cat.c

ITT: make your best, most elegant implementation of cat(1) in C. Doesn't have to be POSIX compliant; for example, mine takes no option arguments because that's how I think it should be, whereas I think that POSIX specifies a few options.

#include <stdio.h>
int main(int argc, char **argv) {
    char b[4096];
    FILE *f = stdin;
    int i;
    size_t s;
    if (argc == 1)
        goto noargs;
    for (i = 1; i < argc; i++) {
        f = fopen(argv[i], "rb");
        if (!f) {
            fprintf(stderr, "%s: failed to open %s\n", argv[0], argv[i]);
            continue;
        }
        noargs:
        while ((s = fread(b, 1, 4096, f)))
            fwrite(b, 1, s, stdout);
    }
    return 0;
}

Why is this the best in my opinion? It is short, simple, fast, serves just the purpose of concatenating files and no more, and even has a clever and elegant trick to handle the special case of no arguments without code duplication.

GNU QUALITY


/* cat -- concatenate files and print on the standard output.
   Copyright (C) 1988, 1990-1991, 1995-2011 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 3 of the License, 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, see <http://www.gnu.org/licenses/>;.  */

/* Differences from the Unix cat:
   * Always unbuffered, -u is ignored.
   * Usually much faster than other versions of cat, the difference
   is especially apparent when using the -v option.

   By tege@sics.se, Torbjorn Granlund, advised by rms, Richard Stallman.  */

#include <config.h>

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

#if HAVE_STROPTS_H
# include <stropts.h>
#endif
#include <sys/ioctl.h>

#include "system.h"
#include "error.h"
#include "fadvise.h"
#include "full-write.h"
#include "quote.h"
#include "safe-read.h"
#include "xfreopen.h"

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

#define AUTHORS \
  proper_name_utf8 ("Torbjorn Granlund", "Torbj\303\266rn Granlund"), \
  proper_name ("Richard M. Stallman")

/* Name of input file.  May be "-".  */
static char const *infile;

/* Descriptor on which input file is open.  */
static int input_desc;

/* Buffer for line numbers.
   An 11 digit counter may overflow within an hour on a P2/466,
   an 18 digit counter needs about 1000y */
#define LINE_COUNTER_BUF_LEN 20
static char line_buf[LINE_COUNTER_BUF_LEN] =
  {
    ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ',
    ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', '0',
    '\t', '\0'
  };

/* Position in `line_buf' where printing starts.  This will not change
   unless the number of lines is larger than 999999.  */
static char *line_num_print = line_buf + LINE_COUNTER_BUF_LEN - 8;

/* Position of the first digit in `line_buf'.  */
static char *line_num_start = line_buf + LINE_COUNTER_BUF_LEN - 3;

/* Position of the last digit in `line_buf'.  */
static char *line_num_end = line_buf + LINE_COUNTER_BUF_LEN - 3;

/* Preserves the `cat' function's local `newlines' between invocations.  */
static int newlines2 = 0;

void
usage (int status)
{
  if (status != EXIT_SUCCESS)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
             program_name);
  else
    {
      printf (_("\
Usage: %s [OPTION]... [FILE]...\n\
"),
              program_name);
      fputs (_("\
Concatenate FILE(s), or standard input, to standard output.\n\
\n\
  -A, --show-all           equivalent to -vET\n\
  -b, --number-nonblank    number nonempty output lines, overrides -n\n\
  -e                       equivalent to -vE\n\
  -E, --show-ends          display $ at end of each line\n\
  -n, --number             number all output lines\n\
  -s, --squeeze-blank      suppress repeated empty output lines\n\
"), stdout);
      fputs (_("\
  -t                       equivalent to -vT\n\
  -T, --show-tabs          display TAB characters as ^I\n\
  -u                       (ignored)\n\
  -v, --show-nonprinting   use ^ and M- notation, except for LFD and TAB\n\
"), stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      fputs (_("\
\n\
With no FILE, or when FILE is -, read standard input.\n\
"), stdout);
      printf (_("\
\n\
Examples:\n\
  %s f - g  Output f's contents, then standard input, then g's contents.\n\
  %s        Copy standard input to standard output.\n\
"),
              program_name, program_name);
      emit_ancillary_info ();
    }
  exit (status);
}

