my $mystring = "perl monks"; 

# Oops, I thought it was supposed to span words. Thanks for the heads-up, kwaping
#(my $splitted = $mystring) =~ s/(?<=.)(\S)\s*(?=\S)/$1 $1/g;
(my $splitted = $mystring) =~ s/(?<=\S)(\S)(?=\S)/$1 $1/g;

print $splitted;