G'day Polyglot,

TMTOWTDI

$ perl -E '
    my @many_strings = ("abc", "cd", "e", "fg", "hi", "hello world");
    $" = "";
    say length "@many_strings";
'
21
[download]

Although, I'd generally localise changes to special variables in the smallest scope possible:

$ perl -E '
    my @many_strings = ("abc", "cd", "e", "fg", "hi", "hello world");
    {
        local $" = "";
        say length "@many_strings";
    }
'
21
[download]

Update: I checked to see if anyone had used that prior to posting. Obviously, I didn't look closely enough: after posting I noticed ++hippo had already posted the same solution.