VBA RegExp (Regular Expressions)

Regular expressions are used for Pattern Matching. Maybe one of the best answers I’ve seen in StackOverflow is this about Regular expressions, from user Portland Runner, but the topic can get as tricky as this answer show, epic!. Following are a series of procedures to perform Regular Expressions operations. You can work with “Early binding” (set a reference to Microsoft VBScript Regular Expressions 5.5) or with “Late binding” through objects.

Early binding

  • Press ALT+F11 to access to the VBE.
  • Select “Tools” from the top menu.
  • Select “References”, and  check the box of “Microsoft VBScript Regular Expressions 5.5” to include in your workbook.
  • Click “OK”

Patterns

Basic definitions: - Range.
  • E.g. a-z matches an lower case letters from a to z
  • E.g. 0-5 matches any number from 0 to 5
[] Match exactly one of the objects inside these brackets.
  • E.g. [a] matches the letter a
  • E.g. [abc] matches a single letter which can be a, b or c
  • E.g. [a-z] matches any single lower case letter of the alphabet.
() Groups different matches for return purposes. See examples below. {} Multiplier for repeated copies of pattern defined before it.
  • E.g. [a]{2} matches two consecutive lower case letter a: aa
  • E.g. [a]{1,3} matches at least one and up to three lower case letter a, aa, aaa
+ Match at least one, or more, of the pattern defined before it.
  • E.g. a+ will match consecutive a’s a, aa, aaa, and so on
? Match zero or one of the pattern defined before it.
  • E.g. Pattern may or may not be present but can only be matched one time.
  • E.g. [a-z]? matches empty string or any single lower case letter.
* Match zero or more of the pattern defined before it. – E.g. Wildcard for pattern that may or may not be present. – E.g. [a-z]* matches empty string or string of lower case letters. . Matches any character except newline \n
  • E.g. a. Matches a two character string starting with a and ending with anything except \n
| OR operator
  • E.g. a|b means either a or b can be matched.
  • E.g. red|white|orange matches exactly one of the colors.
^ NOT operator
  • E.g. [^0-9] character can not contain a number
  • E.g. [^aA] character can not be lower case a or upper case A
\ Escapes special character that follows (overrides above behavior)
  • E.g. \., \\, \(, \?, \$, \^
Anchoring Patterns: ^ Match must occur at start of string
  • E.g. ^a First character must be lower case letter a
  • E.g. ^[0-9] First character must be a number.
$ Match must occur at end of string
  • E.g. a$ Last character must be lower case letter a
Precedence table: 
Order  Name                Representation
1      Parentheses         ( )
2      Multipliers         ? + * {m,n} {m, n}?
3      Sequence & Anchors  abc ^ $
4      Alternation         |
Predefined Character Abbreviations: 
abr    same as       meaning
\d     [0-9]         Any single digit
\D     [^0-9]        Any single character that's not a digit
\w     [a-zA-Z0-9_]  Any word character
\W     [^a-zA-Z0-9_] Any non-word character
\s     [ \r\t\n\f]   Any space character
\S     [^ \r\t\n\f]  Any non-space character
\n     [\n]          New line
Example 1: Run as macro The following example macro looks at the value in cell A1 to see if the first 1 or 2 characters are digits. If so, they are removed and the rest of the string is displayed. If not, then a box appears telling you that no match is found. Cell A1 values of 12abc will return abc, value of 1abc will return abc, value of abc123 will return “Not Matched” because the digits were not at the start of the string. 
Private Sub simpleRegex()
    Dim strPattern As String: strPattern = "^[0-9]{1,2}"
    Dim strReplace As String: strReplace = ""
    'Dim regEx As New RegExp
    Dim regEx As Object: Set regEx = CreateObject("VBScript.RegExp")
    Dim strInput As String
    Dim Myrange As Excel.Range

    Set Myrange = ActiveSheet.Range("A1")

    If strPattern  "" Then
        strInput = Myrange.Value

        With regEx
            .Global = True
            .MultiLine = True
            .IgnoreCase = False
            .Pattern = strPattern
        End With

        If regEx.Test(strInput) Then
            MsgBox (regEx.Replace(strInput, strReplace))
        Else
            MsgBox ("Not matched")
        End If
    End If
    Set regEx = Nothing
End Sub
Example 2: Run as an in-cell function This example is the same as example 1 but is setup to run as an in-cell function. To use, change the code to this: 
Function simpleCellRegex(Myrange As Excel.Range) As String
    'Dim regEx As New RegExp
    Dim regEx As Object: Set regEx = CreateObject("VBScript.RegExp")
    Dim strPattern As String
    Dim strInput As String
    Dim strReplace As String
    Dim strOutput As String


    strPattern = "^[0-9]{1,3}"

    If strPattern  "" Then
        strInput = Myrange.Value
        strReplace = ""

        With regEx
            .Global = True
            .MultiLine = True
            .IgnoreCase = False
            .Pattern = strPattern
        End With

