I recently worked on a project that required updating a specific line of text in a file. This proved to be surprisingly difficult because I’ve never done that in ASP.NET before and I could not find any sample code on the Internet. You cannot write to a file after opening it to read through the lines of text. I had to write to a temporary file, delete the original file, and then copy the temporary file with the original file name. A line counter is used to update the target line within the file. I created a generic version of this code for my notes:<\/p>\n
<%@ Import Namespace="System" %><\/b><\/font>\r\n<%@ Import Namespace="System.IO" %><\/b><\/font>\r\n<<\/font>html<\/font>><\/font>\r\n<<\/font>title<\/font>><\/font>Update Text File<\/<\/font>title<\/font>><\/font>\r\n<<\/font>script<\/font> language="vb" runat="server"><\/font>\r\n' requires ASPNET account to have write permissions on target directory<\/font>\r\nPrivate<\/font> Sub<\/font> btnUpdate_Click(o As<\/font> Object, e As<\/font> EventArgs)\r\n Try<\/font>\r\n Dim<\/font> w As<\/font> StreamWriter\r\n w = File.CreateText("C:\/Inetpub\/wwwroot\/experiments\/temp.txt")\r\n Dim<\/font> r As<\/font> StreamReader = File.OpenText("C:\/Inetpub\/wwwroot\/experiments\/test.txt")\r\n Dim<\/font> intLineCount As<\/font> Integer<\/font>\r\n Dim<\/font> strTextLine As<\/font> String<\/font>\r\n Dim<\/font> strTodaysDate As<\/font> String<\/font>\r\n \r\n intLineCount = 0\r\n While<\/font> r.Peek() <> -1\r\n strTextLine = r.ReadLine()\r\n intLineCount = intLineCount + 1\r\n ' update the 5th line<\/font>\r\n If<\/font> intLineCount = 5 Then<\/font>\r\n strTodaysDate = Now()\r\n w.WriteLine(strTodaysDate)\r\n Else<\/font>\r\n w.WriteLine(strTextLine)\r\n End If<\/font>\r\n End While<\/font>\r\n \r\n w.Close()\r\n r.Close()\r\n \r\n Dim<\/font> f As<\/font> File\r\n ' delete original file<\/font>\r\n f.Delete("C:\/Inetpub\/wwwroot\/experiments\/test.txt")\r\n ' copy the temp file to restore deleted file<\/font>\r\n f.Copy("C:\/Inetpub\/wwwroot\/experiments\/temp.txt", "C:\/Inetpub\/wwwroot\/experiments\/test.txt")\r\n \r\n lblMessage.Text = "File Updated!"\r\n Catch<\/font> ex As<\/font> Exception\r\n lblMessage.Text = ex.Message & "<br>" & ex.Source & "<br>" & ex.StackTrace & "<br>"\r\n End Try<\/font>\r\nEnd Sub<\/font>\r\n<\/<\/font>script<\/font>><\/font>\r\n<<\/font>body<\/font>><\/font>\r\n<<\/font>h1<\/font> style="font-family:Arial"><\/font>Update Text File<\/<\/font>h1<\/font>><\/font>\r\n<<\/font>hr<\/font> size="1" noshade><\/font>\r\n<<\/font>form<\/font> runat="server" id="form1" name="form1"><\/font>\r\n<asp:button id="btnUpdate" text="Update File" runat="server" onclick="btnUpdate_Click"><\/asp:button><\/b><\/font>\r\n<<\/font>br<\/font>><<\/font>br<\/font>><\/font>\r\n<<\/font>font<\/font> face="Arial"><asp:label id="lblMessage" runat="server" \/><\/font<\/font>><\/b><\/font>\r\n<\/<\/font>form<\/font>><\/font>\r\n<\/<\/font>body<\/font>><\/font>\r\n<\/<\/font>html<\/font>><\/font><\/pre>\nNOTE:<\/strong> Due to some problems with WordPress I had to replace backslashes with forward slashes in the file paths.<\/p>\n","protected":false},"excerpt":{"rendered":"I recently worked on a project that required updating a specific line of text in a file. This proved to be surprisingly difficult because I’ve never done that in ASP.NET before and I could not find any sample code on … Continue reading