/* join - join lines of two files on a common field
   Copyright (C) 91, 1995-2005 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

   Written by Mike Haertel, mike@gnu.ai.mit.edu.  */

#include <config.h>

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

#include "system.h"
#include "error.h"
#include "hard-locale.h"
#include "linebuffer.h"
#include "memcasecmp.h"
#include "quote.h"
#include "stdio-safer.h"
#include "xmemcoll.h"
#include "xstrtol.h"

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

#define AUTHORS "Mike Haertel"

#define join system_join

/* An element of the list identifying which fields to print for each
   output line.  */
struct outlist
  {
    /* File number: 0, 1, or 2.  0 means use the join field.
       1 means use the first file argument, 2 the second.  */
    int file;

    /* Field index (zero-based), specified only when FILE is 1 or 2.  */
    size_t field;

    struct outlist *next;
  };

/* A field of a line.  */
struct field
  {
    char *beg;			/* First character in field.  */
    size_t len;			/* The length of the field.  */
  };

/* A line read from an input file.  */
struct line
  {
    struct linebuffer buf;	/* The line itself.  */
    size_t nfields;		/* Number of elements in `fields'.  */
    size_t nfields_allocated;	/* Number of elements allocated for `fields'. */
    struct field *fields;
  };

/* One or more consecutive lines read from a file that all have the
   same join field value.  */
struct seq
  {
    size_t count;			/* Elements used in `lines'.  */
    size_t alloc;			/* Elements allocated in `lines'.  */
    struct line *lines;
  };

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

/* True if the LC_COLLATE locale is hard.  */
static bool hard_LC_COLLATE;

/* If nonzero, print unpairable lines in file 1 or 2.  */
static bool print_unpairables_1, print_unpairables_2;

/* If nonzero, print pairable lines.  */
static bool print_pairables;

/* Empty output field filler.  */
static char const *empty_filler;

/* Field to join on; SIZE_MAX means they haven't been determined yet.  */
static size_t join_field_1 = SIZE_MAX;
static size_t join_field_2 = SIZE_MAX;

/* List of fields to print.  */
static struct outlist outlist_head;

/* Last element in `outlist', where a new element can be added.  */
static struct outlist *outlist_end = &outlist_head;

/* Tab character separating fields.  If negative, fields are separated
   by any nonempty string of blanks, otherwise by exactly one
   tab character whose value (when cast to unsigned char) equals TAB.  */
static int tab = -1;

static struct option const longopts[] =
{
  {"ignore-case", no_argument, NULL, 'i'},
  {GETOPT_HELP_OPTION_DECL},
  {GETOPT_VERSION_OPTION_DECL},
  {NULL, 0, NULL, 0}
};

/* Used to print non-joining lines */
static struct line uni_blank;

/* If nonzero, ignore case when comparing join fields.  */
static bool ignore_case;

void
usage (int status)
{
  if (status != EXIT_SUCCESS)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
	     program_name);
  else
    {
      printf (_("\
Usage: %s [OPTION]... FILE1 FILE2\n\
"),
	      program_name);
      fputs (_("\
For each pair of input lines with identical join fields, write a line to\n\
standard output.  The default join field is the first, delimited\n\
by whitespace.  When FILE1 or FILE2 (not both) is -, read standard input.\n\
\n\
  -a FILENUM        print unpairable lines coming from file FILENUM, where\n\
                      FILENUM is 1 or 2, corresponding to FILE1 or FILE2\n\
  -e EMPTY          replace missing input fields with EMPTY\n\
"), stdout);
      fputs (_("\
  -i, --ignore-case ignore differences in case when comparing fields\n\
  -j FIELD          equivalent to `-1 FIELD -2 FIELD'\n\
  -o FORMAT         obey FORMAT while constructing output line\n\
  -t CHAR           use CHAR as input and output field separator\n\
"), stdout);
      fputs (_("\
  -v FILENUM        like -a FILENUM, but suppress joined output lines\n\
  -1 FIELD          join on this FIELD of file 1\n\
  -2 FIELD          join on this FIELD of file 2\n\
"), stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      fputs (_("\
\n\
Unless -t CHAR is given, leading blanks separate fields and are ignored,\n\
else fields are separated by CHAR.  Any FIELD is a field number counted\n\
from 1.  FORMAT is one or more comma or blank separated specifications,\n\
each being `FILENUM.FIELD' or `0'.  Default FORMAT outputs the join field,\n\
the remaining fields from FILE1, the remaining fields from FILE2, all\n\
separated by CHAR.\n\
\n\
Important: FILE1 and FILE2 must be sorted on the join fields.\n\
"), stdout);
      printf (_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
    }
  exit (status);
}