        If regEx.test(strInput) Then
            simpleCellRegex = regEx.Replace(strInput, strReplace)
        Else
            simpleCellRegex = "Not matched"
        End If
    End If
    Set regEx = Nothing
End Function
Place your strings (“12abc”) in cell A1. Enter this formula =simpleCellRegex(A1) in cell B1 and the result will be “abc”. q3RRC
Example 3: Loop Through Range This example is the same as example 1 but loops through a range of cells. 
Private Sub simpleRegex()
    Dim strPattern As String: strPattern = "^[0-9]{1,2}"
    Dim strReplace As String: strReplace = ""
    'Dim regEx As New RegExp
    Dim regEx As Object: Set regEx = CreateObject("VBScript.RegExp")
    Dim strInput As String
    Dim Myrange As Excel.Range

    Set Myrange = ActiveSheet.Range("A1:A5")

    For Each cell In Myrange
        If strPattern  "" Then
            strInput = cell.Value

            With regEx
                .Global = True
                .MultiLine = True
                .IgnoreCase = False
                .Pattern = strPattern
            End With

            If regEx.Test(strInput) Then
                MsgBox (regEx.Replace(strInput, strReplace))
            Else
                MsgBox ("Not matched")
            End If
        End If
    Next
    Set regEx = Nothing
End Sub
Example 4: Splitting apart different patterns This example loops through a range (A1, A2 & A3) and looks for a string starting with three digits followed by a single alpha character and then 4 numeric digits. The output splits apart the pattern matches into adjacent cells by using the (). $1 represents the first pattern matched within the first set of (). 
Private Sub splitUpRegexPattern()
    'Dim regEx As New RegExp
    Dim regEx As Object: Set regEx = CreateObject("VBScript.RegExp")
    Dim strPattern As String
    Dim strInput As String
    Dim Myrange As Excel.Range

    Set Myrange = ActiveSheet.Range("A1:A3")

    For Each C In Myrange
        strPattern = "(^[0-9]{3})([a-zA-Z])([0-9]{4})"

        If strPattern  "" Then
            strInput = C.Value

            With regEx
                .Global = True
                .MultiLine = True
                .IgnoreCase = False
                .Pattern = strPattern
            End With

            If regEx.test(strInput) Then
                C.Offset(0, 1) = regEx.Replace(strInput, "$1")
                C.Offset(0, 2) = regEx.Replace(strInput, "$2")
                C.Offset(0, 3) = regEx.Replace(strInput, "$3")
            Else
                C.Offset(0, 1) = "(Not matched)"
            End If
        End If
    Next
    Set regEx = Nothing
End Sub
Results: 9eCZ5
Additional Pattern Examples 
String   Regex Pattern                  Explanation
a1aaa    [a-zA-Z][0-9][a-zA-Z]{3}       Single alpha, single digit, three alpha characters
a1aaa    [a-zA-Z]?[0-9][a-zA-Z]{3}      May or may not have preceeding alpha character
a1aaa    [a-zA-Z][0-9][a-zA-Z]{0,3}     Single alpha, single digit, 0 to 3 alpha characters
a1aaa    [a-zA-Z][0-9][a-zA-Z]*         Single alpha, single digit, followed by any number of alpha characters

</i8>    \<\/[a-zA-Z][0-9]\>            Exact non-word character except any single alpha followed by any single digit
Finally, there is this version of an UDF to use Regular Expressions, on the same post answer as the one above: 
Function regex(strInput As String, matchPattern As String, Optional ByVal outputPattern As String = "$0") As Variant
    Dim inputRegexObj As New VBScript_RegExp_55.RegExp, outputRegexObj As New VBScript_RegExp_55.RegExp, outReplaceRegexObj As New VBScript_RegExp_55.RegExp
    Dim inputMatches As Object, replaceMatches As Object, replaceMatch As Object
    Dim replaceNumber As Integer

    With inputRegexObj
        .Global = True
        .MultiLine = True
        .IgnoreCase = False
        .Pattern = matchPattern
    End With
    With outputRegexObj
        .Global = True
        .MultiLine = True
        .IgnoreCase = False
        .Pattern = "\$(\d+)"
    End With
    With outReplaceRegexObj
        .Global = True
        .MultiLine = True
        .IgnoreCase = False
    End With

    Set inputMatches = inputRegexObj.Execute(strInput)
    If inputMatches.Count = 0 Then
        regex = False
    Else
        Set replaceMatches = outputRegexObj.Execute(outputPattern)
        For Each replaceMatch In replaceMatches
            replaceNumber = replaceMatch.SubMatches(0)
            outReplaceRegexObj.Pattern = "\$" & replaceNumber

            If replaceNumber = 0 Then
                outputPattern = outReplaceRegexObj.Replace(outputPattern, inputMatches(0).Value)
            Else
                If replaceNumber > inputMatches(0).SubMatches.Count Then
                    'regex = "A to high $ tag found. Largest allowed is $" & inputMatches(0).SubMatches.Count & "."
                    regex = CVErr(xlErrValue)
                    Exit Function
                Else
                    outputPattern = outReplaceRegexObj.Replace(outputPattern, inputMatches(0).SubMatches(replaceNumber - 1))
                End If
            End If
        Next
        regex = outputPattern
    End If
End Function
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