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

Copyright (C) 1987-2021 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 exec.c

$BUILTIN exec
$FUNCTION exec_builtin
$SHORT_DOC exec [-cl] [-a name] [command [argument ...]] [redirection ...]
Replace the shell with the given command.

Execute COMMAND, replacing this shell with the specified program.
ARGUMENTS become the arguments to COMMAND.  If COMMAND is not specified,
any redirections take effect in the current shell.

Options:
  -a name	pass NAME as the zeroth argument to COMMAND
  -c	execute COMMAND with an empty environment
  -l	place a dash in the zeroth argument to COMMAND

If the command cannot be executed, a non-interactive shell exits, unless
the shell option `execfail' is set.

Exit Status:
Returns success unless COMMAND is not found or a redirection error occurs.
$END

#include <config.h>

#include "../bashtypes.h"
#include "posixstat.h"
#include <signal.h>
#include <errno.h>

#if defined (HAVE_UNISTD_H)
#  include <unistd.h>
#endif

#include <stdio.h>

#include "../bashansi.h"
#include "../bashintl.h"

#include "../shell.h"
#include "../execute_cmd.h"
#include "../findcmd.h"
#if defined (JOB_CONTROL)
#  include "../jobs.h"
#endif
#include "../flags.h"
#include "../trap.h"
#if defined (HISTORY)
#  include "../bashhist.h"
#endif
#include "common.h"
#include "bashgetopt.h"
#include "input.h"

/* Not all systems declare ERRNO in errno.h... and some systems #define it! */
#if !defined (errno)
extern int errno;
#endif /* !errno */

extern REDIRECT *redirection_undo_list;
extern char *exec_argv0;

int no_exit_on_failed_exec;

/* If the user wants this to look like a login shell, then
   prepend a `-' onto NAME and return the new name. */
static char *
mkdashname (name)
     char *name;
{
  char *ret;

  ret = (char *)xmalloc (2 + strlen (name));
  ret[0] = '-';
  strcpy (ret + 1, name);
  return ret;
}

int
exec_builtin (list)
     WORD_LIST *list;
{
  int exit_value = EXECUTION_FAILURE;
  int cleanenv, login, opt, orig_job_control;
  char *argv0, *command, **args, **env, *newname, *com2;

  cleanenv = login = orig_job_control = 0;
  exec_argv0 = argv0 = (char *)NULL;

  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "cla:")) != -1)
    {
      switch (opt)
	{
	case 'c':
	  cleanenv = 1;
	  break;
	case 'l':
	  login = 1;
	  break;
	case 'a':
	  argv0 = list_optarg;
	  break;
	CASE_HELPOPT;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

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

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

#if defined (RESTRICTED_SHELL)
  if (restricted)
    {
      sh_restricted ((char *)NULL);
      return (EXECUTION_FAILURE);
    }
#endif /* RESTRICTED_SHELL */

  args = strvec_from_word_list (list, 1, 0, (int *)NULL);
  env = (char **)0;

  /* A command with a slash anywhere in its name is not looked up in $PATH. */
  command = absolute_program (args[0]) ? args[0] : search_for_command (args[0], 1);

  if (command == 0)
    {
      if (file_isdir (args[0]))
	{
#if defined (EISDIR)
	  builtin_error (_("%s: cannot execute: %s"), args[0], strerror (EISDIR));
#else
	  builtin_error (_("%s: cannot execute: %s"), args[0], strerror (errno));
#endif
	  exit_value = EX_NOEXEC;
	}
      else
	{
	  sh_notfound (args[0]);
	  exit_value = EX_NOTFOUND;	/* As per Posix.2, 3.14.6 */
	}
      goto failed_exec;
    }

  com2 = full_pathname (command);
  if (com2)
    {
      if (command != args[0])
	free (command);
      command = com2;
    }

  if (argv0)
    {
      free (args[0]);
      args[0] = login ? mkdashname (argv0) : savestring (argv0);
      exec_argv0 = savestring (args[0]);
    }
  else if (login)
    {
      newname = mkdashname (args[0]);
      free (args[0]);
      args[0] = newname;
    }

  /* 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.  If we've already forked
     and are in a subshell, we don't want to decrement the shell level,
     since we are `increasing' the level */

  if (cleanenv == 0 && (subshell_environment & SUBSHELL_PAREN) == 0)
    adjust_shell_level (-1);

  if (cleanenv)
    {
      env = strvec_create (1);
      env[0] = (char *)0;
    }
  else
    {	
      maybe_make_export_env ();
      env = export_env;
    }

#if defined (HISTORY)
  if (interactive_shell && subshell_environment == 0)
    maybe_save_shell_history ();
#endif /* HISTORY */

  reset_signal_handlers ();		/* leave trap strings in place */

#if defined (JOB_CONTROL)
  orig_job_control = job_control;	/* XXX - was also interactive_shell */
  if (subshell_environment == 0)
    end_job_control ();
  if (interactive || job_control)
    default_tty_job_signals ();		/* undo initialize_job_signals */
#endif /* JOB_CONTROL */

#if defined (BUFFERED_INPUT)
  if (default_buffered_input >= 0)
    sync_buffered_stream (default_buffered_input);
#endif

  exit_value = shell_execve (command, args, env);

  /* We have to set this to NULL because shell_execve has called realloc()
     to stuff more items at the front of the array, which may have caused
     the memory to be freed by realloc().  We don't want to free it twice. */
  args = (char **)NULL;
  if (cleanenv == 0)
    adjust_shell_level (1);

  if (exit_value == EX_NOTFOUND)	/* no duplicate error message */
    goto failed_exec;
  else if (executable_file (command) == 0)
    {
      builtin_error (_("%s: cannot execute: %s"), command, strerror (errno));
      exit_value = EX_NOEXEC;	/* As per Posix.2, 3.14.6 */
    }
  else
    file_error (command);

failed_exec:
  FREE (command);

  if (subshell_environment || (interactive == 0 && no_exit_on_failed_exec == 0))
    exit_shell (last_command_exit_value = exit_value);

  if (args)
    strvec_dispose (args);

  if (env && env != export_env)
    strvec_dispose (env);

  /* If we're not exiting after the exec fails, we restore the shell signal
     handlers and then modify the signal dispositions based on the trap strings
     before the failed exec. */
  initialize_signals (1);
  restore_traps ();

#if defined (JOB_CONTROL)
  if (orig_job_control)
    restart_job_control ();
#endif /* JOB_CONTROL */

  return (exit_value);
}