0 - UNIX Fifth Edition

main(argc, argv)
int argc;
char *argv[];
{
	int i;

	argc--;
	for(i=1; i<=argc; i++)
		printf("%s%c", argv[i], i==argc? '\n': ' ');
}

1 - OpenBSD

/*	$OpenBSD: echo.c,v 1.7 2009/10/27 23:59:21 deraadt Exp $	*/
/*	$NetBSD: echo.c,v 1.6 1995/03/21 09:04:27 cgd Exp $	*/

/*
 * Copyright (c) 1989, 1993
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* ARGSUSED */
int
main(int argc, char *argv[])
{
	int nflag;

	/* This utility may NOT do getopt(3) option parsing. */
	if (*++argv && !strcmp(*argv, "-n")) {
		++argv;
		nflag = 1;
	}
	else
		nflag = 0;

	while (*argv) {
		(void)fputs(*argv, stdout);
		if (*++argv)
			putchar(' ');
	}
	if (!nflag)
		putchar('\n');

	return 0;
}

2 - Plan 9

#include <u.h>
#include <libc.h>

void
main(int argc, char *argv[])
{
	int nflag;
	int i, len;
	char *buf, *p;

	nflag = 0;
	if(argc > 1 && strcmp(argv[1], "-n") == 0)
		nflag = 1;

	len = 1;
	for(i = 1+nflag; i < argc; i++)
		len += strlen(argv[i])+1;

	buf = malloc(len);
	if(buf == 0)
		exits("no memory");

	p = buf;
	for(i = 1+nflag; i < argc; i++){
		strcpy(p, argv[i]);
		p += strlen(p);
		if(i < argc-1)
			*p++ = ' ';
	}
		
	if(!nflag)
		*p++ = '\n';

	if(write(1, buf, p-buf) < 0){
		fprint(2, "echo: write error: %r\n");
		exits("write error");
	}

	exits((char *)0);
}

3 - FreeBSD

/*-
 * Copyright (c) 1989, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if 0
#ifndef lint
static char const copyright[] =
"@(#) Copyright (c) 1989, 1993\n\
        The Regents of the University of California.  All rights reserved.\n";
#endif /* not lint */

#ifndef lint
static char sccsid[] = "@(#)echo.c      8.1 (Berkeley) 5/31/93";
#endif /* not lint */
#endif
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include <sys/types.h>
#include <sys/uio.h>

#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

/*
 * Report an error and exit.
 * Use it instead of err(3) to avoid linking-in stdio.
 */
static __dead2 void
errexit(const char *prog, const char *reason)
{
        char *errstr = strerror(errno);
        write(STDERR_FILENO, prog, strlen(prog));
        write(STDERR_FILENO, ": ", 2);
        write(STDERR_FILENO, reason, strlen(reason));
        write(STDERR_FILENO, ": ", 2);
        write(STDERR_FILENO, errstr, strlen(errstr));
        write(STDERR_FILENO, "\n", 1);
        exit(1);
}

int
main(int argc, char *argv[])
{
        int nflag;      /* if not set, output a trailing newline. */
        int veclen;     /* number of writev arguments. */
        struct iovec *iov, *vp; /* Elements to write, current element. */
        char space[] = " ";
        char newline[] = "\n";
        char *progname = argv[0];

        /* This utility may NOT do getopt(3) option parsing. */
        if (*++argv && !strcmp(*argv, "-n")) {
                ++argv;
                --argc;
                nflag = 1;
        } else
                nflag = 0;

        veclen = (argc >= 2) ? (argc - 2) * 2 + 1 : 0;

        if ((vp = iov = malloc((veclen + 1) * sizeof(struct iovec))) == NULL)
                errexit(progname, "malloc");

        while (argv[0] != NULL) {
                size_t len;

                len = strlen(argv[0]);

