On Wed, July 16, 2008 10:56 am, Ronald J Kimball wrote:
>  On Wed, Jul 16, 2008 at 05:55:30AM -0700, Ulrich Windl wrote:
>  Thank you for your bug report.  Here's what the documentation for substr
>  has to say:
> 
>  If the lvalue returned by substr is used after the EXPR is changed in
>  any way, the behaviour may not be as expected and is subject to change.
>  This caveat includes code such as "print(substr($foo,$a,$b)=$bar)" or
>  "(substr($foo,$a,$b)=$bar)=$fud" (where $foo is changed via the sub-
>  string assignment, and then the substr is used again), or where a substr()
>  is aliased via a "foreach" loop or passed as a parameter or a reference to
>  it is taken and then the alias, parameter, or deref'd reference either is
>  used after the original EXPR has been changed or is assigned to and then
>  used a second time.

I blush whenever I read that (my) turgid paragraph and would still like
someone to make it more user-friendly.

>  That definitely seems to apply to your code above.  I'm not sure this is
>  technically a bug, so much as unspecified behavior.

It was explicitly unspecified because we wanted to change it (and I believe
did so in 5.10; I only have a 5.11 right now, so I'm not sure at what point
the change was introduced).  But neither 5.8.8 nor 5.11 produce the
results Ulrich is looking for.  He's expecting:

   perl -wle'$foo="abc"; print(substr($foo,0,1)="")'

to print "a", when in fact it prints "b" before 5.10 and "" after.

However, 4-arg substr does what he wants, replacing the range with
an empty string but returning its original contents:

$ perl -wle'$foo="abc"; print(substr($foo,0,1,""))'
a