.

[coreutils.git] / src / tail.c

/* tail -- output the last part of file(s)
   Copyright (C) 1989, 1990, 1991, 1995 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* Can display any amount of data, unlike the Unix version, which uses
   a fixed size buffer and therefore can only deliver a limited number
   of lines.

   Options:
   -b                   Tail by N 512-byte blocks.
   -c, --bytes=N[bkm]   Tail by N bytes
                        [or 512-byte blocks, kilobytes, or megabytes].
   -f, --follow         Loop forever trying to read more characters at the
                        end of the file, on the assumption that the file
                        is growing.  Ignored if reading from a pipe.
   -n, --lines=N        Tail by N lines.
   -q, --quiet, --silent        Never print filename headers.
   -v, --verbose                Always print filename headers.

   If a number (N) starts with a `+', begin printing with the Nth item
   from the start of each file, instead of from the end.

   Reads from standard input if no files are given or when a filename of
   ``-'' is encountered.
   By default, filename headers are printed only more than one file
   is given.
   By default, prints the last 10 lines (tail -n 10).

   Original version by Paul Rubin <phr@ocf.berkeley.edu>.
   Extensions by David MacKenzie <djm@gnu.ai.mit.edu>.
   tail -f for multiple files by Ian Lance Taylor <ian@airs.com>.  */

#include <config.h>

#include <stdio.h>
#include <assert.h>
#include <getopt.h>
#include <sys/types.h>

#include "system.h"
#include "version.h"
#include "xstrtol.h"
#include "error.h"

/* Disable assertions.  Some systems have broken assert macros.  */
#define NDEBUG 1

#define XWRITE(fd, buffer, n_bytes)                                     \
  do                                                                    \
    {                                                                   \
      assert ((fd) == 1);                                               \
      assert ((n_bytes) >= 0);                                          \
      if (n_bytes > 0 && fwrite ((buffer), 1, (n_bytes), stdout) == 0)  \
        error (1, errno, "write error");                                \
    }                                                                   \
  while (0)

/* Number of items to tail.  */
#define DEFAULT_N_LINES 10

/* Size of atomic reads.  */
#ifndef BUFSIZ
#define BUFSIZ (512 * 8)
#endif

/* If nonzero, interpret the numeric argument as the number of lines.
   Otherwise, interpret it as the number of bytes.  */
static int count_lines;

/* If nonzero, read from the end of one file until killed.  */
static int forever;

/* If nonzero, read from the end of multiple files until killed.  */
static int forever_multiple;

/* Array of file descriptors if forever_multiple is 1.  */
static int *file_descs;

/* Array of file sizes if forever_multiple is 1.  */
static off_t *file_sizes;

/* If nonzero, count from start of file instead of end.  */
static int from_start;

/* If nonzero, print filename headers.  */
static int print_headers;

/* When to print the filename banners.  */
enum header_mode
{
  multiple_files, always, never
};

char *xmalloc ();
int safe_read ();

static int file_lines ();
static int pipe_bytes ();
static int pipe_lines ();
static int start_bytes ();
static int start_lines ();
static int tail ();
static int tail_bytes ();
static int tail_file ();
static int tail_lines ();
static long dump_remainder ();
static void tail_forever ();
static void usage ();
static void write_header ();

/* The name this program was run with.  */
char *program_name;

/* Nonzero if we have ever read standard input.  */
static int have_read_stdin;

/* If non-zero, display usage information and exit.  */
static int show_help;

/* If non-zero, print the version on standard output then exit.  */
static int show_version;

static struct option const long_options[] =
{
  {"bytes", required_argument, NULL, 'c'},
  {"follow", no_argument, NULL, 'f'},
  {"lines", required_argument, NULL, 'n'},
  {"quiet", no_argument, NULL, 'q'},
  {"silent", no_argument, NULL, 'q'},
  {"verbose", no_argument, NULL, 'v'},
  {"help", no_argument, &show_help, 1},
  {"version", no_argument, &show_version, 1},
  {NULL, 0, NULL, 0}
};

void
main (argc, argv)
     int argc;
     char **argv;
{
  enum header_mode header_mode = multiple_files;
  int exit_status = 0;
  /* If from_start, the number of items to skip before printing; otherwise,
     the number of items at the end of the file to print.  Initially, -1
     means the value has not been set.  */
  off_t n_units = -1;
  long int tmp_long;
  int c;                        /* Option character.  */
  int fileind;                  /* Index in ARGV of first file name.  */

