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

Accepted answer +26 upvotes

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