use strict;
use warnings;

use lib 'C:\scripts';

package Foo;

sub bar {
    print "I am bar from Foo.\n";
}

package main;

no warnings 'redefine';
*Foo::real_bar = \&Foo::bar;
*Foo::bar = sub {
    print "I am bar NEW!\n";
    Foo->real_bar;
    *Foo::bar = \&Foo::real_bar;
};
&print_stuff;

sub print_stuff {
    &print_bar1;
    &print_bar2;
}

sub print_bar1 {
    Foo->bar;
}

sub print_bar2 {
    Foo->bar;
}

####################
OUTPUT:
plxc16479> $h2/scripts/tmp.pl
 # output from redefined sub
I am bar NEW!
 # output from original sub called from inside redefined sub
I am bar from Foo.
 # output from original sub after being redefined back
I am bar from Foo.