File Exists? with user entry

I have a textbox where the user can browse for a file or type the filename in the textbox. If the user types the filename, how do I check to see if that file exists or not?

Code:

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If Dir$("MyFileName") <> "" Then
    'File exists
Else
    'File does not exist.
End If

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For user input:

Code:

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Private Sub Command1_Click()
Dim file As String
file = InputBox("What file do you want to check?")
If file <> "" Then
If Dir$(file) <> "" Then
    'File exists
Else
    'File does not exist.
End If
End If
End Sub

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How do you check if a directory exists? Thanks.

If Dir$(Mydirectory,vbDirectory) <> "" Then 'that directory exists