Some Basic Regex group Capture / Non-Capture Questions Topic is solved

[A_Perry_1984]

I am still relatively new to Regular Expressions.

Can somebody please demonstrate how to use a non-capture group in a function. For example:

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String := "Hello World"

I know that if I use the following:

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var := RegexReplace(string, "(Hello)/s(World)","$2")

Result: "World"... Easy-Peasy, but suppose I want to use a non-capture group. I am confused as how to make it work. I want to capture "World" by ignoring "Hello". So far I tried:

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pos := RegexMatch(string, "(?:Hello/s)World)", var) ;?: as in ignore "Hello"

Nevertheless, the result is still "Hello World". So what am I doing wrong here?

[A_AhkUser]

Regexes are not my cup of tea - far from it: someone might be able to clarify in details if needed. Anyway, It depends what you have in mind by 'by ignoring "Hello"' - here's some examples that come to my mind:

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string := "Hello World"
pos := RegExMatch(string, "(Hello)\s(World)", var)
MsgBox % pos "," var2
pos := RegexMatch(string, "(?:Hello)\s(World)", va)
MsgBox % pos "," va1
pos := RegexMatch(string, "Hello\s\KWorld", v) ;  \K causes any previously-matched characters to be omitted from the final matched string (here the whole string).
MsgBox % pos "," v

Btw its \s (backslash character).

Hope this helps.

[StefOnSteroids]

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String := "Hello World"
MsgBox, % RegExReplace(String, "(Hello\s)(World)", "$1")
MsgBox, % RegExReplace(String, "(?:Hello\s)(World)", "$1")

Both messages return the first group.
And yet, the first "captured" group in the second example is "World" and not "Hello ", because the first group does not even count as group 1. It is not "captured" at all.

[Klarion]

I do not care whatever you have in your mind about Capture/Non-Capture, just enjoy..

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_ := "Hello World"
RegExMatch(_, "(?<=Hello )World", x)
MsgBox % ""
.  x "`n"
.  RegExReplace(_, "Hello (?=World)")

and make all your previous help post with Green Check if you found a good answer (of course including this one)

[jeeswg]

See \K and (?<=...) [look-behind], mentioned here:
Regular Expressions (RegEx) - Quick Reference | AutoHotkey
https://autohotkey.com/docs/misc/RegEx-QuickRef.htm

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string := "Hello World"
pos := RegExMatch(string, "Hello\s\KWorld", var)
MsgBox, % pos "," var
pos := RegExMatch(string, "(?<=Hello\s)World", var)
MsgBox, % pos "," var

[A_Perry_1984]

It seems to me, in light of look aheads, behinds, and groups, there is really no purpose to a non-capture group. For that matter I'm not sure they do anything in AHK to begin with. Thank you everyone! These are so helpful.

[swagfag]

well they exist so there certainly must be some kind of a purpose to them. for example, they can be repeated, unlike lookaheads

[jeeswg]

Sometimes you need to use parentheses to contain something, e.g. (abc|def|ghi), but, by doing that, that would interfere with the indexes of any other numbered subpatterns.

A fix is to use ?:, e.g. (?:abc|def|ghi).

I hardly ever use it, the only example I could think of was when identifying variables: "(?:[_A-Za-z]|[^[:ascii:]])(?:\w|[^[:ascii:]]){0,252}".

[Klarion]

Good
I like the Green Check Mark

and
some of RegEx contents are not really needed for the beginner level
each level has its own ways of solving problem

ah, I am at the beginner level. Do not misunderstand me.

Good Luck To You

[A_Perry_1984]

Sometimes you need to use parentheses to contain something, e.g. (abc|def|ghi), but, by doing that, that would interfere with the indexes of any other numbered subpatterns.

A fix is to use ?:, e.g. (?:abc|def|ghi).

I hardly ever use it, the only example I could think of was when identifying variables: "(?:[_A-Za-z]|[^[:ascii:]])(?:\w|[^[:ascii:]]){0,252}".

I see your point. I don't think that would something needed very often.

[A_Perry_1984]

Good
I like the Green Check Mark

and
some of RegEx contents are not really needed for the beginner level
each level has its own ways of solving problem

ah, I am at the beginner level. Do not misunderstand me.

Good Luck To You

No worries. I get what your saying. I don't think regex is that complicated to learn, so much as figuring out the limitless ways to manipulate text with it.