You can't.

To access both variables the inner and outside variables must be in different packages. In fact, all you are doing in the code above is overwriting the old value (10) with a new value (11).

To be able to access two variables with the same name at the same time, you would have to do something like this:

package Frick;

# this variable will have the full name $Frick::a;
#our makes the variable sharable between packages
our $a=10;
{
  package Frack;

  # This variable will have the full name $Frack::b;
  # my limits $Frack::b to the package Frack.
  # No other package will be able to see or use its value
  my $a=11;

   print "Frick says $Frick::a, Frack says $a, $Frack::a\n";
  #prints: frick says: 10, frack says: 11, 11;
}
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Sorry,

The variable declared as my.

Rewriting the code

my $a=10;
{
   my $a=11;
   print $a;
}
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Please consider the file is not an module. It is just simple .pl file.

I want print value of $a is 10 inside the block which is declared on outside.

You still can't access the outer value without putting the variables in separate packages and declaring the outer one with our. The second inner my declaration "hides" the first outer my declaration. If you want to access two variables with the same name, you have to give them separate packages, even if it all happens in a single .pl file.

Packages aren't necessarily modules. You can have many package declarations in a single file and many files sharing the same package declaration. Packages are just namespaces you can use to group together variables and scope them logically rather than via text position (inside/outside curly braces).

If you really, really don't want to use packages to scope your variables, then you will have to give your inner and outer variables different names. Is there a particular reason you aren't doing that already?

In case the inner scope isn't just a plain block, but a subroutine, you can use PadWalker to get at the outer scope(s):

use PadWalker qw(peek_my);

my $a=10;
sub {
    my $a=11;
    my $my = peek_my(1);    # one level up

    print ${$my->{'$a'}};   # 10
    print $a;               # 11
}->();
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This isn't meant for everyday consumption, though... — better use unambiguous variable names.

Do it before you override it

The solution to your problem is by making the outer scoped variable a package variable using our, and referring to it using the implicit main package. The nested variable is a local variable using my. The full routine then becomes

#!/usr/bin/perl

use strict;
use warnings;

our $a = 10;
{
  my $a = 11;
  print $a, "\n"; # prints the local variable
  print $main::a, "\n"; # prints the package variable
}
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That said, it is also a trick question during your interview, as you mentioned. Choosing $a or $b for a local variable is always bad, because they are used by sort which means they are somewhat special and can cause strange behaviour.

#!/usr/local/bin/perl
print  __PACKAGE__ ;
print "\n";
$a=10;
{
  $a=11;
  print $a,"\n";
  print  __PACKAGE__ ;
}
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