0000760: asynchronous list assignment of stdin should depend on job control

ID	Project	Category	View Status	Date Submitted	Last Update

0000760	1003.1(2013)/Issue7+TC1	Shell and Utilities	public	2013-10-07 09:56	2019-06-10 08:55

Reporter	geoffclare	Assigned To
Priority	normal	Severity	Objection	Type	Error
Status	Closed	Resolution	Accepted

Name	Geoff Clare
Organization	The Open Group
User Reference
Section	2.9.3.1
Page Number	2342
Line Number	74502
Interp Status	Approved
Final Accepted Text	See 0000760:0001929


Summary	0000760: asynchronous list assignment of stdin should depend on job control
Description	XCU 2.9.3.1 Asynchronous Lists states: The standard input for an asynchronous list, before any explicit redirections are performed, shall be considered to be assigned to a file that has the same properties as /dev/null. If it is an interactive shell, this need not happen. What matters here is not whether the shell is interactive or not, but whether job control is enabled or not. Also, I'm not sure why this behaviour is allowed when job control is enabled. It means that users cannot rely on being able to start an interactive program in the background and then use "fg" to bring it to the foreground when they need to provide it with some input (having been notified that it was stopped with SIGTTIN). The desired action disallows the behaviour when job control is enabled, as I believe this change would be non-controversial. However, if this change is not felt to be appropriate for TC2, it could be deferred until Issue 8 (in which case the change in TC2 should say "may" instead of "shall not").
Desired Action	Change: The standard input for an asynchronous list, before any explicit redirections are performed, shall be considered to be assigned to a file that has the same properties as /dev/null. If it is an interactive shell, this need not happen. to: If job control is disabled (see set -m), the standard input for an asynchronous list, before any explicit redirections are performed, shall be considered to be assigned to a file that has the same properties as /dev/null. This shall not happen if job control is enabled.
Tags	tc2-2008

nick 2013-10-17 15:50 manager bugnote:0001929	Interpretation response ------------------------ The standard states that interactive shells need not reassign standard input, and conforming implementations must conform to this. However, concerns have been raised about this which are being referred to the sponsor. Rationale: ------------- This does not match existing practice. Notes to the Editor (not part of this interpretation): ------------------------------------------------------- Make the changes suggested in the Desired Action.

ajosey 2014-02-21 15:39 manager bugnote:0002154	Interpretation Proposed 21 Feb 2014

ajosey 2014-03-25 13:41 manager bugnote:0002197	Interpretation Approved: 25 March 2014

stephane 2019-06-08 06:11 reporter bugnote:0004410	Even for non-interactive shells, redirecting stdin to /dev/null when asynchronous is not particularly useful, and has to be worked around probably at least as often as it is useful. Some shells don't do it. zsh never does it, bash does not do it when that asynchronous list is one single pipeline. It may be more useful to leave it unspecified then (that might have been the original intention behind the original text: don't do it when interactive, unspecified when not). It may help to add an informative section that shows how to work around it: "{ cmd <&3 3<&- & } 3<&0" instead of "cmd &" BTW, that whole 2.9.3.1 section is incorrect as it refers to "commands" instead of "AND-OR lists". The whole part about the PID doesn't make sense in the context of an "AND-OR list" with more than one part. I'll raise a separate issue about that.

stephane 2019-06-08 06:24 reporter bugnote:0004411 Last edited: 2019-06-08 06:28	According to 2.9.3.1's "In all cases, explicit redirection of standard input shall override this activity" cmd <&0 & should be another work around. While that works in bash, yash (and of course zsh), it doesn't in bosh, dash, ksh93, pdksh, ksh88 (even /usr/xpg4/bin/sh on Solaris). The wording should be updated to say something like: wherever that happens, it shall happen before the explicit redirection of the command are processed. An implementation may choose not to do it at all if the stdin of the command is redirected.

geoffclare 2019-06-10 08:46 manager bugnote:0004413	The changes arising from this bug were applied in POSIX.1-2008 TC2, so this is not the right place to request further changes. (All of the bugs tagged tc2-2008 should have been closed some time ago to prevent this situation arising.) Re: 0000760:0004411 <&0 is a no-op, so it's unclear whether it counts as "explicit redirection of standard input".

Date Modified	Username	Field	Change
2013-10-07 09:56	geoffclare	New Issue
2013-10-07 09:56	geoffclare	Name	=> Geoff Clare
2013-10-07 09:56	geoffclare	Organization	=> The Open Group
2013-10-07 09:56	geoffclare	Section	=> 2.9.3.1
2013-10-07 09:56	geoffclare	Page Number	=> 2342
2013-10-07 09:56	geoffclare	Line Number	=> 74502
2013-10-07 09:56	geoffclare	Interp Status	=> ---
2013-10-17 15:50	nick	Interp Status	--- => Pending
2013-10-17 15:50	nick	Note Added: 0001929
2013-10-17 15:50	nick	Status	New => Interpretation Required
2013-10-17 15:50	nick	Resolution	Open => Accepted
2013-10-17 15:50	nick	Final Accepted Text	=> See 0000760:0001929
2013-10-17 15:59	nick	Tag Attached: tc2-2008
2014-02-21 15:39	ajosey	Interp Status	Pending => Proposed
2014-02-21 15:39	ajosey	Note Added: 0002154
2014-03-25 13:41	ajosey	Interp Status	Proposed => Approved
2014-03-25 13:41	ajosey	Note Added: 0002197
2019-06-08 06:11	stephane	Note Added: 0004410
2019-06-08 06:24	stephane	Note Added: 0004411
2019-06-08 06:28	stephane	Note Edited: 0004411
2019-06-10 08:46	geoffclare	Note Added: 0004413
2019-06-10 08:55	agadmin	Status	Interpretation Required => Closed
2019-07-15 15:38	Don Cragun	Relationship added	related to 0001254

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