AHK Regex capture groups

Question

I am trying to get RegExReplace to work for me, and I encounter a strange behavior: 
 
 MyString := "This is a little test. Why not?" 
 MyResult := RegExReplace(MyString, " (t.+)\.", "$1") 
 MsgBox, %MyResult% 
 This is the result: 
 
 This is the behavior I would have expected: 
 
 AHK's regex replacement seems to include all characters into the match that are not explicitly excluded by being in the Regex but outside a capture group. (Space (" ") and period (".") in this example.) Is that normal? Can I turn this off and make it behave like all other Regex engines? 
 It's fine for simple regular expressions like the above, but once it gets really complex I don't want to re-test all my expressions to see whether they work in AHK as well... 
 Does anybody have any experience with this in AHK? 
 Daniel 
 
 EDIT: I should have added that this is the way to make it work: 
 MyResult := RegExReplace(MyString, ".*(t.+)\..*", "$1") 
 I am not looking for the regular expression, I am wondering why AHK's Regex treatment is so unusual in this respect.

Jesús Prieto · Accepted Answer

Hi Daniel: 
 Why do you think the RegExReplace function should return just "test"? 
 I hope it helps if I underline the relevant characters and leave the remaining chars just to see where they are in the original string: 
 
 Original string: This is a little test. Why not? 
 Matched substring: This is a little test. Why not? 
 Capturing group: This is a little test . Why not? 
 
 The replace string is $1, ie, the capturing group: 
 
 Replace string: test 
 
 Think about this: The replace string will replace the matched substring in the original string. 
 
 Replaced string: This is a littletest Why not?

Jesús Prieto · Answer

The first regex does what it&rsquo;s supposed to do: 
 - it matches [space]test[dot] 
 - there&rsquo;s a capturing group: test 
 - it replaces the match with the capturing group, so in the end, it removes the initial space and the ending period. 
 PS. I don&rsquo;t get what you mean here: 
 Unknown said: AHK's regex replacement seems to include all characters into the match that are not explicitly excluded by being in the Regex but outside a capture group.

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AHK Regex capture groups

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