How to Trim a string

for example

Sub ert()
Dim s As String, txt As String
s = ActiveCell.Value
With CreateObject("VBScript.RegExp")
    .Pattern = "\$[0-9]+,?[0-9]+" ' .Pattern = "\$\d+,?\d+"
    If .Test(s) Then
        txt = .Execute(s)(0)
    End If
    MsgBox txt
End With
End Sub