Subroutine return value

[Daryl Lee]

In “Learning Perl”, Pg. 116, is found this sentence: Whatever calculation is 
last performed in a subroutine is automatically also the return value.

I have a subroutine that (almost) ends with this loop:

    foreach my $line (@lines) {
        $sum += evaluate($line);
  }

What I want to return is the final value of $sum as calculated on the last pass 
of that loop, so I simply closed the subroutine block right there with }, 
making it look like this:

    foreach my $line (@lines) {
        $sum += evaluate($line);
  }
}

That was pointless, so I “worked around” the issue by adding $sum at the end:

    foreach my $line (@lines) {
        $sum += evaluate($line);
  }
    $sum;
}

I think I can remember this in the future, but I’d like to understand what’s 
actually happening.   And I suspect I’m offending some veterans by not making 
Perl-ish use of #_.  Sorry about that.