What is variable suicide and how can I prevent it?

    Variable suicide is a nasty sideeffect of dynamic scoping and
    the way variables are passed by reference.  If you say

        $x = 17;
        &munge($x);
        sub munge {
            local($x);
            local($myvar) = $_[0];
            ...
        } 

    Then you have just clubbered $_[0]!  Why this is occurring 
    is pretty heavy wizardry: the reference to $x stored in 
    $_[0] was temporarily occluded by the previous local($x)
    statement (which, you're recall, occurs at run-time, not
    compile-time).  The work around is simple, however: declare
    your formal parameters first:

        sub munge {
            local($myvar) = $_[0];
            local($x);
            ...
        }

    That doesn't help you if you're going to be trying to access
    @_ directly after the local()s.  In this case, careful use
    of the package facility is your only recourse.

    Another manifestation of this problem occurs due to the
    magical nature of the index variable in a foreach() loop.

        @num = 0 .. 4;
        print "num begin  @num\n";
        foreach $m (@num) { &ug }
        print "num finish @num\n";
        sub ug {
            local($m) = 42;
            print "m=$m  $num[0],$num[1],$num[2],$num[3]\n";
        }
    
    Which prints out the mysterious:

        num begin  0 1 2 3 4
        m=42  42,1,2,3
        m=42  0,42,2,3
        m=42  0,1,42,3
        m=42  0,1,2,42
        m=42  0,1,2,3
        num finish 0 1 2 3 4

    What's happening here is that $m is an alias for each 
    element of @num.  Inside &ug, you temporarily change
    $m.  Well, that means that you've also temporarily 
    changed whatever $m is an alias to!!  The only workaround
    is to be careful with global variables, using packages,
    and/or just be aware of this potential in foreach() loops.

    The perl5 static autos via "my" will not have this problem.