/* Return true if C is a blank (a default input field separator).  */

static inline bool
is_blank (unsigned char c)
{
  return ISBLANK (c) != 0;
}

/* Record a field in LINE, with location FIELD and size LEN.  */

static void
extract_field (struct line *line, char *field, size_t len)
{
  if (line->nfields >= line->nfields_allocated)
    {
      line->fields = x2nrealloc (line->fields, &line->nfields_allocated,
				 sizeof (struct field));
    }
  line->fields[line->nfields].beg = field;
  line->fields[line->nfields].len = len;
  ++(line->nfields);
}

/* Fill in the `fields' structure in LINE.  */

static void
xfields (struct line *line)
{
  char *ptr = line->buf.buffer;
  char const *lim = ptr + line->buf.length - 1;

  if (ptr == lim)
    return;

  if (0 <= tab)
    {
      char *sep;
      for (; (sep = memchr (ptr, tab, lim - ptr)) != NULL; ptr = sep + 1)
	extract_field (line, ptr, sep - ptr);
    }
  else
    {
      /* Skip leading blanks before the first field.  */
      while (is_blank (*ptr))
	if (++ptr == lim)
	  return;

      do
	{
	  char *sep;
	  for (sep = ptr + 1; sep != lim && ! is_blank (*sep); sep++)
	    continue;
	  extract_field (line, ptr, sep - ptr);
	  if (sep == lim)
	    return;
	  for (ptr = sep + 1; ptr != lim && is_blank (*ptr); ptr++)
	    continue;
	}
      while (ptr != lim);
    }

  extract_field (line, ptr, lim - ptr);
}

/* Read a line from FP into LINE and split it into fields.
   Return true if successful.  */

static bool
get_line (FILE *fp, struct line *line)
{
  initbuffer (&line->buf);

  if (! readlinebuffer (&line->buf, fp))
    {
      if (ferror (fp))
	error (EXIT_FAILURE, errno, _("read error"));
      free (line->buf.buffer);
      line->buf.buffer = NULL;
      return false;
    }

  line->nfields_allocated = 0;
  line->nfields = 0;
  line->fields = NULL;
  xfields (line);
  return true;
}

static void
freeline (struct line *line)
{
  free (line->fields);
  free (line->buf.buffer);
  line->buf.buffer = NULL;
}

static void
initseq (struct seq *seq)
{
  seq->count = 0;
  seq->alloc = 0;
  seq->lines = NULL;
}

/* Read a line from FP and add it to SEQ.  Return true if successful.  */

static bool
getseq (FILE *fp, struct seq *seq)
{
  if (seq->count == seq->alloc)
    seq->lines = x2nrealloc (seq->lines, &seq->alloc, sizeof *seq->lines);

  if (get_line (fp, &seq->lines[seq->count]))
    {
      ++seq->count;
      return true;
    }
  return false;
}

static void
delseq (struct seq *seq)
{
  size_t i;
  for (i = 0; i < seq->count; i++)
    if (seq->lines[i].buf.buffer)
      freeline (&seq->lines[i]);
  free (seq->lines);
}

