What have you tried so far? Do you know about the built-in functions ucfirst and lc ? You might also find the \L regex operator useful:

my @words = qw/mY WoRd THIS is A mEsS/;
for ( @words ) {
    (my $downcased = $_) =~ s/(\w+)/\L$1/;
    print join( " ", $_, $downcased, ucfirst(lc), uc ), "\n";
}

__OUTPUT__
mY my My MY
WoRd word Word WORD
THIS this This THIS
is is Is IS
A a A A
mEsS mess Mess MESS
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