use re 'debug';
$x = "\\B";
$y = "Here is \\B";
print $y =~ /$x/ ? "y" : "n";
__END__
Compiling REx `\B'
size 2 Got 20 bytes for offset annotations.
first at 1
   1: NBOUND(2)
   2: END(0)
stclass "NBOUND" minlen 0
Offsets: [2]
        1[2] 3[0]
Matching REx "\B" against "Here is \B"
Matching stclass "NBOUND" against "Here is \B"
  Setting an EVAL scope, savestack=3
   1 <H> <ere is \B>      |  1:  NBOUND
   1 <H> <ere is \B>      |  2:  END
Match successful!
yFreeing REx: `"\\B"'