If you look again at the original post, you’ll see that the forward slash which is there is functioning as a delimiter for the regex. But the forward shash to be matched is missing. That’s why I recommended using different delimiters for the regex: if the delimiter is something other than a slash, you don’t need to backslash the slash inside the regex. Too many back- and forward-slashes produce what is called “leaning toothpick syndrome.”

On the syntax for delimiters, see, e.g., perlretut#Simple-word-matching and perlop#Quote-and-Quote-like-Operators. Note that if you use any delimiter other than a forward slash, you need to prefix the regex with an m: /abc/ becomes m!abc! or m[abc], etc.

Hope that helps,