/* Compute the next line number.  */

static void
next_line_num (void)
{
  char *endp = line_num_end;
  do
    {
      if ((*endp)++ < '9')
        return;
      *endp-- = '0';
    }
  while (endp >= line_num_start);
  if (line_num_start > line_buf)
    *--line_num_start = '1';
  else
    *line_buf = '>';
  if (line_num_start < line_num_print)
    line_num_print--;
}

/* Plain cat.  Copies the file behind `input_desc' to STDOUT_FILENO.
   Return true if successful.  */

static bool
simple_cat (
     /* Pointer to the buffer, used by reads and writes.  */
     char *buf,

     /* Number of characters preferably read or written by each read and write
        call.  */
     size_t bufsize)
{
  /* Actual number of characters read, and therefore written.  */
  size_t n_read;

  /* Loop until the end of the file.  */

  while (true)
    {
      /* Read a block of input.  */

      n_read = safe_read (input_desc, buf, bufsize);
      if (n_read == SAFE_READ_ERROR)
        {
          error (0, errno, "%s", infile);
          return false;
        }

      /* End of this file?  */

      if (n_read == 0)
        return true;

      /* Write this block out.  */

      {
        /* The following is ok, since we know that 0 < n_read.  */
        size_t n = n_read;
        if (full_write (STDOUT_FILENO, buf, n) != n)
          error (EXIT_FAILURE, errno, _("write error"));
      }
    }
}

/* Write any pending output to STDOUT_FILENO.
   Pending is defined to be the *BPOUT - OUTBUF bytes starting at OUTBUF.
   Then set *BPOUT to OUTPUT if it's not already that value.  */

static inline void
write_pending (char *outbuf, char **bpout)
{
  size_t n_write = *bpout - outbuf;
  if (0 < n_write)
    {
      if (full_write (STDOUT_FILENO, outbuf, n_write) != n_write)
        error (EXIT_FAILURE, errno, _("write error"));
      *bpout = outbuf;
    }
}

/* Cat the file behind INPUT_DESC to the file behind OUTPUT_DESC.
   Return true if successful.
   Called if any option more than -u was specified.

   A newline character is always put at the end of the buffer, to make
   an explicit test for buffer end unnecessary.  */

static bool
cat (
     /* Pointer to the beginning of the input buffer.  */
     char *inbuf,

     /* Number of characters read in each read call.  */
     size_t insize,

     /* Pointer to the beginning of the output buffer.  */
     char *outbuf,

     /* Number of characters written by each write call.  */
     size_t outsize,

     /* Variables that have values according to the specified options.  */
     bool show_nonprinting,
     bool show_tabs,
     bool number,
     bool number_nonblank,
     bool show_ends,
     bool squeeze_blank)
{
  /* Last character read from the input buffer.  */
  unsigned char ch;

  /* Pointer to the next character in the input buffer.  */
  char *bpin;

  /* Pointer to the first non-valid byte in the input buffer, i.e. the
     current end of the buffer.  */
  char *eob;

  /* Pointer to the position where the next character shall be written.  */
  char *bpout;

  /* Number of characters read by the last read call.  */
  size_t n_read;

  /* Determines how many consecutive newlines there have been in the
     input.  0 newlines makes NEWLINES -1, 1 newline makes NEWLINES 1,
     etc.  Initially 0 to indicate that we are at the beginning of a
     new line.  The "state" of the procedure is determined by
     NEWLINES.  */
  int newlines = newlines2;

#ifdef FIONREAD
  /* If nonzero, use the FIONREAD ioctl, as an optimization.
     (On Ultrix, it is not supported on NFS file systems.)  */
  bool use_fionread = true;
#endif

  /* The inbuf pointers are initialized so that BPIN > EOB, and thereby input
     is read immediately.  */

  eob = inbuf;
  bpin = eob + 1;

  bpout = outbuf;