$string !~ /$pattern/

##</code><code>##

/(?:^\d|[_-]\d.)/

##</code><code>##

$ perl -E 'my @x = qw{aa1.2 aa1_bb2 aa1_2 aa1_2bb 1aa}; $_ !~ /(?:^\d|[_-]\d.)/ && say for @x'
aa1.2
aa1_bb2
aa1_2