Meaning of pound (#) in a regular expression

Question

I have a regular expression with a pound # modifier.

What does \\# mean in a regular expression? What does the # mean in a regul

Answer 1

As you have suspected, it's just a mistake.

To be sure, I ran:

String quote = Pattern.quote("_#_");

and the output was:

"\Q_#_\E"

So, clearly, the pound symbol ("#") is not a special character for java regex.

See: Pattern.quote()

Answer 2

I just had this same issue. It turned out that the prior programmer "missed" when changing all the "old code" from # to | and it was a simple mistake. I found this by checking all other code in the app and found NO other # symbols, but many similar areas of code with | included. And the | was right next to the # in this code. So someone was swapping out old regex for new regex and "missed".

Answer 3

\# is not a valid regex modifier. It would technically be a way to escape a # character, IF the # meant anything significant in Java's regex. Because it doesn't, Java is just ignoring this invalidity and reading it as a # instead of throwing you an error.