Regular Expression 2 : The rest Regex class

This is the second installment of Regular expressions in Scala. In the first installment the basics were shown and a few of the methods in the Regex class were inspected. This topic will look at the rest of the methods in the Regex class.

Regex.findPrefixMatchOf

1. /*
2. returns the match if the regex is the prefix of the string
3. */
4. scala> "(h)(e)|(l)".r findPrefixMatchOf "hello xyz"  
5. res2: Option[scala.util.matching.Regex.Match] = Some(he)
7. scala> "lo".r findPrefixMatchOf "hello xyz"  
8. res3: Option[scala.util.matching.Regex.Match] = None
10. /*
11. The method is essentially the same as adding the boundary regex character
12. */
13. scala> "^ab".r findFirstMatchIn "ababab"
14. res8: Option[scala.util.matching.Regex.Match] = Some(ab)
16. scala> "^ab".r findFirstMatchIn "hababab"
17. res9: Option[scala.util.matching.Regex.Match] = None
19. /*
20. findPrefixOf is the same but returns the matched string instead
21. */
22. scala> "ab".r findPrefixOf "haababab"       
23. res11: Option[String] = None
25. scala> "ab".r findPrefixOf "ababab"    
26. res12: Option[String] = Some(ab)

Regex.replaceAllIn -- Essentially the same as using String.replaceAll
Regex.replaceFirstIn -- Essentially the same as using String.replaceFirst

1. scala> "(h)(e)|(l)".r replaceAllIn ("hello xyz","__")
2. res13: String = ______o xyz
4. scala> "hello xyz" replaceAll ("(h)(e)|(l)","__")    
5. res14: java.lang.String = ______o xyz
7. scala> "hello xyz" replaceFirst ("(h)(e)|(l)","__")  
8. res16: java.lang.String = __llo xyz
10. scala> "(h)(e)|(l)".r replaceFirstIn ("hello xyz","__")
11. res17: String = __llo xyz

This next section is not Scala specific but because Regex does not provide a way to set the flags CASE_INSENSITIVE, DOTALL, etc... The section is useful to demonstrate how to do it as part of the standard regex syntax.

1. // examples based on java blog at: <a href="http://www.javaranch.com/journal/2003/04/RegexTutorial.htm#flags">http://www.javaranch.com/journal/2003/04/RegexTutorial.htm#flags</a>
2. scala> val input = """Hey, diddle, diddle,      
3.      | |The cat and the fiddle,                 
4.      | |The cow jumped over the moon.           
5.      | |The little dog laughed                  
6.      | |To see such sport,                      
7.      | |And the dish ran away with the spoon.""".stripMargin
8. input: String = 
9. Hey, diddle, diddle,
10. The cat and the fiddle,
11. The cow jumped over the moon.
12. The little dog laughed
13. To see such sport,
14. And the dish ran away with the spoon.
16. // by default regex is case sensitive
17. scala> """the \w+?(?=\W)""".r findAllIn input foreach (println _)
18. the fiddle
19. the moon
20. the dish
21. the spoon
23. /* the (?i)  makes the match case insensitive the complete set of options are:
24. (?idmsux)
25. • i - case insensitive
    • d - only unix lines are recognized as end of line
    • m - enable multiline mode
    • s - . matches any characters including line end
    • u - Enables Unicode-aware case folding
    • x - Permits whitespace and comments in pattern
26. */
27. scala> """(?i)the \w+?(?=\W)""".r findAllIn input foreach (println _)
28. The cat
29. the fiddle
30. The cow
31. the moon
32. The little
33. the dish
34. the spoon