Wouldn't it be easier to do

       join ' ', map {ucfirst} split / /, shift;
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Can't use ucfirst when you're redefining it, can you?
Update: Actually, you can!
I'll take my Bonehead Award anytime it's ready. Make it:

        join ' ', map { s/^(.)/\U$1/; $_ } split / /, shift
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That should work, right, since it's using uc instead of ucfirst.

To do it with pure s///:

       (my $f=shift)=~s/(^| )(\w)/$1\U$2/g;
       # Doing it with lookbehind gets a little ugly:
       # s/(?:(?<=^)|(?<= ))(\w)/\U$1/g;
       $f;
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