Just a tangential word of caution, Andy; quoting (determining interpolation) matters:

C:>perl -e "my $var = '0x8';if ($var =~ /^[1-9]\d*$/) {print 'num' } e
+lse {print 'not a num';}"
not a num
[download]

But

C:>perl -e "my $var = 0x8;if ($var =~ /^[1-9]\d*$/) {print 'num' } els
+e {print 'not a num';}"
num
[download]