$re = qr/abc(def|ghi)(?:jkl)+/i;
open RE, "> my_re.pl" or die "can't write to my_re.pl: $!";
print RE $re;
close RE;

# later

open RE, "< my_re.pl" or die "can't read my_re.pl: $!";
chomp($re = <RE>);
close RE;