bash/builtins/trap.def

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

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$PRODUCES trap.c

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

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

ACTION is a command to be read and executed when the shell receives the
signal(s) SIGNAL_SPEC.  If ACTION is absent (and a single SIGNAL_SPEC
is supplied) or `-', each specified signal is reset to its original
value.  If ACTION 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) ACTION is executed on exit from the shell.
If a SIGNAL_SPEC is DEBUG, ACTION is executed before every simple command
and selected other commands. If a SIGNAL_SPEC is RETURN, ACTION 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 ACTION
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 trapped signal in a form that may be reused as shell input to
restore the same signal dispositions.

Options:
  -l	print a list of signal names and their corresponding numbers
  -p	display the trap commands associated with each SIGNAL_SPEC in a
		form that may be reused as shell input; or for all trapped
		signals if no arguments are supplied
  -P	display the trap commands associated with each SIGNAL_SPEC. At least
		one SIGNAL_SPEC must be supplied. -P and -p cannot be used
		together.

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 (int, int);
static int display_traps (WORD_LIST *, int);

/* The trap command:

   trap <action> <sigspec ...>
   trap <signum ...>
   trap -l
   trap -p [sigspec ...]
   trap [--]

   Set things up so that ARG is executed when SIGNAL(s) N is received.
   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. */

/* Flags saying how to display the trap list. */
#define DISP_TRAPCMD	1
#define DISP_ALLSIGS	2
#define DISP_ACTIONONLY	4

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

  list_signal_names = dflags = 0;
  result = EXECUTION_SUCCESS;

  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "lpP")) != -1)
    {
      switch (opt)
	{
	case 'l':
	  list_signal_names++;
	  break;
	case 'p':
	  dflags |= DISP_TRAPCMD;
	  break;
	case 'P':
	  dflags |= DISP_ACTIONONLY;
	  break;
	CASE_HELPOPT;
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

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

  if ((dflags & DISP_TRAPCMD) && (dflags & DISP_ACTIONONLY))
    {
      builtin_error ("cannot specify both -p and -P");
      return EX_USAGE;
    }
  if ((dflags & DISP_ACTIONONLY) && list == 0)
    {
      builtin_error ("-P requires at least one signal name");
      return EX_USAGE;
    }

  if (list_signal_names)
    return (sh_chkwrite (display_signal_list ((WORD_LIST *)NULL, 1)));
  else if (dflags || list == 0)
    {
      initialize_terminating_signals ();
      get_all_original_signals ();
      if (dflags & DISP_TRAPCMD)
	dflags |= posixly_correct ? DISP_ALLSIGS : 0;
      return (sh_chkwrite (display_traps (list, dflags)));
    }
  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? Yes, because setup_async_signals can
			   set the original disposition to SIG_IGN to keep
			   restore_signal from restoring the SIGINT
			   disposition from when the shell was invoked, and
			   we want to allow an asynchronous subshell to
			   use `trap' to restore the default disposition or
			   set a trap command. */
			if (interactive)
			  set_signal_handler (SIGINT, sigint_sighandler);
			/* special cases for interactive == 0 */
			else if (interactive_shell && (sourcelevel||running_trap||parse_and_execute_level))
			  set_signal_handler (SIGINT, sigint_sighandler);
			else
			  set_signal_handler (SIGINT, termsig_sighandler);
			break;

		      case SIGQUIT:
			/* Always ignore SIGQUIT, but allow a posix-mode shell
			   that is running asynchronously and has ignored
			   SIGQUIT to reset it to the default. POSIX interp 751. */
			if (posixly_correct && signal_is_async_ignored (SIGQUIT))
			  set_signal_handler (SIGQUIT, termsig_sighandler);
			else
			  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 (int i, int show_default)
{
  char *t, *p, *sn;
  int free_t;

  free_t = 1;
  p = trap_list[i];
  if (p == (char *)DEFAULT_SIG && signal_is_hard_ignored (i) == 0)
    {
      if (show_default)
	t = "-";
      else
	return;
      free_t = 0;
    }
  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);

  if (free_t)
    FREE (t);
}

/* Flags saying how to display the trap list. */
#define DISP_TRAPCMD    1
#define DISP_ALLSIGS    2
#define DISP_ACTIONONLY 4


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

  show_all = flags & DISP_ALLSIGS;
  if (list == 0)
    {
      for (i = 0; i < BASH_NSIG; i++)
	showtrap (i, show_all);
      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 if (flags & DISP_ACTIONONLY)
	{
	  char *t;
	  t = trap_list[i];
	  if (t == (char *)DEFAULT_SIG || signal_is_hard_ignored (i))
	    continue;
	  else if (t == (char *)IGNORE_SIG)
	    t = "";
	  printf ("%s\n", t);
	}
      else
	showtrap (i, show_all);
    }

  return (result);
}