/* Return <0 if the join field in LINE1 compares less than the one in LINE2;
   >0 if it compares greater; 0 if it compares equal.
   Report an error and exit if the comparison fails.  */

static int
keycmp (struct line const *line1, struct line const *line2)
{
  /* Start of field to compare in each file.  */
  char *beg1;
  char *beg2;

  size_t len1;
  size_t len2;		/* Length of fields to compare.  */
  int diff;

  if (join_field_1 < line1->nfields)
    {
      beg1 = line1->fields[join_field_1].beg;
      len1 = line1->fields[join_field_1].len;
    }
  else
    {
      beg1 = NULL;
      len1 = 0;
    }

  if (join_field_2 < line2->nfields)
    {
      beg2 = line2->fields[join_field_2].beg;
      len2 = line2->fields[join_field_2].len;
    }
  else
    {
      beg2 = NULL;
      len2 = 0;
    }

  if (len1 == 0)
    return len2 == 0 ? 0 : -1;
  if (len2 == 0)
    return 1;

  if (ignore_case)
    {
      /* FIXME: ignore_case does not work with NLS (in particular,
         with multibyte chars).  */
      diff = memcasecmp (beg1, beg2, MIN (len1, len2));
    }
  else
    {
      if (hard_LC_COLLATE)
	return xmemcoll (beg1, len1, beg2, len2);
      diff = memcmp (beg1, beg2, MIN (len1, len2));
    }

  if (diff)
    return diff;
  return len1 < len2 ? -1 : len1 != len2;
}

/* Print field N of LINE if it exists and is nonempty, otherwise
   `empty_filler' if it is nonempty.  */

static void
prfield (size_t n, struct line const *line)
{
  size_t len;

  if (n < line->nfields)
    {
      len = line->fields[n].len;
      if (len)
	fwrite (line->fields[n].beg, 1, len, stdout);
      else if (empty_filler)
	fputs (empty_filler, stdout);
    }
  else if (empty_filler)
    fputs (empty_filler, stdout);
}

/* Print the join of LINE1 and LINE2.  */

static void
prjoin (struct line const *line1, struct line const *line2)
{
  const struct outlist *outlist;
  char output_separator = tab < 0 ? ' ' : tab;

  outlist = outlist_head.next;
  if (outlist)
    {
      const struct outlist *o;

      o = outlist;
      while (1)
	{
	  size_t field;
	  struct line const *line;

	  if (o->file == 0)
	    {
	      if (line1 == &uni_blank)
	        {
		  line = line2;
		  field = join_field_2;
		}
	      else
	        {
		  line = line1;
		  field = join_field_1;
		}
	    }
	  else
	    {
	      line = (o->file == 1 ? line1 : line2);
	      field = o->field;
	    }
	  prfield (field, line);
	  o = o->next;
	  if (o == NULL)
	    break;
	  putchar (output_separator);
	}
      putchar ('\n');
    }
  else
    {
      size_t i;

      if (line1 == &uni_blank)
	{
	  struct line const *t;
	  t = line1;
	  line1 = line2;
	  line2 = t;
	}
      prfield (join_field_1, line1);
      for (i = 0; i < join_field_1 && i < line1->nfields; ++i)
	{
	  putchar (output_separator);
	  prfield (i, line1);
	}
      for (i = join_field_1 + 1; i < line1->nfields; ++i)
	{
	  putchar (output_separator);
	  prfield (i, line1);
	}

      for (i = 0; i < join_field_2 && i < line2->nfields; ++i)
	{
	  putchar (output_separator);
	  prfield (i, line2);
	}
      for (i = join_field_2 + 1; i < line2->nfields; ++i)
	{
	  putchar (output_separator);
	  prfield (i, line2);
	}
      putchar ('\n');
    }
}

/* Print the join of the files in FP1 and FP2.  */

static void
join (FILE *fp1, FILE *fp2)
{
  struct seq seq1, seq2;
  struct line line;
  int diff;
  bool eof1, eof2;

  /* Read the first line of each file.  */
  initseq (&seq1);
  getseq (fp1, &seq1);
  initseq (&seq2);
  getseq (fp2, &seq2);

  while (seq1.count && seq2.count)
    {
      size_t i;
      diff = keycmp (&seq1.lines[0], &seq2.lines[0]);
      if (diff < 0)
	{
	  if (print_unpairables_1)
	    prjoin (&seq1.lines[0], &uni_blank);
	  freeline (&seq1.lines[0]);
	  seq1.count = 0;
	  getseq (fp1, &seq1);
	  continue;
	}
      if (diff > 0)
	{
	  if (print_unpairables_2)
	    prjoin (&uni_blank, &seq2.lines[0]);
	  freeline (&seq2.lines[0]);
	  seq2.count = 0;
	  getseq (fp2, &seq2);
	  continue;
	}

