Multiline Regex Matching

[Empyreal]

I've been working with Regex and I've run into something that doesn't make sense to me; I either misunderstood how the Multiline option works, I'm not using it right, or it really just doesn't work like it's supposed to. This is a little test I made:

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    Dim TestString As String = "test" & vbNewLine & "sweet"
    Dim TestRegex As String = "^[a-z]*$"
    Dim ResultsString As String = String.Empty
    For Each StringMatch In System.Text.RegularExpressions.Regex.Matches(TestString, TestRegex, _
                                                                             System.Text.RegularExpressions.RegexOptions.Multiline)
        ResultsString &= StringMatch
    Next
 
    Console.WriteLine(resultsstring)
End Sub

The problem is, the only match that is found is the last line (in this case "sweet"). Why is this?

[.paul.]

try this:

Dim TestRegex As String = "^([a-z]|\r\n)*$"

[Empyreal]

If this was my string:

"oneword
twoword
threeword"

Your regex would return the following matches:

(0)"oneword
twoword
threeword"

I'd rather it return:

(0)"oneword"
(1)"twoword"
(2)"threeword"

My program has a checkbox so the user can decide whether or not they want the multiline option to be on/off; I could just split the text in the textbox at "\n" and put it into an array, then evaluate each string in the array when the user has checked the checkbox, but this would be a lot more complicated than just including/not including the multiline option.

Edit: More coherent/understandable now (hopefully) =P

[Empyreal]

Bump

[BadgerBadger]

You can just use the Split method to separate each line in the textbox, if that's what you're trying to do.

[Empyreal]

I could just split the text in the textbox at "\n" and put it into an array, then evaluate each string in the array when the user has checked the checkbox, but this would be a lot more complicated than just including/not including the multiline option.

I could do that, but, to my understanding, that's exactly what the multiline option does, so why go through all that trouble?

[BadgerBadger]

Oh yeah, but why the trouble trying to do the same with RegEx?

Also, you can grab specific lines using:

MessageBox.Show(TextBox1.Lines(2)) 'shows 3rd line

EDIT: or are you on about the multiline option in the RegEx class and not the textbox?

[Empyreal]

I'm talking about the multiline option in the regex class. Sorry, should have been more specific but I forgot all about the multiline property of the textbox =P

Anyway, I'm not trying to use regex JUST to split the text into lines; I was just using simple examples.

[BadgerBadger]

Ah, OK. Sorry, I should have realised.

So what is the actual issue?
You may want to test your expressions with this as it has a multiline feature:
http://gskinner.com/RegExr/

Sorry I couldn't be much help.

[Empyreal]

Thanks for that site; I'll actually probably use that a lot now =P

I set up a simple test to compare that site to Vb.net:

Regex: "^[a-z]*$"

Text:
"testone
testtwo
testthree"

Options: Multiline

The site returned three matches:
(0) testone
(1) testtwo
(2) testthree

Vb.net returned one match:
(0) testthree

[Pradeep1210]

Remove that $ from the end and it will work.

Regex: ^[a-z]*

[Empyreal]

Your right; it did work. But why?

[Pradeep1210]

I suspect that's because the * (star) matches anything except the newline character.

[Empyreal]

No, that's the period (.). The star (*) matches the character(s) preceding it 0 or more times.

I.e. "[a-z]*" would match "a", "abfds", "asdlfkdjalskfjasladfgklad", and so on.

[Pradeep1210]

That's right... but upto what point would it go? It would breakoff at newline character, Isn't it?

[Empyreal]

Well, yes it wouldn't match the newline character, but isn't that what the "$" does?

[Pradeep1210]

$ = match end of string

[Pradeep1210]

http://msdn.microsoft.com/en-us/library/az24scfc.aspx

[Empyreal]

The match must occur at the end of the string or before \n at the end of the line or string.

http://www.regular-expressions.info/anchors.html
Above is another site with a really good explanation of anchors. Look at the "Using ^ and $ as Start of Line and End of Line Anchors" section.