Launch Invisible Processes
You don't have to launch a process in a visible window; sometimes you just want to run a process and retrieve the output. The following example changes to the System folder, and then runs a DOS dir command with the file specification "*.com" which gives you a directory listing of the files in that folder with a .com extension. On Windows XP, the command shell interpreter recognizes the "&&" operator as a command separator, so you can place multiple commands on a single line. The ">>" operator redirects output into a named file. In this case, the code pipes the
dir command results into the file "dirOutput.txt" in the path designated by the
Application.StartupPath property.
Dim myProcess As Process = New Process()
Dim s As String
Dim outfile As String = Application.StartupPath & _
"\dirOutput.txt"
' get the System path
Dim sysFolder As String = _
System.Environment.GetFolderPath _
(Environment.SpecialFolder.System)
' set the file name and the command line args
myProcess.StartInfo.FileName = "cmd.exe"
myProcess.StartInfo.Arguments = "/C cd " & _
sysFolder & " && dir *.com >> " & Chr(34) & _
outfile & Chr(34) & " && exit"
' start the process in a hidden window
myProcess.StartInfo.WindowStyle = _
ProcessWindowStyle.Hidden
myProcess.StartInfo.CreateNoWindow = True
myProcess.Start()
' if the process doesn't complete within
' 1 second, kill it
myProcess.WaitForExit(1000)
If Not myProcess.HasExited Then
myProcess.Kill()
End If
' display exit time and exit code
MessageBox.Show("The 'dir' command window was " & _]
"closed at: " & myProcess.ExitTime & "." & _
System.Environment.NewLine & "Exit Code: " & _
myProcess.ExitCode)
myProcess.Close()
The preceding code returns an
ExitCode value of zero (
0). To see an example of a non-zero
ExitCode, append an "X" or some other character to the System folder path to make it invalid. That causes an error, and the
ExitCode value will be different. Because a process with an error could potentially run forever, the code uses an overloaded
WaitForExit method that accepts a number of milliseconds to wait before returning control to the launching program. The preceding code waits for 1 second before ending the launched process by calling the
Kill method, which forces the process to exit. Check for the existence of the
dirOutput.txt file in your application's startup directory to see the results.
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