Re: [PATCH] Yet another shell function prerequisite!

[Eric Blake]

Paolo Bonzini <bonzini <at> gnu.org> writes:

> > In the meanwhile I thought about
> > 
> >   as_lineno=${as_lineno-$LINENO} func
> > 
> > which is a slick trick, as it supports nesting and does not require
> > unset.  
> 
> ... and fails in bash 2.x, of course.

Maybe I couldn't reproduce the failure in bash 2.x, but I do see it in Solaris 
8 /bin/sh:

$ func_var(){ echo $a;}
$ func_var

$ a=b func_var  

$

Even worse, bash 3.2 is bipolar:

$ bash -c 'func(){ echo "${a+set}";}; a=1 func; echo $a'
set

$ bash -c 'set -o posix;func(){ echo "${a+set}";}; a=1 func; echo $a'
set
1
$

In other words, asking bash for POSIX compliance actually makes bash violate 
POSIX by leaking the assignment beyond the function call; since POSIX requires 
that "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)."

pdksh has the same bug as "Posix-mode" bash.

In summary, asking a shell to temporarily assign environment variables for the 
duration of a function call is not portable.  So I'm installing this:

From: Eric Blake <address@hidden>
Date: Tue, 14 Oct 2008 11:26:58 -0600
Subject: [PATCH] Document shell function environment pitfall.

* doc/autoconf.texi (Shell Functions): Document bugs in bash,
Solaris /bin/sh.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog         |    6 ++++++
 doc/autoconf.texi |   17 +++++++++++++++++
 2 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index d6337f6..071f2a9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2008-10-14  Eric Blake  <address@hidden>
+
+       Document shell function environment pitfall.
+       * doc/autoconf.texi (Shell Functions): Document bugs in bash,
+       Solaris /bin/sh.
+
 2008-10-14  Paolo Bonzini  <address@hidden>
 
        Use m4_require to implement AS_REQUIRE.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index ff81c2e..dc86462 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -14225,6 +14225,23 @@ Shell Functions
 and other options upon function entry and exit.  Inside a function,
 @acronym{IRIX} sh sets @samp{$0} to the function name.
 
+It is not portable to pass temporary environment variables to shell
+functions.  Solaris @command{/bin/sh} does not see the variable.  Meanwhile,
address@hidden 3.2 breaks the Posix rule that the assignment must not affect
+the current environment, but only when Posix compliance is requested!
+
address@hidden
+$ @kbd{/bin/sh -c 'func()@{ echo $a;@}; a=1 func; echo $a'}
address@hidden
address@hidden
+$ @kbd{bash -c 'func()@{ echo $a;@}; a=1 func; echo $a'}
address@hidden
address@hidden
+$ @kbd{bash -c 'set -o posix; func()@{ echo $a;@}; a=1 func; echo $a'}
address@hidden
address@hidden
address@hidden example
+
 Some ancient Bourne shell variants with function support did not reset
 @address@hidden, @var{i} >= 0}, upon function exit, so effectively the
 arguments of the script were lost after the first function invocation.
-- 
1.6.0.2