      /* Keep reading lines from file1 as long as they continue to
         match the current line from file2.  */
      eof1 = false;
      do
	if (!getseq (fp1, &seq1))
	  {
	    eof1 = true;
	    ++seq1.count;
	    break;
	  }
      while (!keycmp (&seq1.lines[seq1.count - 1], &seq2.lines[0]));

      /* Keep reading lines from file2 as long as they continue to
         match the current line from file1.  */
      eof2 = false;
      do
	if (!getseq (fp2, &seq2))
	  {
	    eof2 = true;
	    ++seq2.count;
	    break;
	  }
      while (!keycmp (&seq1.lines[0], &seq2.lines[seq2.count - 1]));

      if (print_pairables)
	{
	  for (i = 0; i < seq1.count - 1; ++i)
	    {
	      size_t j;
	      for (j = 0; j < seq2.count - 1; ++j)
		prjoin (&seq1.lines[i], &seq2.lines[j]);
	    }
	}

      for (i = 0; i < seq1.count - 1; ++i)
	freeline (&seq1.lines[i]);
      if (!eof1)
	{
	  seq1.lines[0] = seq1.lines[seq1.count - 1];
	  seq1.count = 1;
	}
      else
	seq1.count = 0;

      for (i = 0; i < seq2.count - 1; ++i)
	freeline (&seq2.lines[i]);
      if (!eof2)
	{
	  seq2.lines[0] = seq2.lines[seq2.count - 1];
	  seq2.count = 1;
	}
      else
	seq2.count = 0;
    }

  if (print_unpairables_1 && seq1.count)
    {
      prjoin (&seq1.lines[0], &uni_blank);
      freeline (&seq1.lines[0]);
      while (get_line (fp1, &line))
	{
	  prjoin (&line, &uni_blank);
	  freeline (&line);
	}
    }

  if (print_unpairables_2 && seq2.count)
    {
      prjoin (&uni_blank, &seq2.lines[0]);
      freeline (&seq2.lines[0]);
      while (get_line (fp2, &line))
	{
	  prjoin (&uni_blank, &line);
	  freeline (&line);
	}
    }

  delseq (&seq1);
  delseq (&seq2);
}

/* Add a field spec for field FIELD of file FILE to `outlist'.  */

static void
add_field (int file, size_t field)
{
  struct outlist *o;

  assert (file == 0 || file == 1 || file == 2);
  assert (file != 0 || field == 0);

  o = xmalloc (sizeof *o);
  o->file = file;
  o->field = field;
  o->next = NULL;

  /* Add to the end of the list so the fields are in the right order.  */
  outlist_end->next = o;
  outlist_end = o;
}

/* Convert a string of decimal digits, STR (the 1-based join field number),
   to an integral value.  Upon successful conversion, return one less
   (the zero-based field number).  If it cannot be converted, give a
   diagnostic and exit.  */

static size_t
string_to_join_field (char const *str)
{
  size_t result;
  unsigned long int val;

  strtol_error s_err = xstrtoul (str, NULL, 10, &val, "");
  if (s_err == LONGINT_OVERFLOW || (s_err == LONGINT_OK && SIZE_MAX < val))
    {
      error (EXIT_FAILURE, 0,
	     _("value %s is so large that it is not representable"),
	     quote (str));
    }

  if (s_err != LONGINT_OK || val == 0)
    error (EXIT_FAILURE, 0, _("invalid field number: %s"), quote (str));

  result = val - 1;

  return result;
}

/* Convert a single field specifier string, S, to a *FILE_INDEX, *FIELD_INDEX
   pair.  In S, the field index string is 1-based; *FIELD_INDEX is zero-based.
   If S is valid, return true.  Otherwise, give a diagnostic and exit.  */

static void
decode_field_spec (const char *s, int *file_index, size_t *field_index)
{
  /* The first character must be 0, 1, or 2.  */
  switch (s[0])
    {
    case '0':
      if (s[1])
        {
	  /* `0' must be all alone -- no `.FIELD'.  */
	  error (EXIT_FAILURE, 0, _("invalid field specifier: %s"), quote (s));
	}
      *file_index = 0;
      *field_index = 0;
      break;

    case '1':
    case '2':
      if (s[1] != '.')
	error (EXIT_FAILURE, 0, _("invalid field specifier: %s"), quote (s));
      *file_index = s[0] - '0';
      *field_index = string_to_join_field (s + 2);
      break;

    default:
      error (EXIT_FAILURE, 0,
	     _("invalid file number in field spec: %s"), quote (s));
      break;
    }
}

