use warnings;
use strict;

my $text = "I am a GIRL, a Real GIRL. A test WITH Multiple conDITions AND other tests.";

print map{"$_ "}
      map{$_ = lc($_) unless (($_ eq uc $_) and length $_ > 1 ); $_ }
      map{split ' ',$_}$text;
      
__END__
Prints: 
i am a GIRL, a real GIRL. a test WITH multiple conditions AND other tests.