  program_name = argv[0];
  have_read_stdin = 0;
  count_lines = 1;
  forever = forever_multiple = from_start = print_headers = 0;

  if (argc > 1
      && ((argv[1][0] == '-' && ISDIGIT (argv[1][1]))
          || (argv[1][0] == '+' && (ISDIGIT (argv[1][1]) || argv[1][1] == 0))))
    {
      /* Old option syntax: a dash or plus, one or more digits (zero digits
         are acceptable with a plus), and one or more option letters.  */
      if (argv[1][0] == '+')
        from_start = 1;
      if (argv[1][1] != '\0')
        {
          strtol_error s_err;
          char *p;

          s_err = xstrtol (++argv[1], &p, 0, &tmp_long, "bkm");
          n_units = tmp_long;
          if (s_err == LONGINT_OVERFLOW)
            {
              STRTOL_FATAL_ERROR (argv[1], "argument", s_err);
            }
          /* Parse any appended option letters.  */
          while (*p)
            {
              switch (*p)
                {
                case 'c':
                  /* Interpret N_UNITS as # of bytes.  */
                  count_lines = 0;
                  break;

                case 'f':
                  forever = 1;
                  break;

                case 'l':
                  count_lines = 1;
                  break;

                case 'q':
                  header_mode = never;
                  break;

                case 'v':
                  header_mode = always;
                  break;

                default:
                  error (0, 0, "unrecognized option `-%c'", *p);
                  usage (1);
                }
              ++p;
            }
        }
      /* Make the options we just parsed invisible to getopt.  */
      argv[1] = argv[0];
      argv++;
      argc--;
    }

  while ((c = getopt_long (argc, argv, "c:n:fqv", long_options, (int *) 0))
         != EOF)
    {
      strtol_error s_err;

      switch (c)
        {
        case 0:
          break;

        case 'c':
          count_lines = 0;
          goto getnum;

        case 'n':
          count_lines = 1;
        getnum:
          if (*optarg == '+')
            {
              from_start = 1;
            }

          s_err = xstrtol (optarg, NULL, 0, &tmp_long, "bkm");
          if (tmp_long < 0)
            tmp_long = -tmp_long;
          n_units = tmp_long;
          if (s_err != LONGINT_OK)
            {
              STRTOL_FATAL_ERROR (optarg, (c == 'n'
                                           ? "number of lines"
                                           : "number of bytes"), s_err);
            }
          break;

        case 'f':
          forever = 1;
          break;

        case 'q':
          header_mode = never;
          break;

        case 'v':
          header_mode = always;
          break;

        default:
          usage (1);
        }
    }

  if (show_version)
    {
      printf ("tail - %s\n", version_string);
      exit (0);
    }

  if (show_help)
    usage (0);

  if (n_units == -1)
    n_units = DEFAULT_N_LINES;

  /* To start printing with item N_UNITS from the start of the file, skip
     N_UNITS - 1 items.  `tail +0' is actually meaningless, but for Unix
     compatibility it's treated the same as `tail +1'.  */
  if (from_start)
    {
      if (n_units)
        --n_units;
    }

  fileind = optind;

  if (optind < argc - 1 && forever)
    {
      forever_multiple = 1;
      forever = 0;
      file_descs = (int *) xmalloc ((argc - optind) * sizeof (int));
      file_sizes = (off_t *) xmalloc ((argc - optind) * sizeof (off_t));
    }

  if (header_mode == always
      || (header_mode == multiple_files && optind < argc - 1))
    print_headers = 1;

  if (optind == argc)
    exit_status |= tail_file ("-", n_units, 0);

  for (; optind < argc; ++optind)
    exit_status |= tail_file (argv[optind], n_units, optind - fileind);

  if (forever_multiple)
    tail_forever (argv + fileind, argc - fileind);

  if (have_read_stdin && close (0) < 0)
    error (1, errno, "-");
  if (fclose (stdout) == EOF)
    error (1, errno, "write error");
  exit (exit_status);
}

