I understand the usage of local and  my.
But can anyone explain what's "a variable global within the current block" and when do you want to do that?

Imagine you had a package:

package MyPack;
my $a;
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As defined above, there is no way for anything outside the scope of MyPack to access $a. Of course, with Exporter and a few other standard class tricks, this is not hard to fix, but using Exporter for every class is a nuicence.

Using 'our' makes the variable known at the global scope level (that is, everyone can access it now):

package MyPack;
our $a;
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Anywhere outside of MyPack, I can now get the value of $a via the variable $MyPack::a.

So 'our' can be considered to be declaring which variables are public in a object-oriented sense. It mostly replaces the functionality of Exporter which can be awkward to use.

---

Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain

Never. (: Use use vars when you need a package global, such as a variable you plan to export. This is the same case when you might want to use our but doing so just makes your code less portable. If you aren't writing a module, then my is what you should use nearly all of the time. See other response for more information on some of the exceptions.

For an indepth analysis of this look no further than the 
pages of the the one and only M-J. Dominus.

Short answer (stolen from MJD)

'Always use my, never use local.'

To learn about namespaces my/our/local see:
Coping with Scoping
http://perl.plover.com/FAQs/Namespaces.html

In this next article MJD partially recants from the brief advice
to never use local, always use my

Seven Useful Uses of local 
http://perl.plover.com/local.html

Hope this helps, I found these articles very useful

Cheers

tachyon

my $answer =[q;7566626f206f7420756f7920656d6f636c65772049;];
print join''=>reverse split''=>pack H42=>$answer->[0]=>eval;
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(there is no section for "modules" so I put it under subs, since the my/local was there.)

—John