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  1. import java.util.*;
  2. import java.util.regex.*;
  3.  
  4. class Ideone
  5. {
  6. 	public static void main (String[] args) throws java.lang.Exception
  7. 	{
  8. 		String fileName = "20210101-000000_first_second_1234.csv";
  9. 		Pattern pattern = Pattern.compile("\\d{4}(?=\\.[^.]+$)");
  10. 		Matcher m = pattern.matcher(fileName);
  11. 		if (m.find()) {
  12. 			System.out.println(m.group());
  13. 		}
  14. 	}
  15. }
Success #stdin #stdout 0.08s 40324KB
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Standard input is empty
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1234
https://ideone.com/8goDvy
language:
Java (HotSpot 12)
created:
2 years ago
visibility:
secret

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