);
  21                 return 1;
  22         }
  23         if((fs = getfs(fd)) == (off_t)-1) {
  24                 fputs(fn, stderr);
  25                 perror(": failed to get filesize");
  26                 goto out;
  27         }
  28         ret = 0;
  29         while(curr < fs) {
  30                 off_t left = fs - curr;
  31                 if(left > 16384) left = 16384;
  32                 read(urandfd, buf, left);
  33                 if(left != write(fd, buf, left)) ret = 1;
  34                 curr += left;
  35         }
  36 out:
  37         close(fd);
  38         return ret;
  39 }
  40
  41
  42 static int usage() {
  43         fputs(
  44                 "shred FILE1 [FILE2...]\n\n"
  45                 "overwrites contents of FILEs with random garbage\n"
  46                 , stderr
  47         );
  48         return 1;
  49 }
  50
  51 int main(int argc, char **argv) {
  52         if(argc < 2) return usage();
  53         if((urandfd = open("/dev/urandom", O_RDONLY)) == -1) {
  54                 perror("failed to open /dev/urandom");
  55                 return 1;
  56         }
  57         int i, f = 0;
  58         for(i=1; i<argc; ++i) {
  59                 f += shred(argv[i]);
  60         }
  61         close(urandfd);
  62         return f;
  63 }