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

Copyright (C) 1987, 1989, 1991 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 1, 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; see the file COPYING.  If not, write to the Free Software
Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

$PRODUCES exec.c

$BUILTIN exec
$FUNCTION exec_builtin
$SHORT_DOC exec [ [-] file [redirection ...]]
Exec FILE, replacing this shell with the specified program.
If FILE is not specified, the redirections take effect in this
shell.  If the first argument is `-', then place a dash in the
zeroth arg passed to FILE.  This is what login does.  If the file
cannot be exec'ed for some reason, the shell exits, unless the
shell variable "no_exit_on_failed_exec" exists.
$END

#include "../shell.h"
#include <signal.h>
#include <errno.h>

extern int interactive, errno;
extern REDIRECT *redirection_undo_list;

int
exec_builtin (list)
     WORD_LIST *list;
{
  extern char *find_user_command ();

  maybe_make_export_env ();

  /* First, let the redirections remain. */
  dispose_redirects (redirection_undo_list);
  redirection_undo_list = (REDIRECT *)NULL;

  if (!list)
    return (EXECUTION_SUCCESS);
  else
    {
      /* Otherwise, execve the new command with args. */
      char *command, **args;
      int dash_name = 0;

      if (strcmp (list->word->word, "-") == 0)
	{
	  /* The user would like to exec this command as if it was a
	     login command.  Do so. */
	  list = list->next;
	  dash_name++;
	}

      if (!list)
	return (EXECUTION_SUCCESS);

      args = (char **)make_word_array (list);

      /* A command with a slash anywhere in its name is not looked up in
	 the search path. */
      if (absolute_program (args[0]))
	command = args[0];
      else
	command = find_user_command (args[0]);
      if (!command)
	{
	  builtin_error ("%s: not found", args[0]);
	  goto failed_exec;
	}

      command = (char *)full_pathname (command);
      /* If the user wants this to look like a login shell, then
	 prepend a `-' onto the first argument (argv[0]). */
      if (dash_name)
	{
	  char *new_name = (char *)xmalloc (2 + strlen (args[0]));
	  strcpy (new_name, "-");
	  strcat (new_name, args[0]);
	  free (args[0]);
	  args[0] = new_name;
	}

      /* Decrement SHLVL by 1 so a new shell started here has the same value,
	 preserving the appearance.  After we do that, we need to change the
	 exported environment to include the new value. */
      adjust_shell_level (-1);
      maybe_make_export_env ();

      maybe_save_shell_history ();

      restore_default_signal (SIGINT);
      restore_default_signal (SIGQUIT);
      restore_default_signal (SIGTERM);
      restore_original_signals ();

      shell_execve (command, args, export_env);

      adjust_shell_level (1);

      if (!executable_file (command))
	builtin_error ("%s: cannot execute: %s", command, strerror (errno));
      else
	file_error (command);

  failed_exec:
      if (!interactive && !find_variable ("no_exit_on_failed_exec"))
	exit (EXECUTION_FAILURE);
      return (EXECUTION_FAILURE);
    }
}
