Regex for matching HashTags in any language

I have a field in my application where users can enter a hashtag. I want to validate their entry and make sure they enter what would be a proper HashTag. It can be in any language and it should NOT precede with the # sign. I am writing in JavaScript.

So the following are GOOD examples:

• Abcde45454_fgfgfg (good because: only letters, numbers and _)
• 2014_is-the-year (good because: only letters, numbers, _ and -)
• בר_רפאלי (good because: only letters and _)
• арбуз (good because: only letters)

And the following are BAD examples:

• Dan Brown (Bad because has a space)
• OMG!!!!! (Bad because has !)
• בר רפ@לי (Bad because has @ and a space)

We had a regex that matched only a-zA-Z0-9, we needed to add language support so we changed it to ignore white spaces and forgot to ignore special characters, so here I am.

Some other StackOverflow examples I saw but didn't work for me:

1. Other languges don't work
2. Again, English only

[edit]

• Added explanation why bad is bad and good is good
• I don't want a preceding # character, but if I would to add a # in the beginning, it should be a valid hashtag
  • Basically I don't want to allow any special characters like !@#$%^&*()=+./,[{]};:'"?><

If your disallowed characters list is thorough (!@#$%^&*()=+./,[{]};:'"?><), then the regex is:

^#?[^\s!@#$%^&*()=+./,\[{\]};:'"?><]+$

Demo

This allows an optional leading # sign: #?. It disallows the special characters using a negative character class. I just added \s to the list (spaces), and also I escaped [ and ].

Unfortunately, you can't use constructs like \p{P} (Unicode punctuation) in JavaScript's regexes, so you basically have to blacklist characters or take a different approach if the regex solution isn't good enough for your needs.