tail.c

HLPDK V10.0+ System Extension Library

	    lseek (fd, 0L, L_SET);
	  else
	    /* The file is longer than we want, so go back. */
	    lseek (fd, -number, L_XTND);
	  dump_remainder (filename, fd, mode);
	}
      else
	return pipe_bytes (filename, fd, number);
    }
  return 0;
}

/* Display the last part of file `filename', open for reading on `fd',
   using `number' lines, controlled by `mode'.
   Return 0 if successful, 1 if an error occurred. */

int
tail_lines (filename, fd, mode, number)
     char *filename;
     int fd;
     int mode;
     long number;
{
  struct stat stats;
  long length;

  if (fstat (fd, &stats))
    {
      error (0, errno, "%s", filename);
      return 1;
    }

  if (mode & START)
    {
      if (start_lines (filename, fd, number))
	return 1;
      dump_remainder (filename, fd, mode);
    }
  else
    {
      if ((stats.st_mode & S_IFMT) == S_IFREG)
	{
	  length = lseek (fd, 0L, L_XTND);
	  if (length != 0 && file_lines (filename, fd, number, length))
	    return 1;
	  dump_remainder (filename, fd, mode);
	}
      else
	return pipe_lines (filename, fd, number);
    }
  return 0;
}

/* Print the last `number' lines from the end of file `fd'.
   Go backward through the file, reading `BUFSIZE' bytes at a time (except
   probably the first), until we hit the start of the file or have
   read `number' newlines.
   `pos' starts out as the length of the file (the offset of the last
   byte of the file + 1).
   Return 0 if successful, 1 if an error occurred. */

int
file_lines (filename, fd, number, pos)
     char *filename;
     int fd;
     long number;
     long pos;
{
  char buffer[BUFSIZE];
  int bytes_read;
  int i;			/* Index into `buffer' for scanning. */

  if (number == 0)
    return 0;

  /* Set `bytes_read' to the size of the last, probably partial, buffer;
     0 < `bytes_read' <= `BUFSIZE'. */
#ifdef MSDOS				/* shut up the compiler */
  bytes_read = (int) (pos % (long) BUFSIZE);
#else
  bytes_read = pos % BUFSIZE;
#endif
  if (bytes_read == 0)
    bytes_read = BUFSIZE;
  /* Make `pos' a multiple of `BUFSIZE' (0 if the file is short), so that all
     reads will be on block boundaries, which might increase efficiency. */
  pos -= bytes_read;
  lseek (fd, pos, L_SET);
  bytes_read = read (fd, buffer, bytes_read);
  if (bytes_read == -1)
    {
      error (0, errno, "%s", filename);
      return 1;
    }

  /* Count the incomplete line on files that don't end with a newline. */
  if (bytes_read && buffer[bytes_read - 1] != '\n')
    --number;

  do
    {
      /* Scan backward, counting the newlines in this bufferfull. */
      for (i = bytes_read - 1; i >= 0; i--)
	{
	  /* Have we counted the requested number of newlines yet? */
	  if (buffer[i] == '\n' && number-- == 0)
	    {
	      /* If this newline wasn't the last character in the buffer,
	         print the text after it. */
	      if (i != bytes_read - 1)
		xwrite (1, &buffer[i + 1], bytes_read - (i + 1));
	      return 0;
	    }
	}
      /* Not enough newlines in that bufferfull. */
      if (pos == 0)
	{
	  /* Not enough lines in the file; print the entire file. */
	  lseek (fd, 0L, L_SET);
	  return 0;
	}
      pos -= BUFSIZE;
      lseek (fd, pos, L_SET);
    }
  while ((bytes_read = read (fd, buffer, BUFSIZE)) > 0);
  if (bytes_read == -1)
    {
      error (0, errno, "%s", filename);
      return 1;
    }
  return 0;
}

/* Print the last `number' lines from the end of the standard input,
   open for reading as pipe `fd'.
   Buffer the text as a linked list of LBUFFERs, adding them as needed.
   Return 0 if successful, 1 if an error occured. */

int
pipe_lines (filename, fd, number)
     char *filename;
     int fd;
     long number;
{
  struct linebuffer
  {
    int nbytes, nlines;
    char buffer[BUFSIZE];
    struct linebuffer *next;
  };
  typedef struct linebuffer LBUFFER;
  LBUFFER *first, *last, *tmp;
  int i;			/* Index into buffers. */
  long total_lines = 0;		/* Total number of newlines in all buffers. */
  int errors = 0;

  first = last = (LBUFFER *) xmalloc (sizeof (LBUFFER));
  first->nbytes = first->nlines = 0;
  tmp = (LBUFFER *) xmalloc (sizeof (LBUFFER));

  /* Input is always read into a fresh buffer. */
  while ((tmp->nbytes = read (fd, tmp->buffer, BUFSIZE)) > 0)
    {
      tmp->nlines = 0;
      tmp->next = NULL;

