No, \u is ucfirst, \U is uc. Interestingly, either will work in redefining ucfirst. Perl knows that \u means Perl's own ucfirst, even if ucfirst has been redefined. 
BEGIN {
  *CORE::GLOBAL::ucfirst = sub {
    join ' ', map "\u$_", split / /, @_ ? $_[0] : $_;
  }
}

$_ = "one  two 'three' four\n";
print "\u$_";
print ucfirst;

[download]
And in fact, my original suggestion even works! Perl is way ahead of the DWIM curve. 
BEGIN {
  *CORE::GLOBAL::ucfirst = sub {
    join ' ', map ucfirst, split / /, @_ ? $_[0] : $_;
  }
}

$_ = "one  two 'three' four\n";
print "\u$_";
print ucfirst;

[download]
Update: fixed default-as-$_ code.
The PerlMonk tr/// Advocate

In reply to Re: Re: Globally change ucfirst in mod_perl by Roy Johnson
in thread Globally change ucfirst in mod_perl by dragonchild

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