How do I get regex support in excel via a function, or custom function?

Question

It appears that regex (as in regular expressions) is not supported in excel, except via VBA. Is this so, and if it is, are there any \"open source\" custom VBA functions tha

Answer 1

Nothing built into Excel. VBScript has built-in support and can be called from VBA. More info available here. You can call the object using late binding in VBA. I've included a few functions that I put together recently. Please note that these are not well-tested and may have some bugs, but they are pretty straightforward.

This should at least get you started:

'---------------------------------------------------------------------------------------vv
' Procedure : RegEx
' Author    : Mike
' Date      : 9/1/2010
' Purpose   : Perform a regular expression search on a string and return the first match
'               or the null string if no matches are found.
' Usage     : If Len(RegEx("\d{1,2}[/-]\d{1,2}[/-]\d{2,4}", txt)) = 0 Then MsgBox "No date in " & txt
'           : TheDate = RegEx("\d{1,2}[/-]\d{1,2}[/-]\d{2,4}", txt)
'           : CUSIP = Regex("[A-Za-z0-9]{8}[0-9]",txt)
'---------------------------------------------------------------------------------------
'^^
Function RegEx(Pattern As String, TextToSearch As String) As String 'vv
    Dim RE As Object, REMatches As Object

    Set RE = CreateObject("vbscript.regexp")
    With RE
        .MultiLine = False
        .Global = False
        .IgnoreCase = False
        .Pattern = Pattern
    End With

    Set REMatches = RE.Execute(TextToSearch)
    If REMatches.Count > 0 Then
        RegEx = REMatches(0)
    Else
        RegEx = vbNullString
    End If
End Function '^^

'---------------------------------------------------------------------------------------
' Procedure : RegExReplace
' Author    : Mike
' Date      : 11/4/2010
' Purpose   : Attempts to replace text in the TextToSearch with text and back references
'               from the ReplacePattern for any matches found using SearchPattern.
' Notes     - If no matches are found, TextToSearch is returned unaltered.  To get
'               specific info from a string, use RegExExtract instead.
' Usage     : ?RegExReplace("(.*)(\d{3})[\)\s.-](\d{3})[\s.-](\d{4})(.*)", "My phone # is 570.555.1234.", "$1($2)$3-$4$5")
'             My phone # is (570)555-1234.
'---------------------------------------------------------------------------------------
'
Function RegExReplace(SearchPattern As String, TextToSearch As String, ReplacePattern As String, _
                      Optional GlobalReplace As Boolean = True, _
                      Optional IgnoreCase As Boolean = False, _
                      Optional MultiLine As Boolean = False) As String
Dim RE As Object

    Set RE = CreateObject("vbscript.regexp")
    With RE
        .MultiLine = MultiLine
        .Global = GlobalReplace
        .IgnoreCase = IgnoreCase
        .Pattern = SearchPattern
    End With

    RegExReplace = RE.Replace(TextToSearch, ReplacePattern)
End Function

'---------------------------------------------------------------------------------------
' Procedure : RegExExtract
' Author    : Mike
' Date      : 11/4/2010
' Purpose   : Extracts specific information from a string.  Returns empty string if not found.
' Usage     : ?RegExExtract("(.*)(\d{3})[\)\s.-](\d{3})[\s.-](\d{4})(.*)", "My phone # is 570.555.1234.", "$2$3$4")
'             5705551234
'             ?RegExExtract("(.*)(\d{3})[\)\s.-](\d{3})[\s.-](\d{4})(.*)", "My name is Mike.", "$2$3$4")
'
'             ?RegExReplace("(.*)(\d{3})[\)\s.-](\d{3})[\s.-](\d{4})(.*)", "My name is Mike.", "$2$3$4")
'             My name is Mike.
'---------------------------------------------------------------------------------------
'
Function RegExExtract(SearchPattern As String, TextToSearch As String, PatternToExtract As String, _
                      Optional GlobalReplace As Boolean = True, _
                      Optional IgnoreCase As Boolean = False, _
                      Optional MultiLine As Boolean = False) As String
Dim MatchFound As Boolean

    MatchFound = Len(RegEx(SearchPattern, TextToSearch)) > 0
    If MatchFound Then
        RegExExtract = RegExReplace(SearchPattern, TextToSearch, PatternToExtract, _
                                    GlobalReplace, IgnoreCase, MultiLine)
    Else
        RegExExtract = vbNullString
    End If
End Function