/* Display the last N_UNITS units of file FILENAME.
   "-" for FILENAME means the standard input.
   FILENUM is this file's index in the list of files the user gave.
   Return 0 if successful, 1 if an error occurred.  */

static int
tail_file (filename, n_units, filenum)
     const char *filename;
     off_t n_units;
     int filenum;
{
  int fd, errors;
  struct stat stats;

  if (!strcmp (filename, "-"))
    {
      have_read_stdin = 1;
      filename = "standard input";
      if (print_headers)
        write_header (filename, NULL);
      errors = tail (filename, 0, n_units);
      if (forever_multiple)
        {
          if (fstat (0, &stats) < 0)
            {
              error (0, errno, "standard input");
              errors = 1;
            }
          else if (!S_ISREG (stats.st_mode))
            {
              error (0, 0,
                     "standard input: cannot follow end of non-regular file");
              errors = 1;
            }
          if (errors)
            file_descs[filenum] = -1;
          else
            {
              file_descs[filenum] = 0;
              file_sizes[filenum] = stats.st_size;
            }
        }
    }
  else
    {
      /* Not standard input.  */
      fd = open (filename, O_RDONLY);
      if (fd == -1)
        {
          if (forever_multiple)
            file_descs[filenum] = -1;
          error (0, errno, "%s", filename);
          errors = 1;
        }
      else
        {
          if (print_headers)
            write_header (filename, NULL);
          errors = tail (filename, fd, n_units);
          if (forever_multiple)
            {
              if (fstat (fd, &stats) < 0)
                {
                  error (0, errno, "%s", filename);
                  errors = 1;
                }
              else if (!S_ISREG (stats.st_mode))
                {
                  error (0, 0, "%s: cannot follow end of non-regular file",
                         filename);
                  errors = 1;
                }
              if (errors)
                {
                  close (fd);
                  file_descs[filenum] = -1;
                }
              else
                {
                  file_descs[filenum] = fd;
                  file_sizes[filenum] = stats.st_size;
                }
            }
          else
            {
              if (close (fd))
                {
                  error (0, errno, "%s", filename);
                  errors = 1;
                }
            }
        }
    }

  return errors;
}

static void
write_header (filename, comment)
     const char *filename;
     const char *comment;
{
  static int first_file = 1;

  printf ("%s==> %s%s%s <==\n", (first_file ? "" : "\n"), filename,
          (comment ? ": " : ""),
          (comment ? comment : ""));
  first_file = 0;
}

/* Display the last N_UNITS units of file FILENAME, open for reading
   in FD.
   Return 0 if successful, 1 if an error occurred.  */

static int
tail (filename, fd, n_units)
     const char *filename;
     int fd;
     off_t n_units;
{
  if (count_lines)
    return tail_lines (filename, fd, n_units);
  else
    return tail_bytes (filename, fd, n_units);
}

/* Output the last N_BYTES bytes of file FILENAME open for reading in FD.
   Return 0 if successful, 1 if an error occurred.  */

static int
tail_bytes (filename, fd, n_bytes)
     const char *filename;
     int fd;
     off_t n_bytes;
{
  struct stat stats;

  /* FIXME: resolve this like in dd.c.  */
  /* Use fstat instead of checking for errno == ESPIPE because
     lseek doesn't work on some special files but doesn't return an
     error, either.  */
  if (fstat (fd, &stats))
    {
      error (0, errno, "%s", filename);
      return 1;
    }

  if (from_start)
    {
      if (S_ISREG (stats.st_mode))
        lseek (fd, n_bytes, SEEK_SET);
      else if (start_bytes (filename, fd, n_bytes))
        return 1;
      dump_remainder (filename, fd);
    }
  else
    {
      if (S_ISREG (stats.st_mode))
        {
          if (lseek (fd, (off_t) 0, SEEK_END) <= n_bytes)
            /* The file is shorter than we want, or just the right size, so
               print the whole file.  */
            lseek (fd, (off_t) 0, SEEK_SET);
          else
            /* The file is longer than we want, so go back.  */
            lseek (fd, -n_bytes, SEEK_END);
          dump_remainder (filename, fd);
        }
      else
        return pipe_bytes (filename, fd, n_bytes);
    }
  return 0;
}

/* Output the last N_LINES lines of file FILENAME open for reading in FD.
   Return 0 if successful, 1 if an error occurred.  */

static int
tail_lines (filename, fd, n_lines)
     const char *filename;
     int fd;
     long n_lines;
{
  struct stat stats;
  off_t length;

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

  if (from_start)
    {
      if (start_lines (filename, fd, n_lines))
        return 1;
      dump_remainder (filename, fd);
    }
  else
    {
      if (S_ISREG (stats.st_mode))
        {
          length = lseek (fd, (off_t) 0, SEEK_END);
          if (length != 0 && file_lines (filename, fd, n_lines, length))
            return 1;
          dump_remainder (filename, fd);
        }
      else
        return pipe_lines (filename, fd, n_lines);
    }
  return 0;
}

