This file is fg_bg.def, from which is created fg_bg.c.
It implements the builtins "bg" and "fg" in Bash.

Copyright (C) 1987-2020 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 fg_bg.c

$BUILTIN fg
$FUNCTION fg_builtin
$DEPENDS_ON JOB_CONTROL
$SHORT_DOC fg [job_spec]
Move job to the foreground.

Place the job identified by JOB_SPEC in the foreground, making it the
current job.  If JOB_SPEC is not present, the shell's notion of the
current job is used.

Exit Status:
Status of command placed in foreground, or failure if an error occurs.
$END

#include <config.h>

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

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

#include "../bashintl.h"

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

#if defined (JOB_CONTROL)
static int fg_bg PARAMS((WORD_LIST *, int));

/* How to bring a job into the foreground. */
int
fg_builtin (list)
     WORD_LIST *list;
{
  int fg_bit;
  register WORD_LIST *t;

  CHECK_HELPOPT (list);

  if (job_control == 0)
    {
      sh_nojobs ((char *)NULL);
      return (EXECUTION_FAILURE);
    }

  if (no_options (list))
    return (EX_USAGE);
  list = loptend;

  /* If the last arg on the line is '&', then start this job in the
     background.  Else, fg the job. */
  for (t = list; t && t->next; t = t->next)
    ;
  fg_bit = (t && t->word->word[0] == '&' && t->word->word[1] == '\0') == 0;

  return (fg_bg (list, fg_bit));
}
#endif /* JOB_CONTROL */

$BUILTIN bg
$FUNCTION bg_builtin
$DEPENDS_ON JOB_CONTROL
$SHORT_DOC bg [job_spec ...]
Move jobs to the background.

Place the jobs identified by each JOB_SPEC in the background, as if they
had been started with `&'.  If JOB_SPEC is not present, the shell's notion
of the current job is used.

Exit Status:
Returns success unless job control is not enabled or an error occurs.
$END

#if defined (JOB_CONTROL)
/* How to put a job into the background. */
int
bg_builtin (list)
     WORD_LIST *list;
{
  int r;

  CHECK_HELPOPT (list);

  if (job_control == 0)
    {
      sh_nojobs ((char *)NULL);
      return (EXECUTION_FAILURE);
    }

  if (no_options (list))
    return (EX_USAGE);
  list = loptend;

  /* This relies on the fact that fg_bg() takes a WORD_LIST *, but only acts
     on the first member (if any) of that list. */
  r = EXECUTION_SUCCESS;
  do
    {
      if (fg_bg (list, 0) == EXECUTION_FAILURE)
	r = EXECUTION_FAILURE;
      if (list)
	list = list->next;
    }
  while (list);

  return r;
}

/* How to put a job into the foreground/background. */
static int
fg_bg (list, foreground)
     WORD_LIST *list;
     int foreground;
{
  sigset_t set, oset;
  int job, status, old_async_pid;
  JOB *j;

  BLOCK_CHILD (set, oset);
  job = get_job_spec (list);

  if (INVALID_JOB (job))
    {
      if (job != DUP_JOB)
	sh_badjob (list ? list->word->word : _("current"));

      goto failure;
    }

  j = get_job_by_jid (job);
  /* Or if j->pgrp == shell_pgrp. */
  if (IS_JOBCONTROL (job) == 0)
    {
      builtin_error (_("job %d started without job control"), job + 1);
      goto failure;
    }

  if (foreground == 0)
    {
      old_async_pid = last_asynchronous_pid;
      last_asynchronous_pid = j->pgrp;	/* As per Posix.2 5.4.2 */
    }

  status = start_job (job, foreground);

  if (status >= 0)
    {
    /* win: */
      UNBLOCK_CHILD (oset);
      return (foreground ? status : EXECUTION_SUCCESS);
    }
  else
    {
      if (foreground == 0)
	last_asynchronous_pid = old_async_pid;

    failure:
      UNBLOCK_CHILD (oset);
      return (EXECUTION_FAILURE);
    }
}
#endif /* JOB_CONTROL */