$ perl -wle'use re "debug"; $x = "foo\nbar"; qr/hullo #there $x/x'
Compiling REx `hullo #there $x'
size 4 Got 36 bytes for offset annotations.
first at 1
   1: EXACT <hullo>(4)
   4: END(0)
anchored `hullo' at 0 (checking anchored isall) minlen 5 
Offsets: [4]
        1[15] 0[0] 0[0] 16[0] 
Name "main::x" used only once: possible typo at -e line 1.
Freeing REx: `"hullo #there $x"'