/* Print the last N_LINES lines from the end of file FD.
   Go backward through the file, reading `BUFSIZ' 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.  */

static int
file_lines (filename, fd, n_lines, pos)
     const char *filename;
     int fd;
     long n_lines;
     off_t pos;
{
  char buffer[BUFSIZ];
  int bytes_read;
  int i;                        /* Index into `buffer' for scanning.  */

  if (n_lines == 0)
    return 0;

  /* Set `bytes_read' to the size of the last, probably partial, buffer;
     0 < `bytes_read' <= `BUFSIZ'.  */
  bytes_read = pos % BUFSIZ;
  if (bytes_read == 0)
    bytes_read = BUFSIZ;
  /* Make `pos' a multiple of `BUFSIZ' (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, SEEK_SET);
  bytes_read = safe_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')
    --n_lines;

  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' && n_lines-- == 0)
            {
              /* If this newline wasn't the last character in the buffer,
                 print the text after it.  */
              if (i != bytes_read - 1)
                XWRITE (STDOUT_FILENO, &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, (off_t) 0, SEEK_SET);
          return 0;
        }
      pos -= BUFSIZ;
      lseek (fd, pos, SEEK_SET);
    }
  while ((bytes_read = safe_read (fd, buffer, BUFSIZ)) > 0);
  if (bytes_read == -1)
    {
      error (0, errno, "%s", filename);
      return 1;
    }
  return 0;
}

/* Print the last N_LINES 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.  */

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

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

  /* Input is always read into a fresh buffer.  */
  while ((tmp->nbytes = safe_read (fd, tmp->buffer, BUFSIZ)) > 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 < BUFSIZ)
        {
          memcpy (&last->buffer[last->nbytes], tmp->buffer, 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 > n_lines)
            {
              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 (n_lines == 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 > n_lines; tmp = tmp->next)
    total_lines -= tmp->nlines;

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

      /* Skip `total_lines' - `n_lines' newlines.  We made sure that
         `total_lines' - `n_lines' <= `tmp->nlines'.  */
      cp = tmp->buffer;
      for (i = total_lines - n_lines; i; --i)
        while (*cp++ != '\n')
          /* Do nothing.  */ ;
      i = cp - tmp->buffer;
    }
  else
    i = 0;
  XWRITE (STDOUT_FILENO, &tmp->buffer[i], tmp->nbytes - i);

  for (tmp = tmp->next; tmp; tmp = tmp->next)
    XWRITE (STDOUT_FILENO, tmp->buffer, tmp->nbytes);

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

/* Print the last N_BYTES 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.  */

static int
pipe_bytes (filename, fd, n_bytes)
     const char *filename;
     int fd;
     off_t n_bytes;
{
  struct charbuffer
  {
    int nbytes;
    char buffer[BUFSIZ];
    struct charbuffer *next;
  };
  typedef struct charbuffer CBUFFER;
  CBUFFER *first, *last, *tmp;
  int i;                        /* Index into buffers.  */
  int total_bytes = 0;          /* Total characters in all buffers.  */
  int errors = 0;

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

  /* Input is always read into a fresh buffer.  */
  while ((tmp->nbytes = safe_read (fd, tmp->buffer, BUFSIZ)) > 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 < BUFSIZ)
        {
          memcpy (&last->buffer[last->nbytes], tmp->buffer, 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 > n_bytes)
            {
              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 > n_bytes; tmp = tmp->next)
    total_bytes -= tmp->nbytes;

  /* Find the correct beginning, then print the rest of the file.
     We made sure that `total_bytes' - `n_bytes' <= `tmp->nbytes'.  */
  if (total_bytes > n_bytes)
    i = total_bytes - n_bytes;
  else
    i = 0;
  XWRITE (STDOUT_FILENO, &tmp->buffer[i], tmp->nbytes - i);

  for (tmp = tmp->next; tmp; tmp = tmp->next)
    XWRITE (STDOUT_FILENO, tmp->buffer, tmp->nbytes);

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

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

static int
start_bytes (filename, fd, n_bytes)
     const char *filename;
     int fd;
     off_t n_bytes;
{
  char buffer[BUFSIZ];
  int bytes_read = 0;

  while (n_bytes > 0 && (bytes_read = safe_read (fd, buffer, BUFSIZ)) > 0)
    n_bytes -= bytes_read;
  if (bytes_read == -1)
    {
      error (0, errno, "%s", filename);
      return 1;
    }
  else if (n_bytes < 0)
    XWRITE (STDOUT_FILENO, &buffer[bytes_read + n_bytes], -n_bytes);
  return 0;
}