      /* Count the number of newlines just read. */
      for (i = 0; i < tmp->nbytes; i++)
	if (tmp->buffer[i] == '\n')
	  ++tmp->nlines;
      total_lines += tmp->nlines;

      /* If there is enough room in the last buffer read, just append the new
         one to it.  This is because when reading from a pipe, `nbytes' can
         often be very small. */
      if (tmp->nbytes + last->nbytes < BUFSIZE)
	{
	  bcopy (tmp->buffer, &last->buffer[last->nbytes], tmp->nbytes);
	  last->nbytes += tmp->nbytes;
	  last->nlines += tmp->nlines;
	}
      else
	{
	  /* If there's not enough room, link the new buffer onto the end of
	     the list, then either free up the oldest buffer for the next
	     read if that would leave enough lines, or else malloc a new one.
	     Some compaction mechanism is possible but probably not
	     worthwhile. */
	  last = last->next = tmp;
	  if (total_lines - first->nlines > number)
	    {
	      tmp = first;
	      total_lines -= first->nlines;
	      first = first->next;
	    }
	  else
	    tmp = (LBUFFER *) xmalloc (sizeof (LBUFFER));
	}
    }
  if (tmp->nbytes == -1)
    {
      error (0, errno, "%s", filename);
      errors = 1;
      free ((char *) tmp);
      goto free_lbuffers;
    }

  free ((char *) tmp);

  /* This prevents a core dump when the pipe contains no newlines. */
  if (number == 0)
    goto free_lbuffers;

  /* Count the incomplete line on files that don't end with a newline. */
  if (last->buffer[last->nbytes - 1] != '\n')
    {
      ++last->nlines;
      ++total_lines;
    }

  /* Run through the list, printing lines.  First, skip over unneeded
     buffers. */
  for (tmp = first; total_lines - tmp->nlines > number; tmp = tmp->next)
    total_lines -= tmp->nlines;

  /* Find the correct beginning, then print the rest of the file. */
  if (total_lines > number)
    {
      char *cp;

      /* Skip `total_lines' - `number' newlines.  We made sure that
         `total_lines' - `number' <= `tmp->nlines'. */
      cp = tmp->buffer;
#ifdef MSDOS				/* shut up the compiler */
      for (i = (int) (total_lines - number); i; --i)
#else
      for (i = total_lines - number; i; --i)
#endif
	while (*cp++ != '\n')
	  /* Do nothing. */ ;
      i = cp - tmp->buffer;
    }
  else
    i = 0;
  xwrite (1, &tmp->buffer[i], tmp->nbytes - i);

  for (tmp = tmp->next; tmp; tmp = tmp->next)
    xwrite (1, tmp->buffer, tmp->nbytes);

free_lbuffers:
  while (first)
    {
      tmp = first->next;
      free ((char *) first);
      first = tmp;
    }
  return errors;
}

/* Print the last `number' characters from the end of pipe `fd'.
   This is a stripped down version of pipe_lines.
   Return 0 if successful, 1 if an error occurred. */

int
pipe_bytes (filename, fd, number)
     char *filename;
     int fd;
     long number;
{
  struct charbuffer
  {
    int nbytes;
    char buffer[BUFSIZE];
    struct charbuffer *next;
  };
  typedef struct charbuffer CBUFFER;
  CBUFFER *first, *last, *tmp;
  int i;			/* Index into buffers. */
#ifdef MSDOS
  long total_bytes = 0;		/* Total characters in all buffers. */
#else
  int total_bytes = 0;		/* Total characters in all buffers. */
#endif
  int errors = 0;

  first = last = (CBUFFER *) xmalloc (sizeof (CBUFFER));
  first->nbytes = 0;
  tmp = (CBUFFER *) xmalloc (sizeof (CBUFFER));

  /* Input is always read into a fresh buffer. */
  while ((tmp->nbytes = read (fd, tmp->buffer, BUFSIZE)) > 0)
    {
      tmp->next = NULL;

      total_bytes += tmp->nbytes;
      /* If there is enough room in the last buffer read, just append the new
         one to it.  This is because when reading from a pipe, `nbytes' can
         often be very small. */
      if (tmp->nbytes + last->nbytes < BUFSIZE)
	{
	  bcopy (tmp->buffer, &last->buffer[last->nbytes], tmp->nbytes);
	  last->nbytes += tmp->nbytes;
	}
      else
	{
	  /* If there's not enough room, link the new buffer onto the end of
	     the list, then either free up the oldest buffer for the next
	     read if that would leave enough characters, or else malloc a new
	     one.  Some compaction mechanism is possible but probably not
	     worthwhile. */
	  last = last->next = tmp;
	  if (total_bytes - first->nbytes > number)
	    {
	      tmp = first;
	      total_bytes -= first->nbytes;
	      first = first->next;
	    }
	  else
	    {
	      tmp = (CBUFFER *) xmalloc (sizeof (CBUFFER));
	    }
	}
    }
  if (tmp->nbytes == -1)
    {
      error (0, errno, "%s", filename);
      errors = 1;
      free ((char *) tmp);
      goto free_cbuffers;
    }

  free ((char *) tmp);

