c:\@Work\Perl>perl -wMstrict -le
"use Data::Dump qw(pp);
 ;;
 print 'perl version: ', $];
 ;;
 for my $s ('a1', qq{\x{1f}s}, qq{\x13}, qq{ab\x{13}cd}) {
   print q{'H*' found 0x13 in }, pp($s)
     if unpack('H*', $s) =~ m{ \A (?: ..)* 13 }xms;
   }
"
perl version: 5.008009
'H*' found 0x13 in "\23"
'H*' found 0x13 in "ab\23cd"