Visual Basic for Applications:
Using regular expressions

How to:

To use regular expressions in VBA, you first need to enable the Microsoft VBScript Regular Expressions library. In the VBA editor, go to Tools -> References, then check Microsoft VBScript Regular Expressions 5.5.

Here’s a basic example to find if a pattern exists within a string:

Sub FindPattern()
    Dim regex As Object
    Set regex = CreateObject("VBScript.RegExp")

    With regex
        .Global = True
        .IgnoreCase = True
        .Pattern = "\bis\b"  ' Looks for the word "is"
    End With
    
    Dim testString As String
    testString = "This is a test string."
    
    If regex.Test(testString) Then
        MsgBox "Pattern found."
    Else
        MsgBox "Pattern not found."
    End If
End Sub

To replace a pattern in a string:

Sub ReplacePattern()
    Dim regex As Object, replacedString As String
    Set regex = CreateObject("VBScript.RegExp")
    
    With regex
        .Global = True
        .IgnoreCase = False
        .Pattern = "\s"  ' Matches any white space character
    End With
    
    replacedString = regex.Replace("This is a test string.", "_")
    MsgBox replacedString  ' Outputs: "This_is_a_test_string."
End Sub

Deep Dive

The inclusion of regular expressions in programming languages often traces back to Unix tools from the 1970s. VBA integrated regex through the VBScript Regular Expressions library, highlighting its significance in text processing tasks even in applications not typically associated with heavy text manipulation like Excel or Access.

Despite their power, regex in VBA can sometimes be less intuitive or performant compared to more modern implementations in languages such as Python or JavaScript. For example, Python’s re module offers extensive support for named groups and more sophisticated pattern-matching features, providing a cleaner and potentially more readable approach. However, when working within the VBA ecosystem, regular expressions remain an invaluable tool for tasks that require pattern matching or text manipulation. The efficiency trade-off is often negligible in light of the convenience and capabilities regex brings to the table when dealing with strings in Office applications.