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

Copyright (C) 1987-2010 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 trap.c

$BUILTIN trap
$FUNCTION trap_builtin
$SHORT_DOC trap [-lp] [[arg] signal_spec ...]
Trap signals and other events.

Defines and activates handlers to be run when the shell receives signals
or other conditions.

ARG is a command to be read and executed when the shell receives the
signal(s) SIGNAL_SPEC.  If ARG is absent (and a single SIGNAL_SPEC
is supplied) or `-', each specified signal is reset to its original
value.  If ARG is the null string each SIGNAL_SPEC is ignored by the
shell and by the commands it invokes.

If a SIGNAL_SPEC is EXIT (0) ARG is executed on exit from the shell.  If
a SIGNAL_SPEC is DEBUG, ARG is executed before every simple command.  If
a SIGNAL_SPEC is RETURN, ARG is executed each time a shell function or a
script run by the . or source builtins finishes executing.  A SIGNAL_SPEC
of ERR means to execute ARG each time a command's failure would cause the
shell to exit when the -e option is enabled.

If no arguments are supplied, trap prints the list of commands associated
with each signal.

Options:
  -l	print a list of signal names and their corresponding numbers
  -p	display the trap commands associated with each SIGNAL_SPEC

Each SIGNAL_SPEC is either a signal name in <signal.h> or a signal number.
Signal names are case insensitive and the SIG prefix is optional.  A
signal may be sent to the shell with "kill -signal $$".

Exit Status:
Returns success unless a SIGSPEC is invalid or an invalid option is given.
$END

#include <config.h>

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

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

#include "../shell.h"
#include "../trap.h"
#include "common.h"
#include "bashgetopt.h"

static void showtrap __P((int));
static int display_traps __P((WORD_LIST *));

/* The trap command:

   trap <arg> <signal ...>
   trap <signal ...>
   trap -l
   trap -p [sigspec ...]
   trap [--]

   Set things up so that ARG is executed when SIGNAL(s) N is recieved.
   If ARG is the empty string, then ignore the SIGNAL(s).  If there is
   no ARG, then set the trap for SIGNAL(s) to its original value.  Just
   plain "trap" means to print out the list of commands associated with
   each signal number.  Single arg of "-l" means list the signal names. */

/* Possible operations to perform on the list of signals.*/
#define SET 0			/* Set this signal to first_arg. */
#define REVERT 1		/* Revert to this signals original value. */
#define IGNORE 2		/* Ignore this signal. */

extern int posixly_correct, subshell_environment;

int
trap_builtin (list)
     WORD_LIST *list;
{
  int list_signal_names, display, result, opt;

  list_signal_names = display = 0;
  result = EXECUTION_SUCCESS;

  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "lp")) != -1)
    {
      switch (opt)
	{
	case 'l':
	  list_signal_names++;
	  break;
	case 'p':
	  display++;
	  break;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

  opt = DSIG_NOCASE|DSIG_SIGPREFIX;	/* flags for decode_signal */

  if (list_signal_names)
    return (sh_chkwrite (display_signal_list ((WORD_LIST *)NULL, 1)));
  else if (display || list == 0)
    {
      initialize_terminating_signals ();
      get_all_original_signals ();
      return (sh_chkwrite (display_traps (list)));
    }
  else
    {
      char *first_arg;
      int operation, sig, first_signal;

      operation = SET;
      first_arg = list->word->word;
      first_signal = first_arg && *first_arg && all_digits (first_arg) && signal_object_p (first_arg, opt);