                /*
                 * If the next argument is NULL then this is this
                 * the last argument, therefore we need to check
                 * for a trailing \c.
                 */
                if (argv[1] == NULL) {
                        /* is there room for a '\c' and is there one? */
                        if (len >= 2 &&
                            argv[0][len - 2] == '\\' &&
                            argv[0][len - 1] == 'c') {
                                /* chop it and set the no-newline flag. */
                                len -= 2;
                                nflag = 1;
                        }
                }
                vp->iov_base = *argv;
                vp++->iov_len = len;
                if (*++argv) {
                        vp->iov_base = space;
                        vp++->iov_len = 1;
                }
        }
        if (!nflag) {
                veclen++;
                vp->iov_base = newline;
                vp++->iov_len = 1;
        }
        /* assert(veclen == (vp - iov)); */
        while (veclen) {
                int nwrite;

                nwrite = (veclen > IOV_MAX) ? IOV_MAX : veclen;
                if (writev(STDOUT_FILENO, iov, nwrite) == -1)
                        errexit(progname, "write");
                iov += nwrite;
                veclen -= nwrite;
        }
        return 0;
}

4 - GNU coreutils

/* echo.c, derived from code echo.c in Bash.
   Copyright (C) 1987, 1989, 1991-1997, 1999-2005, 2007-2011 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/>.  */

#include <config.h>
#include <stdio.h>
#include <sys/types.h>
#include "system.h"

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

#define AUTHORS \
  proper_name ("Brian Fox"), \
  proper_name ("Chet Ramey")

/* If true, interpret backslash escapes by default.  */
#ifndef DEFAULT_ECHO_TO_XPG
enum { DEFAULT_ECHO_TO_XPG = false };
#endif

void
usage (int status)
{
  if (status != EXIT_SUCCESS)
    fprintf (stderr, _("Try `%s --help' for more information.\n"),
             program_name);
  else
    {
      printf (_("\
Usage: %s [SHORT-OPTION]... [STRING]...\n\
  or:  %s LONG-OPTION\n\
"), program_name, program_name);
      fputs (_("\
Echo the STRING(s) to standard output.\n\
\n\
  -n             do not output the trailing newline\n\
"), stdout);
      fputs (_(DEFAULT_ECHO_TO_XPG
               ? N_("\
  -e             enable interpretation of backslash escapes (default)\n\
  -E             disable interpretation of backslash escapes\n")
               : N_("\
  -e             enable interpretation of backslash escapes\n\
  -E             disable interpretation of backslash escapes (default)\n")),
             stdout);
      fputs (HELP_OPTION_DESCRIPTION, stdout);
      fputs (VERSION_OPTION_DESCRIPTION, stdout);
      fputs (_("\
\n\
If -e is in effect, the following sequences are recognized:\n\
\n\
"), stdout);
      fputs (_("\
  \\\\      backslash\n\
  \\a      alert (BEL)\n\
  \\b      backspace\n\
  \\c      produce no further output\n\
  \\e      escape\n\
  \\f      form feed\n\
  \\n      new line\n\
  \\r      carriage return\n\
  \\t      horizontal tab\n\
  \\v      vertical tab\n\
"), stdout);
      fputs (_("\
  \\0NNN   byte with octal value NNN (1 to 3 digits)\n\
  \\xHH    byte with hexadecimal value HH (1 to 2 digits)\n\
"), stdout);
      printf (USAGE_BUILTIN_WARNING, PROGRAM_NAME);
      emit_ancillary_info ();
    }
  exit (status);
}

/* Convert C from hexadecimal character to integer.  */
static int
hextobin (unsigned char c)
{
  switch (c)
    {
    default: return c - '0';
    case 'a': case 'A': return 10;
    case 'b': case 'B': return 11;
    case 'c': case 'C': return 12;
    case 'd': case 'D': return 13;
    case 'e': case 'E': return 14;
    case 'f': case 'F': return 15;
    }
}