/* Skip N_LINES 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.  */

static int
start_lines (filename, fd, n_lines)
     const char *filename;
     int fd;
     long n_lines;
{
  char buffer[BUFSIZ];
  int bytes_read = 0;
  int bytes_to_skip = 0;

  while (n_lines && (bytes_read = safe_read (fd, buffer, BUFSIZ)) > 0)
    {
      bytes_to_skip = 0;
      while (bytes_to_skip < bytes_read)
        if (buffer[bytes_to_skip++] == '\n' && --n_lines == 0)
          break;
    }
  if (bytes_read == -1)
    {
      error (0, errno, "%s", filename);
      return 1;
    }
  else if (bytes_to_skip < bytes_read)
    {
      XWRITE (STDOUT_FILENO, &buffer[bytes_to_skip],
              bytes_read - bytes_to_skip);
    }
  return 0;
}

/* Display file FILENAME from the current position in FD to the end.
   If `forever' is nonzero, keep reading from the end of the file
   until killed.  Return the number of bytes read from the file.  */

static long
dump_remainder (filename, fd)
     const char *filename;
     int fd;
{
  char buffer[BUFSIZ];
  int bytes_read;
  long total;

  total = 0;
output:
  while ((bytes_read = safe_read (fd, buffer, BUFSIZ)) > 0)
    {
      XWRITE (STDOUT_FILENO, buffer, bytes_read);
      total += bytes_read;
    }
  if (bytes_read == -1)
    error (1, errno, "%s", filename);
  if (forever)
    {
      fflush (stdout);
      sleep (1);
      goto output;
    }
  return total;
}

/* Tail NFILES (>1) files forever until killed.  The file names are in
   NAMES.  The open file descriptors are in `file_descs', and the size
   at which we stopped tailing them is in `file_sizes'.  We loop over
   each of them, doing an fstat to see if they have changed size.  If
   none of them have changed size in one iteration, we sleep for a
   second and try again.  We do this until the user interrupts us.  */

static void
tail_forever (names, nfiles)
     char **names;
     int nfiles;
{
  int last;

  last = -1;

  while (1)
    {
      int i;
      int changed;

      changed = 0;
      for (i = 0; i < nfiles; i++)
        {
          struct stat stats;

          if (file_descs[i] < 0)
            continue;
          if (fstat (file_descs[i], &stats) < 0)
            {
              error (0, errno, "%s", names[i]);
              file_descs[i] = -1;
              continue;
            }
          if (stats.st_size == file_sizes[i])
            continue;

          /* This file has changed size.  Print out what we can, and
             then keep looping.  */

          changed = 1;

          if (stats.st_size < file_sizes[i])
            {
              write_header (names[i], "file truncated");
              last = i;
              lseek (file_descs[i], stats.st_size, SEEK_SET);
              file_sizes[i] = stats.st_size;
              continue;
            }

          if (i != last)
            {
              if (print_headers)
                write_header (names[i], NULL);
              last = i;
            }
          file_sizes[i] += dump_remainder (names[i], file_descs[i]);
        }

      /* If none of the files changed size, sleep.  */
      if (! changed)
        sleep (1);
    }
}

static void
usage (status)
     int status;
{
  if (status != 0)
    fprintf (stderr, "Try `%s --help' for more information.\n",
             program_name);
  else
    {
      printf ("\
Usage: %s [OPTION]... [FILE]...\n\
",
              program_name);
      printf ("\
Print last 10 lines of each FILE to standard output.\n\
With more than one FILE, precede each with a header giving the file name.\n\
With no FILE, or when FILE is -, read standard input.\n\
\n\
  -c, --bytes=N            output the last N bytes\n\
  -f, --follow             output appended data as the file grows\n\
  -n, --lines=N            output the last N lines, instead of last 10\n\
  -q, --quiet, --silent    never output headers giving file names\n\
  -v, --verbose            always output headers giving file names\n\
      --help               display this help and exit\n\
      --version            output version information and exit\n\
\n\
If the first character of N (the number of bytes or lines) is a `+',\n\
print beginning with the Nth item from the start of each file, otherwise,\n\
print the last N items in the file.  N may have a multiplier suffix:\n\
b for 512, k for 1024, m for 1048576 (1 Meg).  A first OPTION of -VALUE\n\
or +VALUE is treated like -n VALUE or -n +VALUE unless VALUE has one of\n\
the [bkm] suffix multipliers, in which case it is treated like -c VALUE\n\
or -c +VALUE.\n\
");
    }
  exit (status);
}