#include <stdio.h>
#include <time.h>

/* Read input from standard input and write to both standard output
 * and a file. 
 * Supports only text files, and only short lines
 * -a       append to file
 * -t       prepend a timestamp
 */
void usage()
{
    fprintf(stderr,"Usage: some_command | tee [-a] [-t] outfile\n");
    exit (1);
}
int main(int argc, char *argv[])
{
  int		a;
  FILE          *fd = NULL;
  char		*mode = "w";
  char          buf[1000];
  char          *timestamper = NULL;
  char          tbuf[20];
  struct tm     *tm_p = NULL;
  time_t        time_p = 0;

  if (argc <= 1) {
    usage();
  }
  for (a = 1; (a < argc) && (argv[a][0] == '-'); a++) 
  {
    /* check for append mode */
    if (argv[a][1] == 'a')
    {
      mode = "a";
    }
    if (argv[a][1] == 't')
    {
      timestamper = "%H:%M:%S ";
    }
  }

  if ((a >= argc) || !argv[a]) 
  {
      usage();
  }
  if ((fd = fopen(argv[a], mode)) == NULL)
  {
    perror(argv[a]);
    exit(2);
  }

  /* OK we should now have stdin to read from, stout and fd to write to */
  while (fgets(buf,sizeof(buf),stdin))
  {
    /* send a copy to both the file and to standard output */
      fputs(buf,stdout);
      if (timestamper) 
      {
        time_p = time(&time_p);
	tm_p = localtime(&time_p);
	if (tm_p)
	{
	  strftime(tbuf, sizeof(tbuf), timestamper, tm_p);
	  fputs(tbuf,fd);
	}
      }
      fputs(buf,fd);
  }
  /* no more, so close and exit */
  fclose(fd);
  exit(0);
      
}