  /* Run through the list, printing characters.  First, skip over unneeded
     buffers. */
  for (tmp = first; total_bytes - tmp->nbytes > number; tmp = tmp->next)
    total_bytes -= tmp->nbytes;

  /* Find the correct beginning, then print the rest of the file.
     We made sure that `total_bytes' - `number' <= `tmp->nbytes'. */
  if (total_bytes > number)
#ifdef MSDOS				/* shut up the compiler */
    i = (int) (total_bytes - number);
#else
    i = total_bytes - number;
#endif
  else
    i = 0;
  xwrite (1, &tmp->buffer[i], tmp->nbytes - i);

  for (tmp = tmp->next; tmp; tmp = tmp->next)
    xwrite (1, tmp->buffer, tmp->nbytes);

free_cbuffers:
  while (first)
    {
      tmp = first->next;
      free ((char *) first);
      first = tmp;
    }
  return errors;
}

/* Skip `number' characters from the start of pipe `fd', and print
   any extra characters that were read beyond that.
   Return 1 on error, 0 if ok.  */

int
start_bytes (filename, fd, number)
     char *filename;
     int fd;
     long number;
{
  char buffer[BUFSIZE];
  int bytes_read = 0;

  while (number > 0 && (bytes_read = read (fd, buffer, BUFSIZE)) > 0)
    number -= bytes_read;
  if (bytes_read == -1)
    {
      error (0, errno, "%s", filename);
      return 1;
    }
  else if (number < 0)
#ifdef MSDOS				/* |number| < 64k ??? */
    xwrite (1, &buffer[bytes_read + number], (unsigned int) (-number));
#else
    xwrite (1, &buffer[bytes_read + number], -number);
#endif
  return 0;
}

/* Skip `number' lines at the start of file or pipe `fd', and print
   any extra characters that were read beyond that.
   Return 1 on error, 0 if ok.  */

int
start_lines (filename, fd, number)
     char *filename;
     int fd;
     long number;
{
  char buffer[BUFSIZE];
  int bytes_read = 0;
  int bytes_to_skip = 0;

  while (number && (bytes_read = read (fd, buffer, BUFSIZE)) > 0)
    {
      bytes_to_skip = 0;
      while (bytes_to_skip < bytes_read)
	if (buffer[bytes_to_skip++] == '\n' && --number == 0)
	  break;
    }
  if (bytes_read == -1)
    {
      error (0, errno, "%s", filename);
      return 1;
    }
  else if (bytes_to_skip < bytes_read)
    xwrite (1, &buffer[bytes_to_skip], bytes_read - bytes_to_skip);
  return 0;
}

/* Display file `filename' from the current position in `fd'
   to the end.  If selected in `mode', keep reading from the
   end of the file until killed. */

void
dump_remainder (filename, fd, mode)
     char *filename;
     int fd;
     int mode;
{
  char buffer[BUFSIZE];
  int bytes_read;

output:
  while ((bytes_read = read (fd, buffer, BUFSIZE)) > 0)
    xwrite (1, buffer, bytes_read);
  if (bytes_read == -1)
    error (1, errno, "%s", filename);
#ifndef MSDOS
  if (mode & FOREVER)
    {
      sleep (1);
      goto output;
    }
#endif
}

/* Write plus error check. */

void
xwrite (fd, buffer, count)
     int fd;
     int count;
     char *buffer;
{
  fd = write (fd, buffer, count);
  if (fd != count)
    error (1, errno, "write error");
}

/* Allocate `size' bytes of memory dynamically, with error check. */

char *
xmalloc (size)
     int size;
{
  char *p;

  p = malloc ((unsigned) size);
  if (p == NULL)
    error (1, 0, "virtual memory exhausted");
  return p;
}

/* Convert `str', a string of ASCII digits, into an unsigned integer.
   Return -1 if `str' does not represent a valid unsigned integer. */

long
atou (str)
     char *str;
{
  unsigned long value;

  for (value = 0; ISDIGIT (*str); ++str)
    value = value * 10 + *str - '0';
  return *str ? -1L : value;
}

void
usage ()
{
#ifdef MSDOS
  fprintf (stderr, "\
Usage: %s [-b [+]#] [-c [+]#] [-n [+]#] [-fqvB] [+blocks [+]#]\n\
       [+bytes [+]#] [+lines [+]#] [+follow] [+quiet] [+silent]\n\
       [+verbose] [+binary] [+copying] [+version] [file...]\n\
\n\
       %s [+/-#bcflqv] [file...]\n", program_name, program_name);
  exit (1);
#else
  fprintf (stderr, "\
Usage: %s [-b [+]#] [-c [+]#] [-n [+]#] [-fqv] [+blocks [+]#]\n\
       [+bytes [+]#] [+lines [+]#] [+follow] [+quiet] [+silent]\n\
       [+verbose] [file...]\n\
\n\
       %s [+/-#bcflqv] [file...]\n", program_name, program_name);
  exit (1);
#endif
}