even: skip every other byte in file/stdin

even.c

/* even, by Lionello Lunesu, placed in the public domain */
#include <stdio.h>

int even(FILE * f)
{
  char buf[4096];
  int r, read, wrote;
  while (1)
  {
    read = fread(buf, 1, sizeof(buf), f);
    for (r=1; r<read/2; ++r)
      buf[r] = buf[r*2];
    wrote = fwrite(buf, read/2, 1, stdout);
    if (wrote != 1)
      return 1;
    if (read != sizeof(buf))
      break;
  }
  return 0;
}

int main(int argc, char** argv)
{
  int i, r = 0;
  if (argc == 1 || (argc == 2 && argv[1][0] == '-' && !argv[1][1]))
    return even(stdin);
  for (i=1; i<argc; ++i)
  {
    FILE * f = fopen(argv[i], "r");
    if (f)
    {
      r = even(f);
      fclose(f);
      if (r)
        break;
    }
    else
    {
      r = 2;
    }
  }
  return r;
}