0001425: exit in an EXIT trap is not clearly specified

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Category

Severity

Type

Date Submitted

Last Update

0001425

[1003.1(2016/18)/Issue7+TC2] Shell and Utilities

Objection

Error

2020-11-23 23:10

2024-06-11 09:08

Reporter

kre

View Status

public

Assigned To

Priority

normal

Resolution

Accepted As Marked

Status

Closed

Name

Robert Elz

Organization

User Reference

Section

XCU 2.14 / exit

Page Number

2399

Line Number

76764-5

Interp Status

---

Final Accepted Text

Note: 0005266

Summary

0001425: exit in an EXIT trap is not clearly specified

Description

the page for the special builtin command "exit" says

    A trap on EXIT shall be executed before the shell terminates,
    except when the exit utility is invoked in that trap itself,
    in which case the shell shall exit immediately.

The issue is what "that trap itself" means.

Consider

   $SHELL -c 'trap "trap \"echo bar\" EXIT; echo foo; exit" EXIT'

When the exit command in the outer exit trap is executed, the EXIT
trap has been changed to be something different, that is, the
shell is not executing the (current) EXIT trap when that exit command
is executed, so by a literal reading of the standard, the inner trap
should fire, and the shell should print

    foo
    bar

before exiting.

That is what the FreeBSD and NetBSD shells, and bosh, mksh, and zsh do.
bash yash ksh93 and dash print only "foo", that is they seem to ignore
the "that" in "that exit trap" and treat the text as if it said

    except when the exit utility is invoked in an exit trap

The page in XCU 2.14 for trap says nothing pertinent to this issue
(I am not suggesting that it should, just noting it).

Desired Action

Since the "reference" shells seem to do this the broken way, it is
unlikely that the standard will have words (or an example) added to
reinforce the current wording (I am guessing).

But since the other shells are doing exactly what the standard requires
of them, it would be incorrect, and unfair to specify this so as to
require the currently non-standard behaviour that the reference shells
implement.

Given that, the best that can be done, I believe, is to add a new
sentence, immediately after the one quoted above (which is unchanged
in 202x drafts) something like

    It is unspecified whether an EXIT trap defined while executing
    a previous EXIT trap will be executed before the shell terminates
    after completing execution (via an exit command, or reaching the
    end) of the earlier EXIT trao.

Tags

tc3-2008

Attached Files

Relationships

Notes
(0005266) rhansen (manager) 2021-03-11 17:07	In c181 on page 2399 append another sentence to the paragraph at lines 76764-76765: It is unspecified whether setting a new trap action on EXIT during execution of a trap action on EXIT will cause the new trap action to be executed before the shell terminates.

Issue History
Date Modified	Username	Field	Change
2020-11-23 23:10	kre	New Issue
2020-11-23 23:10	kre	Name	=> Robert Elz
2020-11-23 23:10	kre	Section	=> XCU 2.14 / exit
2020-11-23 23:10	kre	Page Number	=> 2399
2020-11-23 23:10	kre	Line Number	=> 76764-5
2021-03-11 17:07	rhansen	Note Added: 0005266
2021-03-11 17:08	rhansen	Interp Status	=> ---
2021-03-11 17:08	rhansen	Final Accepted Text	=> Note: 0005266
2021-03-11 17:08	rhansen	Status	New => Resolved
2021-03-11 17:08	rhansen	Resolution	Open => Accepted As Marked
2021-03-11 17:09	rhansen	Tag Attached: tc3-2008
2021-03-25 14:27	geoffclare	Status	Resolved => Applied
2024-06-11 09:08	agadmin	Status	Applied => Closed

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