source: vendor/bash/3.1-p17/examples/loadables/push.c

/*
 * push - anyone remember TOPS-20?
 *
 */

#include <config.h>
#include <stdio.h>
#include <errno.h>

#include "builtins.h"
#include "shell.h"
#include "jobs.h"
#include "bashgetopt.h"

#ifndef errno
extern int errno;
#endif

extern int dollar_dollar_pid;
extern int last_command_exit_value;

int
push_builtin (list)
     WORD_LIST *list;
{
  pid_t pid;
  int xstatus, opt;

  xstatus = EXECUTION_SUCCESS;
  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "")) != -1)
    {
      switch (opt)
        {
        default:
          builtin_usage ();
          return (EX_USAGE);
        }
    }
  list = loptend;  

  pid = make_child (savestring ("push"), 0);
  if (pid == -1)
    {
      builtin_error ("cannot fork: %s", strerror (errno));
      return (EXECUTION_FAILURE);
    }
  else if (pid == 0)
    {
      /* Shell variable adjustments: $SHLVL, $$, $PPID, $! */
      adjust_shell_level (1);
      dollar_dollar_pid = getpid ();
      set_ppid ();

      /* Clean up job control stuff. */
      stop_making_children ();
      cleanup_the_pipeline ();
      delete_all_jobs (0);

      last_asynchronous_pid = NO_PID;

      /* Make sure the job control code has the right values for
         the shell's process group and tty process group, and that
         the signals are set correctly for job control. */
      initialize_job_control (0);
      initialize_job_signals ();

      /* And read commands until exit. */
      reader_loop ();
      exit_shell (last_command_exit_value);
    }
  else
    {
      stop_pipeline (0, (COMMAND *)NULL);
      xstatus = wait_for (pid);
      return (xstatus);
    }   
}

char *push_doc[] = {
        "Create a child that is an exact duplicate of the running shell",
        "and wait for it to exit.  The $SHLVL, $!, $$, and $PPID variables",
        "are adjusted in the child.  The return value is the exit status",
        "of the child.",
        (char *)NULL
};

struct builtin push_struct = {
        "push",
        push_builtin,
        BUILTIN_ENABLED,
        push_doc,
        "push",
        0
};