I hope you're not including me in that :-))
My wife not only thinks I'm perfect, she KNOWS it!

PS Did I mention I'm a hypnotist in my spare time :-))))

Jeff

<fx Little Britain>
"Look into my eyes. Don't look around my eyes, look into my eyes.
When I count to three you will realise your method is rubbish and
you will tell everyone how GREAT Jeff's method is... 1, 2, 3...!"

Andi,

All six methods here are less than 1 second.  The timer returns 0 for
each one.

Poseur, Sabaka, Helmut, Jeff, JGM, and Andi

Thanks for the discussion on this topic.  I have learned alot just
playing around with each of your suggestions.  I have put together six
solutions using some or all of your suggestions.  I suppose that I
would have to cast my lot for the method proposed by Poseur the OP, as
it would be the easiest to adapt to aditional conditions.  I will be
firmly hooked on this method once I learn a little more about it.

Sub CallStringCompare()
Dim MyString As String

MyString = InputBox("Enter a test string")
'Is the string in the form 123_456.doc?  With one or more numbers
'on each side of a single _ character.
MsgBox ("The string match is " & StrCompare1(MyString))
MsgBox ("The string match is " & StrCompare2(MyString))
MsgBox ("The string match is " & StrCompare3(MyString))
MsgBox ("The string match is " & StrCompare4(MyString))
MsgBox ("The string match is " & StrCompare5(MyString))
MsgBox ("The string match is " & StrCompare6 _
(MyString, "[0-9]{1,}_[0-9]{1,}.doc"))

End Sub
Function StrCompare1(MyString As String) As Boolean
Dim A, B, C As Boolean
Dim i, j As Long

If StrComp(Right(MyString, 4), ".doc", vbTextCompare) Then
Exit Function
End If
i = Len(MyString)
A = Not Left(MyString, i - 4) Like "*[!0-9_]*"
j = InStr(MyString, "_")
B = j <> 0 And j <> 1 And j <> i - 4
C = InStr(j + 1, MyString, "_") = 0
StrCompare1 = A And B And C
End Function
Function StrCompare2(MyString As String) As Boolean
Dim oChrNum, i, j, k As Long
Dim tmpString As String
Dim A, B As Boolean

If StrComp(Right(MyString, 4), ".doc", vbTextCompare) Then
Exit Function
End If
For i = 1 To Len(MyString) - 4
oChrNum = Asc(Mid(MyString, i, 1))
If oChrNum >= 48 And oChrNum <= 57 Or oChrNum = 95 Then
tmpString = tmpString + Chr(oChrNum)
End If
Next i
A = MyString = tmpString & ".doc"
j = InStr(MyString, "_")
k = InStr(j + 1, MyString, "_")
B = j <> 0 And j <> 1 And j <> Len(MyString) - 4 And k = 0
StrCompare2 = A And B

End Function
Function StrCompare3(MyString As String) As Boolean
Dim sCompare As String
Dim i, j As Long
Dim bUnderscore As Boolean

If StrComp(Right(MyString, 4), ".doc", vbTextCompare) Then
Exit Function
End If
sCompare = ""
bUnderscore = False
j = Len(MyString) - 4
For i = 1 To j
If Mid(MyString, i, 1) = "_" And i <> 1 And i <> j And _
bUnderscore = False Then
sCompare = sCompare + "_"
bUnderscore = True
Else
sCompare = sCompare + "[0-9]"
End If
Next
sCompare = sCompare + ".doc"
StrCompare3 = MyString Like sCompare And bUnderscore
End Function
Function StrCompare4(MyString As String) As Boolean
Dim i, j, k, oLen As Long

If StrComp(Right(MyString, 4), ".doc", vbTextCompare) Then
Exit Function
End If
oLen = Len(MyString) - 4
For i = 1 To oLen
j = Asc(Mid(MyString, i, 1))
If j = 95 Then
k = k + 1
If i = oLen Or i = 1 Or k > 1 Or k = 0 Then
Exit Function
End If
ElseIf j < 48 Or j > 57 Then Exit Function
End If
Next
StrCompare4 = True

End Function
Function StrCompare5(ByVal MyString As String) As Boolean
Dim i As Long
Dim oLen As Long
oLen = Len(MyString) - 4
If InStr(MyString, "_") = 1 Or _
InStr(MyString, "_") = oLen Then Exit Function
For i = 0 To 9
MyString = Replace(MyString, i, "")
Next
If StrComp(MyString, "_.doc", vbTextCompare) = 0 Then
StrCompare5 = True
End If
End Function
Function StrCompare6(MyString As String, Pattern As String) As Boolean
Dim rgX As VBScript_RegExp_55.RegExp
Set rgX = New VBScript_RegExp_55.RegExp
With rgX
.Pattern = Pattern
StrCompare6 = .Test(MyString)
End With
End Function