/* Print the words in LIST to standard output.  If the first word is
   `-n', then don't print a trailing newline.  We also support the
   echo syntax from Version 9 unix systems. */

int
main (int argc, char **argv)
{
  bool display_return = true;
  bool allow_options =
    (! getenv ("POSIXLY_CORRECT")
     || (! DEFAULT_ECHO_TO_XPG && 1 < argc && STREQ (argv[1], "-n")));

  /* System V machines already have a /bin/sh with a v9 behavior.
     Use the identical behavior for these machines so that the
     existing system shell scripts won't barf.  */
  bool do_v9 = DEFAULT_ECHO_TO_XPG;

  initialize_main (&argc, &argv);
  set_program_name (argv[0]);
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);

  atexit (close_stdout);

  /* We directly parse options, rather than use parse_long_options, in
     order to avoid accepting abbreviations.  */
  if (allow_options && argc == 2)
    {
      if (STREQ (argv[1], "--help"))
        usage (EXIT_SUCCESS);

      if (STREQ (argv[1], "--version"))
        {
          version_etc (stdout, PROGRAM_NAME, PACKAGE_NAME, Version, AUTHORS,
                       (char *) NULL);
          exit (EXIT_SUCCESS);
        }
    }

  --argc;
  ++argv;

  if (allow_options)
    while (argc > 0 && *argv[0] == '-')
      {
        char const *temp = argv[0] + 1;
        size_t i;

        /* If it appears that we are handling options, then make sure that
           all of the options specified are actually valid.  Otherwise, the
           string should just be echoed.  */

        for (i = 0; temp[i]; i++)
          switch (temp[i])
            {
            case 'e': case 'E': case 'n':
              break;
            default:
              goto just_echo;
            }

        if (i == 0)
          goto just_echo;

        /* All of the options in TEMP are valid options to ECHO.
           Handle them. */
        while (*temp)
          switch (*temp++)
            {
            case 'e':
              do_v9 = true;
              break;

            case 'E':
              do_v9 = false;
              break;

            case 'n':
              display_return = false;
              break;
            }

        argc--;
        argv++;
      }

just_echo:

  if (do_v9)
    {
      while (argc > 0)
        {
          char const *s = argv[0];
          unsigned char c;

          while ((c = *s++))
            {
              if (c == '\\' && *s)
                {
                  switch (c = *s++)
                    {
                    case 'a': c = '\a'; break;
                    case 'b': c = '\b'; break;
                    case 'c': exit (EXIT_SUCCESS);
                    case 'e': c = '\x1B'; break;
                    case 'f': c = '\f'; break;
                    case 'n': c = '\n'; break;
                    case 'r': c = '\r'; break;
                    case 't': c = '\t'; break;
                    case 'v': c = '\v'; break;
                    case 'x':
                      {
                        unsigned char ch = *s;
                        if (! isxdigit (ch))
                          goto not_an_escape;
                        s++;
                        c = hextobin (ch);
                        ch = *s;
                        if (isxdigit (ch))
                          {
                            s++;
                            c = c * 16 + hextobin (ch);
                          }
                      }
                      break;
                    case '0':
                      c = 0;
                      if (! ('0' <= *s && *s <= '7'))
                        break;
                      c = *s++;
                      /* Fall through.  */
                    case '1': case '2': case '3':
                    case '4': case '5': case '6': case '7':
                      c -= '0';
                      if ('0' <= *s && *s <= '7')
                        c = c * 8 + (*s++ - '0');
                      if ('0' <= *s && *s <= '7')
                        c = c * 8 + (*s++ - '0');
                      break;
                    case '\\': break;

                    not_an_escape:
                    default:  putchar ('\\'); break;
                    }
                }
              putchar (c);
            }
          argc--;
          argv++;
          if (argc > 0)
            putchar (' ');
        }
    }
  else
    {
      while (argc > 0)
        {
          fputs (argv[0], stdout);
          argc--;
          argv++;
          if (argc > 0)
            putchar (' ');
        }
    }

  if (display_return)
    putchar ('\n');
  exit (EXIT_SUCCESS);
}