use strict;
use warnings;

use 5.010;
use feature qw(say);

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

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

}

# Main
outer_sub();
exit(0);
__END__
[22:16:28.33] c:\test>junk41
Outer Subroutine Start ...
PARAM: 0
Start inner_sub1
PARAM: 1
Outer Subroutine End.