Java regex how to match _, /, or /123?

Question

I have prepared this REGEX [_[/\\\d+]] to get either of below

• An underscore -> _

OR

• A forward slash followed by some numbers /123

So when I try to match below are the results

1. _ (Matches -> OK)

2. / (Matches -> OK)

3. /123 (Doesn't match -> Not OK)

What am I missing here?

Answer 1

You are using [ and ] which denotes a character class which will match any of the listed a single time. Using \d+ will match either a digit or a + char.

If you add a quantifier like + to the character class itself you will repeat any of the listed but you will not have the OR logic.

You should use a pipe | for the OR part which will match either an underscore OR a forward slash followed by 1+ digits.

To also match a single forward slash you could match 0+ digits using the * instead of +

_|/\d+

regex demo

Note to double escape the backslash in Java _|/\\d+

Answer 2

Use: _|\\d*

Explanation:

  _     # an underscore
|       # OR
  /     # a slash
  \\d*  # 0 or more digits

Answer 3

You can simply use the pattern: _|/\\d*

The | essentially combines two separate patterns into one, and will match if either side matches.

This will match:

• _
• /
• /1
• /12
• /123 etc.

Answer 4

If i understood right your question you want either:

• one underscore
• or a slash followed by one or more digits

Here my solution:

_|(/\\d+)

Meaning:

• _ : underscore
• | : or
• ( : beginning of capturing group
• \\d : digit
• + : one or more times
• ) : endof capturing group

Hope this helps!