D:\>perl -E"my $x; BEGIN{$x=qr/a.*u/}; use re 'debug'; my $str = 'aou'; say $str
 =~ /$x/"
1

D:\>perl -E"my $x; BEGIN{$x=qr/a.*u/}; use re 'debug'; my $str = 'aou'; say $str
 =~ /$x/g"
aou