VB.NetSystem Objects

VB.Net - RegEx

RegEx

RegEx is a language used for string manipulation.

To me, RegEx has always been hard, but the alternatives are harder ;^).

My advise is, When you play with RegEx, do a lot of testing. Especially test strings with multiple copies of the expression you are looking for.

Replace with RegEx

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imports system.text.regularexpressions

dim ps as string
ps=Regex.replace(sz, "____\r\n", "<hr>")

ps=regex.replace(sz, "\+B\+", "<B>")

Replace has 3 arguments

  • the string we want to play with
  • the characters we want to find within the string
  • the characters that will be converted

The first replace function above replaces 4 underscores (and a linefeed) with an <hr> tag.
The second replace function replaces plus B plus with a <b> tag.

The second and third arguments could contain regular expressions. Here are a few things to note.

  • The backslash character is used by the expression function.
  • \r means carriage return.
  • \n means linefeed.
  • The plus character is also used by the expression function. Since we need that we can prefix it with a \ character to indicate that’s a character we really want.

Another form of the replace function goes like this

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ParsedText = Regex.Replace(ParsedText, _
    "\[\[FORM.*\]\]", AddressOf aFormTag)

This will call a function called aFormTag which could resemble the following:

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Public Shared Function aFormTag(ByVal m As Match) As String
    '                 0              1     2
    ' converts [ [FORM:Missing Person|EMAIL|mark at thecoffeeplace.com]] 
    ' into a submit button
    Dim sz As String = ""

    Dim tag As String = m.Value
    If Left(tag, 2) = "[[" Then
        tag = Mid(tag, 8, Len(tag)) ' strip off [[Form
    End If
    If Right(tag, 2) = "]]" Then
         tag = Mid(tag, 1, Len(tag) - 2) ' strip off ]]
    End If
    Dim args() As String  = tag.Split("|")

    sz = "<input type='Hidden' name='FormType' value='" & args(1).ToUpper & "'>" & vbCrLf _
        & "<input type='button' " _
            & "value='" & args(0) & "' " _
            & "OnClick='btnSubmitIt__Click()'>" & vbCrLf
    Return sz
End Function

\d{1,3} –> 1 to 3 digits