A NOTE has been added to this issue. ====================================================================== https://www.austingroupbugs.net/view.php?id=1309 ====================================================================== Reported By: kre Assigned To: ====================================================================== Project: 1003.1(2016)/Issue7+TC2 Issue ID: 1309 Category: Shell and Utilities Type: Enhancement Request Severity: Objection Priority: normal Status: New Name: Robert Elz Organization: User Reference: Section: 2.9.4 Page Number: 2371-4 Line Number: 75726-31 Interp Status: --- Final Accepted Text: ====================================================================== Date Submitted: 2019-12-19 02:26 UTC Last Modified: 2020-01-20 18:37 UTC ====================================================================== Summary: Clarity needed for initial value of $? at start of compound-list compound statements ====================================================================== Relationships ID Summary ---------------------------------------------------------------------- related to 0001150 exit status of command substitution not... related to 0000051 sh exit status not clear for built-in t... ======================================================================
---------------------------------------------------------------------- (0004743) kre (reporter) - 2020-01-20 18:37 https://www.austingroupbugs.net/view.php?id=1309#c4743 ---------------------------------------------------------------------- This (https://www.austingroupbugs.net/view.php?id=1309#c4742) is mostly all good (the two minor issues I have with it are just below) but note that this is really a side issue that developed from this bug report, I still believe that it would be good to add (and certainly harmless) some words to the effect of When the list begins execution, the value of the special parameter ? shall be that produced by evaluation of the condition-list that immediately preceded this execution of the list applied to if/while/until statements (or somewhere common and stated to apply to all such commands) - that is, to clarify that even though the exit status ($?) from the condition list is not available after one of these compound commands completes (regardless of being the last command executed as part of the compound command) its exit status is available inside the code that is the body of the compound command. My reservations with the wording in the note relate first to this part Note: In <tt>var=$(some_command); echo $?</tt> the output is the exit status of <tt>some_command</tt>, which is all fine, until its exit status becomes the exit status of the assignment command <tt>var=$(some_command)</tt> There is no such thing as an "assignment command". What there is is variable assignments, and null commands, What 2.9.1 says is ... If there is no command name, but the command contained a command substitution, the command shall complete with the exit status of the last command substitution performed. Otherwise, the command shall complete with a zero exit status. which does not invent an "assignment command" - but even if it did would not cover cases like umask 0; >/tmp/foo; # this is just to create a known environment </tmp/foo$(exit 1) which in all shells except bash and zsh (all I have tested anyway) results in $? being set to 1 - since on that 2nd line, there is no command name, but there is a command substitution, so the status of the last of those (here there is just one) becomes the status of this empty command (as 2.9.1 directs). 2.9.1 also says: If there is no command name, any redirections shall be performed in a subshell environment; it is unspecified whether this subshell environment is the same one as that used for a command substitution within the command. which, since it says "unspecified" might seem to be relevant, but I don't believe it is, whether the redirect happens in the same subshell as the command substitution isn't really relevant, there is no command name (except exit, which is the command substitution command) and so the exit status here should be the status of the (last) command substitution performed. Anyway, inventing a fictional assignment command doesn't help, and I don't think is needed - I don't believe any reference to x=$(whatever) is needed in this context at all. What is the exit status of various commands (including simple commands without command names, which is what this is) is specified elsewhere, and doesn't need to also be specified in the definition of the ? special parameter. Second reservation: there is no need for When a subshell environment is created, it is unspecified whether the value of the special parameter '?' from the invoking shell environment is preserved in the subshell or the value is reset to 0. It is preserved, and if we need say anything at all (I have no issues with saying something here, more clarity is helpful) it should be When a subshell environment is created, the value of the special parameter ? shall initially be the value it had in the shell environment immediately preceding the creation of the subshell environment. (or words something like that which better meet the standard language). Perhaps just: Creating a subshell environment does not alter the value of the special parameter ? Joerg already cleared up the apparent issue with ksh and the strange 0 status from the test - it is not $? that is incorrect there, but "exit" and that is an obvious bug, and not worthy of any mention in the standard at all. Note that all shells print 1 for (exit 1); (echo $?) including ksh93 (and I presume ksh88). That makes it clear that it is not the subshell environment that is causing the 0 from (exit 1); (exit) ; echo $? in ksh, but a bug in the exit command (my guess would be that it is attempting to do what the standard seems to say, looking for the status of the "last command" and failing to find one in its current environment, and consequently defaulting to 0. That's bogus, but practically harmless, as no-one in real code writes a subshell in which the first command is exit (without a specific exit value) as all that would be is an expensive no-op. Issue History Date Modified Username Field Change ====================================================================== 2019-12-19 02:26 kre New Issue 2019-12-19 02:26 kre Name => Robert Elz 2019-12-19 02:26 kre Section => 2.9.4 2019-12-19 02:26 kre Page Number => 2371-4 2019-12-19 02:26 kre Line Number => 75726-31 2020-01-16 17:42 geoffclare Note Added: 0004731 2020-01-16 17:43 geoffclare Note Edited: 0004731 2020-01-16 20:35 kre Note Added: 0004732 2020-01-16 21:36 kre Note Added: 0004733 2020-01-17 04:17 kre Note Added: 0004734 2020-01-17 04:19 kre Note Edited: 0004734 2020-01-17 09:56 joerg Note Added: 0004735 2020-01-17 10:31 kre Note Added: 0004736 2020-01-17 15:39 geoffclare Note Added: 0004737 2020-01-17 15:53 joerg Note Added: 0004738 2020-01-17 15:56 joerg Note Edited: 0004738 2020-01-17 16:04 joerg Note Edited: 0004738 2020-01-17 16:17 geoffclare Note Edited: 0004737 2020-01-18 02:38 kre Note Added: 0004739 2020-01-20 11:57 geoffclare Note Added: 0004741 2020-01-20 14:54 geoffclare Note Added: 0004742 2020-01-20 14:55 geoffclare Note Edited: 0004742 2020-01-20 14:58 geoffclare Relationship added related to 0001150 2020-01-20 15:04 geoffclare Relationship added related to 0000051 2020-01-20 18:37 kre Note Added: 0004743 ======================================================================
