正则表达式匹配特定单词之前的确切短语

Question

I would like to match any four digits occurring before double space and word "from" ex.

• 2356 from
• 1524 from
• 1223 from

The expression \\d{4} from extracts digits, double space and the word "from", but ideally I would like to get only those four digits (without the trailing spaces and word "from") and only in cases when they are not part of number with hyphen like this example:

• 2536 from = 2536
• 8574 from = 8574
• 35-6655 from = no match
• 3652 = no match (number without word "from" after the digits)

Answer 1

You need to use either grouping (...) operators in your regex:

(\d{4})  from

and then extract group #1 from the match. Or a zero-width look-ahead match using (?=...) .

\d{4}(?=  from)

To avoiding a match following the hyphen, you can use a zero-width negative look-behind.

(?<!-)\d{4}(?=  from)

Explanation:

(?<!_)_______________ negative zero-width look-behind ...
____-________________ ... doesn't match if a "-" is found
______\\d{4}__________ four digits
___________(?=______) positive zero-width look-ahead ...
______________ from_ ... matches if " from" is found

Answer 2

You can do by ([0-9]{4}) from

More see in here