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Editorial Team
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Asked: 2026-05-24T09:21:06+00:00

i have the following code to validate my file name entered using regular expression

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i have the following code to validate my file name entered using regular expression validator
but even after enter correct file name format, its hitting error saying enter valid filename

<asp:TextBox ID="TxtFileName" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator ID="FileNameRegularExpressionValidator" runat="server"
   ErrorMessage="Enter valid FileName"
   ControlToValidate="TxtFileName"
   ValidationExpression="^(\\[a-z_\-\s0-9\.]+)+\.(txt|gif|pdf|doc|docx|xls|xlsx)$">
</asp:RegularExpressionValidator>
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1 Answer

  1. Editorial Team

    At the moment, your regex requires the filename to start with a backslash. Also, your filenames may only contain the lowercase form of letters. Is that intentional?

    Also, you’re repeating your repeated group, a surefire recipe to bring your server down to its knees with catastrophic backtracking once someone enters an invalid filename that’s more than a few characters long.

    Perhaps 

    ValidationExpression="(?i)^[\w\s0-9.-]+\.(txt|gif|pdf|doc|docx|xls|xlsx)$">

    would be more suitable?

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