/* Add the comma or blank separated field spec(s) in STR to `outlist'.  */

static void
add_field_list (char *str)
{
  char *p = str;

  do
    {
      int file_index;
      size_t field_index;
      char const *spec_item = p;

      p = strpbrk (p, ", \t");
      if (p)
        *p++ = '\0';
      decode_field_spec (spec_item, &file_index, &field_index);
      add_field (file_index, field_index);
    }
  while (p);
}

/* Set the join field *VAR to VAL, but report an error if *VAR is set
   more than once to incompatible values.  */

static void
set_join_field (size_t *var, size_t val)
{
  if (*var != SIZE_MAX && *var != val)
    {
      unsigned long int var1 = *var + 1;
      unsigned long int val1 = val + 1;
      error (EXIT_FAILURE, 0, _("incompatible join fields %lu, %lu"),
	     var1, val1);
    }
  *var = val;
}

/* Status of command-line arguments.  */

enum operand_status
  {
    /* This argument must be an operand, i.e., one of the files to be
       joined.  */
    MUST_BE_OPERAND,

    /* This might be the argument of the preceding -j1 or -j2 option,
       or it might be an operand.  */
    MIGHT_BE_J1_ARG,
    MIGHT_BE_J2_ARG,

    /* This might be the argument of the preceding -o option, or it might be
       an operand.  */
    MIGHT_BE_O_ARG
  };

/* Add NAME to the array of input file NAMES with operand statuses
   OPERAND_STATUS; currently there are NFILES names in the list.  */

static void
add_file_name (char *name, char *names[2],
	       int operand_status[2], int joption_count[2], int *nfiles,
	       int *prev_optc_status, int *optc_status)
{
  int n = *nfiles;

  if (n == 2)
    {
      bool op0 = (operand_status[0] == MUST_BE_OPERAND);
      char *arg = names[op0];
      switch (operand_status[op0])
	{
	case MUST_BE_OPERAND:
	  error (0, 0, _("extra operand %s"), quote (name));
	  usage (EXIT_FAILURE);

	case MIGHT_BE_J1_ARG:
	  joption_count[0]--;
	  set_join_field (&join_field_1, string_to_join_field (arg));
	  break;

	case MIGHT_BE_J2_ARG:
	  joption_count[1]--;
	  set_join_field (&join_field_2, string_to_join_field (arg));
	  break;

	case MIGHT_BE_O_ARG:
	  add_field_list (arg);
	  break;
	}
      if (!op0)
	{
	  operand_status[0] = operand_status[1];
	  names[0] = names[1];
	}
      n = 1;
    }

  operand_status[n] = *prev_optc_status;
  names[n] = name;
  *nfiles = n + 1;
  if (*prev_optc_status == MIGHT_BE_O_ARG)
    *optc_status = MIGHT_BE_O_ARG;
}

int
main (int argc, char **argv)
{
  int optc_status;
  int prev_optc_status = MUST_BE_OPERAND;
  int operand_status[2];
  int joption_count[2] = { 0, 0 };
  char *names[2];
  FILE *fp1, *fp2;
  int optc;
  int nfiles = 0;
  int i;

  initialize_main (&argc, &argv);
  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);
  hard_LC_COLLATE = hard_locale (LC_COLLATE);

  atexit (close_stdout);

  print_pairables = true;

  while ((optc = getopt_long (argc, argv, "-a:e:i1:2:j:o:t:v:",
			      longopts, NULL))
	 != -1)
    {
      optc_status = MUST_BE_OPERAND;

      switch (optc)
	{
	case 'v':
	    print_pairables = false;
	    /* Fall through.  */

