Script hangs when reading output of command inside vbscript

Question

Following code hangs  after the line "4 Go" but only on windows 2003.
Set objShell = CreateObject("WScript.Shell")
wscript.echo "2 Go"
backupstate = "wmic PATH WIN32_SERVICE where (name='vss') GET state"
wscript.echo "3 Go"
Set objExecObject = objShell.Exec(backupstate)
wscript.echo "4 Go"
With objExecObject
Do While .Status=0
Wscript.Sleep 10
Do While Not .StdOut.AtEndOfStream
strText = .StdOut.ReadLine()
If Not .StdErr.AtEndOfStream Then
.StdErr.ReadLine
End If
Loop
Loop
End With
Same code works perfectly fine on Windows 2008 and above.
Any suggestion?
-KAKA-

Answer 1

Your script hangs (or more precisely: it keeps looping) because the Exec method of of the Shell object is notoriously unreliable when it comes to detecting the status of the executable it invokes. You can easily find out by placing the line
wscript.echo "Status=" & objExecObject.status
inside your loop. This only works properly if you run the script with cscript.exe.
As Frederik says. :)
To explicitly answer why that MSKB article suggests continually emptying the error buffer, it's because doing so is better than
not doing so.
Another workaround I use in preference to embedding the console tool within a WSH script is to factor out the tool so I don't have to manipulate it internally; instead I pipe the output in to the script.
For example, suppose your script is named ProcessWmicOutput.vbs. within the script you would do something like this:
data = WScript.Stdin.ReadAll
to get all the data from wmic into a variable named data . Alternatively, you would do something like this, line by line (I'm making the script just relay StdOut from wmic):
Do While Not WScript.StdIn.AtEndOfStream
WScript.StdOut.WriteLine WScript.StdIn.ReadLine()
Loop
To run the script, getting wmic data, you would do this at a command prompt:
wmic PATH WIN32_SERVICE where (name='vss') GET state | cscript ProcessWmicOutput.vbs