Perl use lib, unshift difference

What's the difference between use, unshift and PERL5LIB when adding/including module path?

A.

use lib - is a compile time inclusion. Try this example:

#! /usr/bin/perl -w

use strict;

print "@INC\n";
use lib '/home/kdranjan/Perl/Dynamic';
Print "@INC\n";

Run it and it will display: (Both are same because added path was included at compile time)
---------------------------
- /home/kdranjan/Perl/Dynamic /etc/perl /usr/local/lib/perl/5.10.0 /usr/local/share/perl/5.10.0 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.10 /usr/share/perl/5.10 /usr/local/lib/site_perl .

- /home/kdranjan/Perl/Dynamic /etc/perl /usr/local/lib/perl/5.10.0 /usr/local/share/perl/5.10.0 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.10 /usr/share/perl/5.10 /usr/local/lib/site_perl .


==========================================================

unshift - is a run time inclusion.


Modify previous script a bit like this:
---------------------------------------
#! /usr/bin/perl -w

use strict;

print "@INC\n";
unshift(@INC, '/home/kdranjan/Perl/Dynamic');
print "@INC\n";


- /etc/perl /usr/local/lib/perl/5.10.0 /usr/local/share/perl/5.10.0 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.10 /usr/share/perl/5.10 /usr/local/lib/site_perl .

- /home/kdranjan/Perl/Dynamic /etc/perl /usr/local/lib/perl/5.10.0 /usr/local/share/perl/5.10.0 /usr/lib/perl5 /usr/share/perl5 /usr/lib/perl/5.10 /usr/share/perl/5.10 /usr/local/lib/site_perl .