path: root/src/head.c

/* head -- output first part of file(s)
   Copyright (C) 89, 90, 91, 1995-2002 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.  */

/* Options: (see usage)
   Reads from standard input if no files are given or when a filename of
   ``-'' is encountered.
   By default, filename headers are printed only if more than one file
   is given.
   By default, prints the first 10 lines (head -n 10).

   David MacKenzie <djm@gnu.ai.mit.edu> */

#include <config.h>

#include <stdio.h>
#include <getopt.h>
#include <sys/types.h>
#include "system.h"
#include "closeout.h"
#include "error.h"
#include "posixver.h"
#include "xstrtol.h"
#include "safe-read.h"

/* The official name of this program (e.g., no `g' prefix).  */
#define PROGRAM_NAME "head"

#define AUTHORS "David MacKenzie"

/* Number of lines/chars/blocks to head. */
#define DEFAULT_NUMBER 10

/* Size of atomic reads. */
#define BUFSIZE (512 * 8)

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

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

/* Options corresponding to header_mode values.  */
static char const header_mode_option[][4] = { "", " -v", " -q" };

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

/* Have we ever read standard input?  */
static int have_read_stdin;

static struct option const long_options[] =
{
  {"bytes", required_argument, NULL, 'c'},
  {"lines", required_argument, NULL, 'n'},
  {"quiet", no_argument, NULL, 'q'},
  {"silent", no_argument, NULL, 'q'},
  {"verbose", no_argument, NULL, 'v'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

void
usage (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);
      fputs (_("\
Print first 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\
"), stdout);
      fputs (_("\
Mandatory arguments to long options are mandatory for short options too.\n\
"), stdout);
      fputs (_("\
  -c, --bytes=SIZE         print first SIZE bytes\n\
  -n, --lines=NUMBER       print first NUMBER lines instead of first 10\n\
"), stdout);
      fputs (_("\
  -q, --quiet, --silent    never print headers giving file names\n\
  -v, --verbose            always print headers giving file names\n\
"), stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      fputs (_("\
\n\
SIZE may have a multiplier suffix: b for 512, k for 1K, m for 1 Meg.\n\
"), stdout);
      printf (_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
    }
  exit (status == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
}

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

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

static int
head_bytes (const char *filename, int fd, uintmax_t bytes_to_write)
{
  char buffer[BUFSIZE];
  size_t bytes_to_read = BUFSIZE;

  /* Need BINARY I/O for the byte counts to be accurate.  */
  SET_BINARY2 (fd, fileno (stdout));

  while (bytes_to_write)
    {
      size_t bytes_read;
      if (bytes_to_write < bytes_to_read)
	bytes_to_read = bytes_to_write;
      bytes_read = safe_read (fd, buffer, bytes_to_read);
      if (bytes_read == SAFE_READ_ERROR)
	{
	  error (0, errno, "%s", filename);
	  return 1;
	}
      if (bytes_read == 0)
	break;
      if (fwrite (buffer, 1, bytes_read, stdout) == 0)
	error (EXIT_FAILURE, errno, _("write error"));
      bytes_to_write -= bytes_read;
    }
  return 0;
}

static int
head_lines (const char *filename, int fd, uintmax_t lines_to_write)
{
  char buffer[BUFSIZE];

  /* Need BINARY I/O for the byte counts to be accurate.  */
  SET_BINARY2 (fd, fileno (stdout));

  while (lines_to_write)
    {
      size_t bytes_read = safe_read (fd, buffer, BUFSIZE);
      size_t bytes_to_write = 0;

      if (bytes_read == SAFE_READ_ERROR)
	{
	  error (0, errno, "%s", filename);
	  return 1;
	}
      if (bytes_read == 0)
	break;
      while (bytes_to_write < bytes_read)
	if (buffer[bytes_to_write++] == '\n' && --lines_to_write == 0)
	  {
	    off_t n_bytes_past_EOL = bytes_read - bytes_to_write;
	    /* If we have read more data than that on the specified number
	       of lines, try to seek back to the position we would have
	       gotten to had we been reading one byte at a time.  */
	    if (lseek (fd, -n_bytes_past_EOL, SEEK_CUR) < 0)
	      {
		int e = errno;
		struct stat st;
		if (fstat (fd, &st) != 0 || S_ISREG (st.st_mode))
		  error (0, e, _("cannot reposition file pointer for %s"),
			 filename);
	      }
	    break;
	  }
      if (fwrite (buffer, 1, bytes_to_write, stdout) == 0)
	error (EXIT_FAILURE, errno, _("write error"));
    }
  return 0;
}

static int
head (const char *filename, int fd, uintmax_t n_units, int count_lines)
{
  if (print_headers)
    write_header (filename);

  if (count_lines)
    return head_lines (filename, fd, n_units);
  else
    return head_bytes (filename, fd, n_units);
}

static int
head_file (const char *filename, uintmax_t n_units, int count_lines)
{
  int fd;

  if (STREQ (filename, "-"))
    {
      have_read_stdin = 1;
      return head (_("standard input"), STDIN_FILENO, n_units, count_lines);
    }
  else
    {
      fd = open (filename, O_RDONLY);
      if (fd >= 0)
	{
	  int errors;

	  errors = head (filename, fd, n_units, count_lines);
	  if (close (fd) == 0)
	    return errors;
	}
      error (0, errno, "%s", filename);
      return 1;
    }
}

