This file is command.def, from which is created command.c.
It implements the builtin "command" in Bash.

Copyright (C) 1987-2009 Free Software Foundation, Inc.

This file is part of GNU Bash, the Bourne Again SHell.

Bash 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.

Bash 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 Bash.  If not, see <http://www.gnu.org/licenses/>.

$PRODUCES command.c

$BUILTIN command
$FUNCTION command_builtin
$SHORT_DOC command [-pVv] command [arg ...]
Execute a simple command or display information about commands.

Runs COMMAND with ARGS suppressing  shell function lookup, or display
information about the specified COMMANDs.  Can be used to invoke commands
on disk when a function with the same name exists.

Options:
  -p	use a default value for PATH that is guaranteed to find all of
	the standard utilities
  -v	print a description of COMMAND similar to the `type' builtin
  -V	print a more verbose description of each COMMAND

Exit Status:
Returns exit status of COMMAND, or failure if COMMAND is not found.
$END

#include <config.h>

#if defined (HAVE_UNISTD_H)
#  ifdef _MINIX
#    include <sys/types.h>
#  endif
#  include <unistd.h>
#endif

#include "../bashansi.h"

#include "../shell.h"
#include "../execute_cmd.h"
#include "../flags.h"
#include "bashgetopt.h"
#include "common.h"

#if defined (_CS_PATH) && defined (HAVE_CONFSTR) && !HAVE_DECL_CONFSTR
extern size_t confstr __P((int, char *, size_t));
#endif

extern int subshell_environment;

static void restore_path __P((char *));
static char *get_standard_path __P((void));

/* Run the commands mentioned in LIST without paying attention to shell
   functions. */
int
command_builtin (list)
     WORD_LIST *list;
{
  int result, verbose, use_standard_path, opt;
  char *old_path, *standard_path;
  COMMAND *command;

  verbose = use_standard_path = 0;
  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "pvV")) != -1)
    {
      switch (opt)
	{
	case 'p':
	  use_standard_path = 1;
	  break;
	case 'V':
	  verbose = CDESC_SHORTDESC|CDESC_ABSPATH;	/* look in common.h for constants */
	  break;
	case 'v':
	  verbose = CDESC_REUSABLE;	/* ditto */
	  break;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

  if (list == 0)
    return (EXECUTION_SUCCESS);

#if defined (RESTRICTED_SHELL)
  if (use_standard_path && restricted)
    {
      sh_restricted ("-p");
      return (EXECUTION_FAILURE);
    }
#endif

  begin_unwind_frame ("command_builtin");

  if (use_standard_path)
    {      
      old_path = get_string_value ("PATH");
      /* If old_path is NULL, $PATH is unset.  If so, we want to make sure
	 it's unset after this command completes. */
      if (old_path)
	old_path = savestring (old_path);
      add_unwind_protect ((Function *)restore_path, old_path);

      standard_path = get_standard_path ();
      bind_variable ("PATH", standard_path ? standard_path : "", 0);
      stupidly_hack_special_variables ("PATH");
      FREE (standard_path);
    }

  if (verbose)
    {
      int found, any_found;

      for (any_found = 0; list; list = list->next)
	{
	  found = describe_command (list->word->word, verbose);

	  if (found == 0 && verbose != CDESC_REUSABLE)
	    sh_notfound (list->word->word);

	  any_found += found;
	}

      run_unwind_frame ("command_builtin");
      return (any_found ? EXECUTION_SUCCESS : EXECUTION_FAILURE);
    }

#define COMMAND_BUILTIN_FLAGS (CMD_NO_FUNCTIONS | CMD_INHIBIT_EXPANSION | CMD_COMMAND_BUILTIN)

  /* We don't want this to be reparsed (consider command echo 'foo &'), so
     just make a simple_command structure and call execute_command with it. */
  command = make_bare_simple_command ();
  command->value.Simple->words = (WORD_LIST *)copy_word_list (list);
  command->value.Simple->redirects = (REDIRECT *)NULL;
  command->flags |= COMMAND_BUILTIN_FLAGS;
  command->value.Simple->flags |= COMMAND_BUILTIN_FLAGS;
#if 0
  /* This breaks for things like ( cd /tmp ; command z ababa ; echo next )
     or $(command echo a ; command echo b;) or even
     { command echo a; command echo b; } & */
  /* If we're in a subshell, see if we can get away without forking
     again, since we've already forked to run this builtin. */
  if (subshell_environment)
    {
      command->flags |= CMD_NO_FORK;
      command->value.Simple->flags |= CMD_NO_FORK;
    }
#endif
  add_unwind_protect ((char *)dispose_command, command);
  result = execute_command (command);

  run_unwind_frame ("command_builtin");

  return (result);
}

/* Restore the value of the $PATH variable after replacing it when
   executing `command -p'. */
static void
restore_path (var)
     char *var;
{
  if (var)
    {
      bind_variable ("PATH", var, 0);
      free (var);
    }
  else
    unbind_variable ("PATH");

  stupidly_hack_special_variables ("PATH");
}

/* Return a value for PATH that is guaranteed to find all of the standard
   utilities.  This uses Posix.2 configuration variables, if present.  It
   uses a value defined in config.h as a last resort. */
static char *
get_standard_path ()
{
#if defined (_CS_PATH) && defined (HAVE_CONFSTR)
  char *p;
  size_t len;

  len = (size_t)confstr (_CS_PATH, (char *)NULL, (size_t)0);
  if (len > 0)
    {
      p = (char *)xmalloc (len + 2);
      *p = '\0';
      confstr (_CS_PATH, p, len);
      return (p);
    }
  else
    return (savestring (STANDARD_UTILS_PATH));
#else /* !_CS_PATH || !HAVE_CONFSTR  */
#  if defined (CS_PATH)
  return (savestring (CS_PATH));
#  else
  return (savestring (STANDARD_UTILS_PATH));
#  endif /* !CS_PATH */
#endif /* !_CS_PATH || !HAVE_CONFSTR */
}