I believe that qr/b/ and qr/(?-xism:b)/ are equivalent.

$perl -de 42
Reading ~/.perldb options.
 
Loading DB routines from perl5db.pl version 1.25
Editor support available.
 
Enter h or `h h' for help, or `man perldebug' for more help.
 
main::(-e:1):   42
  DB<1> $v = qr/b/
 
  DB<2> x $v
0  (?-xism:b)
   -> qr/(?-xism:b)/
[download]

If you are trying to store off persistent data and read it back in later, you might look at Storable