Bug 1389838

Summary:	command builtin should not abort on variable assignment errors
Product:	[Fedora] Fedora	Reporter:	Denys Vlasenko <dvlasenk>
Component:	bash	Assignee:	Siteshwar Vashisht <svashisht>
Status:	CLOSED ERRATA	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	26	CC:	admiller, kdudka, svashisht
Target Milestone:	---
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:	bash-4.4.12-5.fc26	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2017-06-09 19:15:24 UTC	Type:	Bug
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
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Description Denys Vlasenko 2016-10-28 20:19:25 UTC

Shell has a concept of "special builtin utilities":
builtins which are special have a few properties which are different from the builtins which are merely optimizations (for example, "echo" builtin is not special, it is an optimization: we don't want to fork an entire process in order to print a few bytes).

In particular:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html
"2.14. Special Built-In Utilities
...
A syntax error in a special built-in utility may cause a shell executing that utility to abort, while a syntax error in a regular built-in utility shall not cause a shell executing that utility to abort."

However.

There is a (regular, non-special) builtin, "command":
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html
which is required to "nullify" this effect:
"If the command_name is the same as the name of one of the special built-in utilities, the special properties in the enumerated list at the beginning of 'Special Built-In Utilities' shall not occur."

The bug is that in Posix mode (for example, if called as "sh", not "bash"), bash aborts in this example:

sh -c 'readonly VAR=123; command eval "VAR=123"; echo $?'

The bug is that "echo $?" command is not executed: shell aborted execution before reaching it.

There exist scripts which use this construct to detect whether a given variable is read-only.

Comment 1 Fedora End Of Life 2017-02-28 10:31:39 UTC

This bug appears to have been reported against 'rawhide' during the Fedora 26 development cycle.
Changing version to '26'.

Comment 2 Siteshwar Vashisht 2017-04-28 11:47:45 UTC

https://lists.gnu.org/archive/html/bug-bash/2017-04/msg00144.html

Comment 3 Siteshwar Vashisht 2017-04-28 13:55:36 UTC

diff --git a/subst.c b/subst.c
index 65e7d08..998b850 100644
--- a/subst.c
+++ b/subst.c
@@ -10863,11 +10863,12 @@ expand_word_list_internal (list, eflags)
                  tint = do_word_assignment (temp_list->word, 0);
                  this_command_name = savecmd;
                  /* Variable assignment errors in non-interactive shells
-                    running in Posix.2 mode cause the shell to exit. */
+                    running in Posix.2 mode cause the shell to exit, unless
+                    they are being run by the `command' builtin. */
                  if (tint == 0)
                    {
                      last_command_exit_value = EXECUTION_FAILURE;
-                     if (interactive_shell == 0 && posixly_correct)
+                     if (interactive_shell == 0 && posixly_correct && executing_command_builtin == 0)
                        exp_jump_to_top_level (FORCE_EOF);
                      else
                        exp_jump_to_top_level (DISCARD);

Comment 4 Fedora Update System 2017-05-30 05:40:50 UTC

bash-4.4.12-5.fc26 has been submitted as an update to Fedora 26. https://bodhi.fedoraproject.org/updates/FEDORA-2017-84add424bf

Comment 5 Fedora Update System 2017-05-30 21:46:52 UTC

bash-4.4.12-5.fc26 has been pushed to the Fedora 26 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2017-84add424bf

Comment 6 Fedora Update System 2017-06-09 19:15:24 UTC

bash-4.4.12-5.fc26 has been pushed to the Fedora 26 stable repository. If problems still persist, please make note of it in this bug report.