      /* Backwards compatibility.  XXX - question about whether or not we
	 should throw an error if an all-digit argument doesn't correspond
	 to a valid signal number (e.g., if it's `50' on a system with only
	 32 signals).  */
      if (first_signal)
	operation = REVERT;
      /* When in posix mode, the historical behavior of looking for a
	 missing first argument is disabled.  To revert to the original
	 signal handling disposition, use `-' as the first argument. */
      else if (posixly_correct == 0 && first_arg && *first_arg &&
		(*first_arg != '-' || first_arg[1]) &&
		signal_object_p (first_arg, opt) && list->next == 0)
	operation = REVERT;
      else
	{
	  list = list->next;
	  if (list == 0)
	    {
	      builtin_usage ();
	      return (EX_USAGE);
	    }
	  else if (*first_arg == '\0')
	    operation = IGNORE;
	  else if (first_arg[0] == '-' && !first_arg[1])
	    operation = REVERT;
	}

      /* If we're in a command substitution, we haven't freed the trap strings
	 (though we reset the signal handlers).  If we're setting a trap to
	 handle a signal here, free the rest of the trap strings since they
	 don't apply any more. */
      if (subshell_environment & SUBSHELL_RESETTRAP)
	{
	  free_trap_strings ();
	  subshell_environment &= ~SUBSHELL_RESETTRAP;
	}

      while (list)
	{
	  sig = decode_signal (list->word->word, opt);

	  if (sig == NO_SIG)
	    {
	      sh_invalidsig (list->word->word);
	      result = EXECUTION_FAILURE;
	    }
	  else
	    {
	      switch (operation)
		{
		  case SET:
		    set_signal (sig, first_arg);
		    break;

		  case REVERT:
		    restore_default_signal (sig);

		    /* Signals that the shell treats specially need special
		       handling. */
		    switch (sig)
		      {
		      case SIGINT:
			/* XXX - should we do this if original disposition
			   was SIG_IGN? */
			if (interactive)
			  set_signal_handler (SIGINT, sigint_sighandler);
			else
			  set_signal_handler (SIGINT, termsig_sighandler);
			break;

		      case SIGQUIT:
			/* Always ignore SIGQUIT. */
			set_signal_handler (SIGQUIT, SIG_IGN);
			break;
		      case SIGTERM:
#if defined (JOB_CONTROL)
		      case SIGTTIN:
		      case SIGTTOU:
		      case SIGTSTP:
#endif /* JOB_CONTROL */
			if (interactive)
			  set_signal_handler (sig, SIG_IGN);
			break;
		      }
		    break;

		  case IGNORE:
		    ignore_signal (sig);
		    break;
		}
	    }
	  list = list->next;
	}
    }

  return (result);
}

static void
showtrap (i)
     int i;
{
  char *t, *p, *sn;

  p = trap_list[i];
  if (p == (char *)DEFAULT_SIG && signal_is_hard_ignored (i) == 0)
    return;
  else if (signal_is_hard_ignored (i))
    t = (char *)NULL;
  else
    t = (p == (char *)IGNORE_SIG) ? (char *)NULL : sh_single_quote (p);

  sn = signal_name (i);
  /* Make sure that signals whose names are unknown (for whatever reason)
     are printed as signal numbers. */
  if (STREQN (sn, "SIGJUNK", 7) || STREQN (sn, "unknown", 7))
    printf ("trap -- %s %d\n", t ? t : "''", i);
  else if (posixly_correct)
    {
      if (STREQN (sn, "SIG", 3))
	printf ("trap -- %s %s\n", t ? t : "''", sn+3);
      else
	printf ("trap -- %s %s\n", t ? t : "''", sn);
    }
  else
    printf ("trap -- %s %s\n", t ? t : "''", sn);

  FREE (t);
}

static int
display_traps (list)
     WORD_LIST *list;
{
  int result, i;

  if (list == 0)
    {
      for (i = 0; i < BASH_NSIG; i++)
	showtrap (i);
      return (EXECUTION_SUCCESS);
    }

  for (result = EXECUTION_SUCCESS; list; list = list->next)
    {
      i = decode_signal (list->word->word, DSIG_NOCASE|DSIG_SIGPREFIX);
      if (i == NO_SIG)
	{
	  sh_invalidsig (list->word->word);
	  result = EXECUTION_FAILURE;
	}
      else
	showtrap (i);
    }

  return (result);
}