# delimiter is X
$escaped_str = <<'EOT'; 
Xa\X\\bXc\\XdX
EOT
chomp $escaped_str;

@a = split(/X/ ,$escaped_str, -1);

print "(",join(':',@a),")";
# gives:  (:a\:\\b:c\\:d:)
# want:   (:a\X\\b\\:c\\:d:)