Reading Console Output to write out an error log VB - vb.net

Question

I am running some commands on computers and I would like to have them output a seperate text file if the command cannot run.
For Each strUserName As String In strLines
Dim ReplaceCommand As String = sCommand.Replace("*", strUserName).Replace("$$$", saveFileDialog3.FileName & ".txt").Replace("###", exeSearch)
Shell("cmd.exe /c" & ReplaceCommand, AppWinStyle.Hide, True, )
' If Command Cannot Execute, List Why and Move onto Next Command
Using swrr As New StreamWriter(File.Open(ErrorLog, FileMode.OpenOrCreate))
If Console.Readline = "blahblah" Then swrr.WriteLine("FAIL") Else swrr.WriteLine("PASS")
End Using
Next
Am I on the right track? I am getting an output to a text file but its just one line ans always says PASS.

Answer 1

Several things: you're creating a new StreamWriter every time you want to write a line to it, instead of creating one then just writing to it when you need to. You're still using shell which is really basic, and not really suited for what you need. You should really be using a process for this.
I've written a function for you to use to execute the process instead of using the shell, which will return the output from the command execution to the ConsoleOutput variable, which you can then check for output strings.
Lastly, you should be using String.Format instead of replace to create the correct string for the command to run. For example:
Dim FirstName As String = "Jay"
Dim Age As String = "twenty"
Dim Greeting As String = String.Format("Hello {0}, I know you're {1} years old", FirstName, Age)
' Greetings value would be "Hello Jay, I know you're twenty years old"
So tweak the below to suit, specifically the Args variable, USING THE STRING.FORMAT function :)
Sub DoWork()
Dim ConsoleOutput As String = String.Empty
Using swrr As New StreamWriter(ErrorLog, True)
For Each strUserName As String In StrLines
ConsoleOutput = GetCMDOuput(strUserName, saveFileDialog3.FileName, exeSearch)
' If Command Cannot Execute, List Why and Move onto Next Command
If ConsoleOutput = "blahblah" Then swrr.WriteLine("FAIL") Else swrr.WriteLine("PASS")
Next
End Using
End Sub
Function GetCMDOuput(ByVal strUserName As String, ByVal strFileName As String, ByVal strExeSearch As String) As String
Dim Args As String = String.Format("/c -paramzero {0} -paramone {1} -paramtwo {2}", strUserName, strFileName, strExeSearch)
Dim CMD As New Process
CMD.StartInfo.FileName = "cmd.exe"
CMD.StartInfo.Arguments = Args
CMD.StartInfo.UseShellExecute = False
CMD.StartInfo.RedirectStandardInput = True
CMD.StartInfo.RedirectStandardOutput = True
CMD.StartInfo.CreateNoWindow = True
CMD.Start()
Dim retval As String = CMD.StandardOutput.ReadToEnd
CMD.WaitForExit()
Return retval
End Function