Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mailrus!cwjcc!kiwi!chet
From: chet@kiwi.CWRU.EDU (Chet Ramey)
Newsgroups: gnu.bash.bug
Subject: Re: return values of the function and pipe
Summary: return 0 from function will never work in vanilla bash 1.02,
	 but I think I have a fix
Message-ID: <420@cwjcc.CWRU.Edu>
Date: 12 Jul 89 22:05:35 GMT
References: <8907111627.AA08421@vlsi.caltech.edu>
Sender: news@cwjcc.CWRU.Edu
Reply-To: chet@kiwi.INS.CWRU.Edu (Chet Ramey)
Distribution: gnu
Organization: CWRU Andrew R. Jennings Computing Center
Lines: 107

In article <8907111627.AA08421@vlsi.caltech.edu> drazen@VLSI.CALTECH.EDU (Drazen Borkovic) writes:
>There are 2 problems:
>1. Return  from a function doesn't work correctly. 

You're right, but I could not reproduce this exactly on a Sun-3 (SunOS
3.5), an IBM RT (4.3BSD), or a Vax (Ultrix 3.0).  I never got the "can only
`return' from a function" error you saw. 

>   Value  returned from the function is not correct.

THIS CANNOT BE FIXED WITHOUT A REDESIGN (or at least a rethinking) OF THE
FUNCTION EXECUTION MECHANISM.  bash 1.02 relies on the property of longjmp
that lets you specify what value the corresponding setjmp call will return
when you call it.  YOU CANNOT PORTABLY SPECIFY 0 HERE.  Most longjmps that
I know of (Sun, Ultrix) will change a 0 value to a 1, since setjmp will
only return 0 the first time it is called.  On 4.3 BSD, it appears that you
can make setjmp return 0 by specifying 0 to longjmp, but that just makes
bash recurse infinitely in execute_simple_command(). 

I just tried the YAGV (`Yet Another Global Variable') approach to fixing this,
and it seems to work (at least for a variant of your pushd example) on the 
Sun, the VAX and the RT.  Ugh.  Patches appended, though they are not
Officially Blessed

>2. Value returned by the pipe is not correct.

This looks like a race condition to me.

*** bash-1.02/execute_cmd.c	Sat Jul  1 21:44:45 1989
--- src-1.02/execute_cmd.c	Wed Jul 12 17:23:17 1989
***************
*** 491,494
  /* For catching RETURN in a function. */
  int return_catch_flag = 0;
  jmp_buf return_catch;
  

--- 491,495 -----
  /* For catching RETURN in a function. */
  int return_catch_flag = 0;
+ int return_return_val = 0;
  jmp_buf return_catch;
  
***************
*** 636,640
  		    if (return_val)
  		      {
! 			result = return_val;
  		      }
  		    else

--- 637,641 -----
  		    if (return_val)
  		      {
! 			result = return_return_val;
  		      }
  		    else

*** bash-1.02/builtins.c	Wed Jul  5 21:25:49 1989
--- src-1.02/builtins.c	Wed Jul 12 17:12:46 1989
***************
*** 1642,1645
    extern int last_command_exit_value;
    extern int return_catch_flag;
    extern jmp_buf return_catch;
    int return_val = get_numeric_arg ("return", list);

--- 1662,1666 -----
    extern int last_command_exit_value;
    extern int return_catch_flag;
+   extern int return_return_val;
    extern jmp_buf return_catch;
    int return_val = get_numeric_arg ("return", list);
***************
*** 1648,1651
      return_val = last_command_exit_value;
  
    if (return_catch_flag)
      longjmp (return_catch, return_val);

--- 1669,1673 -----
      return_val = last_command_exit_value;
  
+   return_return_val = return_val;
    if (return_catch_flag)
      longjmp (return_catch, 1);	/* force a 1 */
***************
*** 1649,1653
  
    if (return_catch_flag)
!     longjmp (return_catch, return_val);
    else {
      report_error ("can only `return' from a function");

--- 1671,1675 -----
    return_return_val = return_val;
    if (return_catch_flag)
!     longjmp (return_catch, 1);	/* force a 1 */
    else {
      report_error ("can only `return' from a function");



Chet Ramey			"We are preparing to think about contemplating 
Network Services Group, CWRU	 preliminary work on plans to develop a
chet@cwjcc.INS.CWRU.Edu		 schedule for producing the 10th Edition of 
				 the Unix Programmers Manual." -- Andrew Hume