Fix variable assignments in function invocations

Hello all,

A long-standing problem with dash has been how it deals with variable assignments in function invocations, and several packages are affected by it, two I've come across recently being autogen and pkg-config (only their test suites, luckily).

A short test script:

f() {
echo inside f, VAR is $VAR
sh -c 'echo inside sh called from f, VAR is $VAR'
}

VAR=value f
echo after returning from f, VAR is $VAR

Assuming VAR was not already set, this should print (and does with bash):

inside f, VAR is value
inside sh called from f, VAR is value
after returning from f, VAR is

With dash, this actually prints:

inside f, VAR is value
inside sh called from f, VAR is
after returning from f, VAR is value

The first problem with that is that VAR does not get exported, the second is that VAR's assigned value is kept after the function has returned.

Quoting SUSv4 Shell Command Language 2.9.1 Simple Commands:

If no command name results, variable assignments shall affect the current execution environment. Otherwise, the variable assignments shall be exported for the execution environment of the command and shall not affect the current execution environment (except for special built-ins).

In VAR=value f, f is found as the command name. No exception is made for function invocations, so I believe this disallows dash's current behaviour, and requires it to print the same thing bash does.

Fixing this seems trivial, see the attachment, and the test suites of both autogen and pkg-config pass with this change. Does this look correct?

Cheers,
Harald van Dijk

@@ -875,7 +875,7 @@ raise:
 		break;
 
 	case CMDFUNCTION:
-		poplocalvars(1);
+		listsetvar(varlist.list, VEXPORT|VSTACK);
 		if (evalfun(cmdentry.u.func, argc, argv, flags))
 			goto raise;
 		break;

This behavior is tricky. Here's the latest POSIX wording:
http://austingroupbugs.net/view.php?id=654#c1559

* If the command name is a function that is not a standard utility implemented as a function, variable assignments shall affect the current execution environment during the execution of the function. It is unspecified:

- Whether or not the variable assignments persist after the completion of the function

- Whether or not the variables gain the export attribute during the execution of the function

- Whether or not export attributes gained as a result of the variable assignments persist after the completion of the function (if variable assignments persist after the completion of the function)

So the existing dash behavior is compliant, even if different from bash.

This is the text that was rendered obsolete by the above POSIX bug 654.

I have no opinion on whether to take the patch in order to behave more like bash, or whether to tell script-writers to fix their script to avoid unspecified behavior because dash is already compliant in providing a different behavior than bash.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Thank you for the reference! I wasn't aware that the wording has since changed.

Well, perhaps it was already compliant, perhaps it became compliant by changing the standard, but either way, it is compliant now. :)

If either behaviour is allowed, then I believe dash aims to avoid breaking changes. Existing scripts written for dash could conceivably rely on the current behaviour, so without any real benefit, my patch would be a bad idea. bash compatibility is usually not considered a big benefit for dash, POSIX compatibility is.

Because of that, I withdraw my patch.

Cheers,
Harald van Dijk

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The currently-published standard (as far as I know, I7 TC1 has not been published yet) requires the dash behavior. Bash implements it in Posix mode. Both shells will remain conformant when TC1 comes out.

See
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_09_05

which includes

"When a function is executed, it shall have the syntax-error and variable- assignment properties described for special built-in utilities in the enumerated list at the beginning of Special Built-In Utilities."

- --
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU [email protected] http://cnswww.cns.cwru.edu/~chet/
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