/* Convert a string of decimal digits, N_STRING, with a single, optional suffix
   character (b, k, or m) to an integral value.  Upon successful conversion,
   return that value.  If it cannot be converted, give a diagnostic and exit.
   COUNT_LINES indicates whether N_STRING is a number of bytes or a number
   of lines.  It is used solely to give a more specific diagnostic.  */

static uintmax_t
string_to_integer (int count_lines, const char *n_string)
{
  strtol_error s_err;
  uintmax_t n;

  s_err = xstrtoumax (n_string, NULL, 10, &n, "bkm");

  if (s_err == LONGINT_OVERFLOW)
    {
      error (EXIT_FAILURE, 0,
	     _("%s: %s is so large that it is not representable"), n_string,
	     count_lines ? _("number of lines") : _("number of bytes"));
    }

  if (s_err != LONGINT_OK)
    {
      error (EXIT_FAILURE, 0, "%s: %s", n_string,
	     (count_lines
	      ? _("invalid number of lines")
	      : _("invalid number of bytes")));
    }

  return n;
}

int
main (int argc, char **argv)
{
  enum header_mode header_mode = multiple_files;
  int exit_status = 0;
  int c;

  /* Number of items to print. */
  uintmax_t n_units = DEFAULT_NUMBER;

  /* If nonzero, interpret the numeric argument as the number of lines.
     Otherwise, interpret it as the number of bytes.  */
  int count_lines = 1;

  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  have_read_stdin = 0;

  print_headers = 0;

  if (1 < argc && argv[1][0] == '-' && ISDIGIT (argv[1][1]))
    {
      char *a = argv[1];
      char *n_string = ++a;
      char *end_n_string;
      char multiplier_char = 0;

      /* Old option syntax; a dash, one or more digits, and one or
	 more option letters.  Move past the number. */
      do ++a;
      while (ISDIGIT (*a));

      /* Pointer to the byte after the last digit.  */
      end_n_string = a;

      /* Parse any appended option letters. */
      for (; *a; a++)
	{
	  switch (*a)
	    {
	    case 'c':
	      count_lines = 0;
	      multiplier_char = 0;
	      break;

	    case 'b':
	    case 'k':
	    case 'm':
	      count_lines = 0;
	      multiplier_char = *a;
	      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'"), *a);
	      usage (EXIT_FAILURE);
	    }
	}

      if (200112 <= posix2_version ())
	{
	  error (0, 0, _("`-%s' option is obsolete; use `-%c %.*s%.*s%s'"),
		 n_string, count_lines ? 'n' : 'c',
		 (int) (end_n_string - n_string), n_string,
		 multiplier_char != 0, &multiplier_char,
		 header_mode_option[header_mode]);
	  usage (EXIT_FAILURE);
	}

      /* Append the multiplier character (if any) onto the end of
	 the digit string.  Then add NUL byte if necessary.  */
      *end_n_string = multiplier_char;
      if (multiplier_char)
	*(++end_n_string) = 0;

      n_units = string_to_integer (count_lines, n_string);

      /* Make the options we just parsed invisible to getopt. */
      argv[1] = argv[0];
      argv++;
      argc--;

      /* FIXME: allow POSIX options if there were obsolescent ones?  */

    }

  while ((c = getopt_long (argc, argv, "c:n:qv", long_options, NULL)) != -1)
    {
      switch (c)
	{
	case 0:
	  break;

	case 'c':
	  count_lines = 0;
	  n_units = string_to_integer (count_lines, optarg);
	  break;

	case 'n':
	  count_lines = 1;
	  n_units = string_to_integer (count_lines, optarg);
	  break;

	case 'q':
	  header_mode = never;
	  break;

	case 'v':
	  header_mode = always;
	  break;

	case_GETOPT_HELP_CHAR;

	case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);

	default:
	  usage (EXIT_FAILURE);
	}
    }

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

  if (optind == argc)
    exit_status |= head_file ("-", n_units, count_lines);

  for (; optind < argc; ++optind)
    exit_status |= head_file (argv[optind], n_units, count_lines);

  if (have_read_stdin && close (STDIN_FILENO) < 0)
    error (EXIT_FAILURE, errno, "-");

  exit (exit_status == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
}