	case 'a':
	  {
	    unsigned long int val;
	    if (xstrtoul (optarg, NULL, 10, &val, "") != LONGINT_OK
		|| (val != 1 && val != 2))
	      error (EXIT_FAILURE, 0,
		     _("invalid field number: %s"), quote (optarg));
	    if (val == 1)
	      print_unpairables_1 = true;
	    else
	      print_unpairables_2 = true;
	  }
	  break;

	case 'e':
	  if (empty_filler && ! STREQ (empty_filler, optarg))
	    error (EXIT_FAILURE, 0,
		   _("conflicting empty-field replacement strings"));
	  empty_filler = optarg;
	  break;

	case 'i':
	  ignore_case = true;
	  break;

	case '1':
	  set_join_field (&join_field_1, string_to_join_field (optarg));
	  break;

	case '2':
	  set_join_field (&join_field_2, string_to_join_field (optarg));
	  break;

	case 'j':
	  if ((optarg[0] == '1' || optarg[0] == '2') && !optarg[1]
	      && optarg == argv[optind - 1] + 2)
	    {
	      /* The argument was either "-j1" or "-j2".  */
	      bool is_j2 = (optarg[0] == '2');
	      joption_count[is_j2]++;
	      optc_status = MIGHT_BE_J1_ARG + is_j2;
	    }
	  else
	    {
	      set_join_field (&join_field_1, string_to_join_field (optarg));
	      set_join_field (&join_field_2, join_field_1);
	    }
	  break;

	case 'o':
	  add_field_list (optarg);
	  optc_status = MIGHT_BE_O_ARG;
	  break;

	case 't':
	  {
	    unsigned char newtab = optarg[0];
	    if (! newtab)
	      error (EXIT_FAILURE, 0, _("empty tab"));
	    if (optarg[1])
	      {
		if (STREQ (optarg, "\\0"))
		  newtab = '\0';
		else
		  error (EXIT_FAILURE, 0, _("multi-character tab `%s'"),
			 optarg);
	      }
	    if (0 <= tab && tab != newtab)
	      error (EXIT_FAILURE, 0, _("incompatible tabs"));
	    tab = newtab;
	  }
	  break;

	case 1:		/* Non-option argument.  */
	  add_file_name (optarg, names, operand_status, joption_count,
			 &nfiles, &prev_optc_status, &optc_status);
	  break;

	case_GETOPT_HELP_CHAR;

	case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);

	default:
	  usage (EXIT_FAILURE);
	}

      prev_optc_status = optc_status;
    }

  /* Process any operands after "--".  */
  prev_optc_status = MUST_BE_OPERAND;
  while (optind < argc)
    add_file_name (argv[optind++], names, operand_status, joption_count,
		   &nfiles, &prev_optc_status, &optc_status);

  if (nfiles != 2)
    {
      if (nfiles == 0)
	error (0, 0, _("missing operand"));
      else
	error (0, 0, _("missing operand after %s"), quote (argv[argc - 1]));
      usage (EXIT_FAILURE);
    }

  /* If "-j1" was specified and it turns out not to have had an argument,
     treat it as "-j 1".  Likewise for -j2.  */
  for (i = 0; i < 2; i++)
    if (joption_count[i] != 0)
      {
	set_join_field (&join_field_1, i);
	set_join_field (&join_field_2, i);
      }

  if (join_field_1 == SIZE_MAX)
    join_field_1 = 0;
  if (join_field_2 == SIZE_MAX)
    join_field_2 = 0;

  fp1 = STREQ (names[0], "-") ? stdin : fopen_safer (names[0], "r");
  if (!fp1)
    error (EXIT_FAILURE, errno, "%s", names[0]);
  fp2 = STREQ (names[1], "-") ? stdin : fopen_safer (names[1], "r");
  if (!fp2)
    error (EXIT_FAILURE, errno, "%s", names[1]);
  if (fp1 == fp2)
    error (EXIT_FAILURE, errno, _("both files cannot be standard input"));
  join (fp1, fp2);

  if (fclose (fp1) != 0)
    error (EXIT_FAILURE, errno, "%s", names[0]);
  if (fclose (fp2) != 0)
    error (EXIT_FAILURE, errno, "%s", names[1]);

  exit (EXIT_SUCCESS);
}