16:57 >perl -we "my $q = qr/^(\d+)$/; 123 =~ $q; print qq[$1\n];"
123

16:57 >perl -MO=Deparse -we "my $q = qr/^(\d+)$/; 123 =~ $q; print qq[$1\n];"
BEGIN { $^W = 1; }
my $q = qr/^(\d+)$/;
123 =~ /$q/;
print "$1\n";
-e syntax OK

16:57 >