use strict;
use warnings;

use 5.010;
use feature qw(say);

sub outer_sub {
    
    say "Outer Subroutine Start ...";
    my $param = 0;
    say "PARAM: $param";
    $param = inner_sub($param);
    say "PARAM: $param";
    say "Outer Subroutine End.";

    sub inner_sub {
        my $param = shift;
        say "Start inner_sub1";
        return ++$param;
    }
}

# Main
outer_sub();
exit(0);
__END__

Outer Subroutine Start ...
PARAM: 0
Start inner_sub1
PARAM: 1
Outer Subroutine End.