misc/132182: uname(1) uses UNAME_<flag> variables even if those are empty

[Jan Schaumann]

>Number:         132182
>Category:       misc
>Synopsis:       uname(1) uses UNAME_<flag> variables even if those are empty
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sat Feb 28 00:00:12 UTC 2009
>Closed-Date:
>Last-Modified:
>Originator:     Jan Schaumann
>Release:        
>Organization:
>Environment:
>Description:
uname(1) on FreeBSD has the interesting feature that one can set, say, UNAME_r to a string and 'uname -r' will report that string.  However, it will also report that string if UNAME_r is set in the environment but empty.

I believe that is a bug, since the intention is to use the UNAME_r variable as specified by the user, but the user may wish to change this back to the default.

Yes, this can be worked around by using 'unset'; however, in some instances this isn't possible:  consider a crontab where an entry needs to execute using the variable, but other crontabs must not:

UNAME_r=foo
0 * * * * whatever
UNAME_r=
* * * * * another


Using 'unset' is not an option in this scenario, nor is "remembering" the previous value in a temporary variable a la "UNAME_r_orig=$(uname -r)".
>How-To-Repeat:
export UNAME_r="foo"
uname -r
export UNAME_r=
uname -r
>Fix:
diff -b -u -r1.14 uname.c
--- uname.c     1 Jul 2003 20:15:28 -0000       1.14
+++ uname.c     27 Feb 2009 23:52:52 -0000
@@ -134,7 +134,8 @@

 #define        CHECK_ENV(opt,var)                              \
 do {                                                   \
-       if ((var = getenv("UNAME_" opt)) == NULL) {     \
+       if (((var = getenv("UNAME_" opt)) == NULL) ||   \
+               (strlen(var) == 0)) {                   \
                get_##var = native_##var;               \
        } else {                                        \
                get_##var = (get_t)NULL;                \


>Release-Note:
>Audit-Trail:
>Unformatted: