Shell process' standard output reading in Visual Basic 6 - vb6

Question

First, let me say that I'm not a Visual Basic 6 expert...
My need is to:
launch from a VB6 client code an exeternal .exe file
wait for the process to finish and - during its execution - read the messages coming from its standard output "on the fly" (so that I can print it on a text-filed widget or similars).
I'm wondering if it is even possible to do that in VB6...after a long search on the Internet I didn't come up with anything. Found a lot of examples of how to use the Shell function, but it seems to force me to read the stdout all at once when the process' execution is over, but I want to poll the process for "fresh" messages as they become available.
Any code snippets/suggestions/references are really appreciated.
Thanks in advance!

Answer 1

Use CreatePipe() to create an anonymous pipe that you can pass to CreateProcess().
You can then read from this pipe as required (either using polling or overlapped/async I/O.
This should give you enough info to find a good example.

Answer 2

You can always use Exec method of WshShell to do the job.
I prefer to use a home-grown API based solution cExec.cls much simpler than Bob Riemersma's user control (but not as versatile).

Answer 3

You can also create a batch file that has all the commands that you need to run, and then from VB6 call the batch file by executing
Shell "C:\YourPath\BatchFileName.bat > OutputFileName.txt" 'Overwrites OutputFilename.txt everytime
once you execute that, then open OutputFileName.txt and you will find all of the messages and output that was generated during the batch process. You can then read it in VB6 in a simple open "filename" for input as #1
You should also notice that if you use double GreaterThan symbols, the the output file will not be overwritten every time the batch runs. Instead, it will get appended with the new lines of output.
Shell "C:\YourPath\BatchFileName.bat >> OutputFileName.txt" 'This will append to OutputFileName.txt

Answer 4

Here is the function you want. The exercise of declaring the API (CreatePipe, CreateProcessA, CloseHandle, etc), the types (PROCESS_INFORMATION, STARTUPINFO, SECURITY_ATTRIBUTES) the constants (STARTF_USESTDHANDLES, STARF_USESHOWWINDOW, etc) are left to the reader.
Public Function ExecuteCommand(ByVal CommandLine As String, Optional bShowWindow As Boolean = False, Optional sCurrentDir As String) As String
Dim proc As PROCESS_INFORMATION 'Process info filled by CreateProcessA
Dim ret As Long 'long variable for get the return value of the
'API functions
Dim start As STARTUPINFO 'StartUp Info passed to the CreateProceeeA
'function
Dim sa As SECURITY_ATTRIBUTES 'Security Attributes passeed to the
'CreateProcessA function
Dim hReadPipe As Long 'Read Pipe handle created by CreatePipe
Dim hWritePipe As Long 'Write Pite handle created by CreatePipe
Dim lngBytesRead As Long 'Amount of byte read from the Read Pipe handle
Dim strBuff As String * 256 'String buffer reading the Pipe
'if the parameter is not empty update the CommandLine property
If Len(CommandLine) > 0 Then
mCommand = CommandLine
End If
'if the command line is empty then exit whit a error message
If Len(mCommand) = 0 Then
ApplicationEventLogError "Command Line empty in procedure ExecuteCommand of module modPipedOutput."
Exit Function
End If
'Create the Pipe
sa.nLength = Len(sa)
sa.bInheritHandle = 1&
sa.lpSecurityDescriptor = 0&
ret = CreatePipe(hReadPipe, hWritePipe, sa, 0)
If ret = 0 Then
'If an error occur during the Pipe creation exit
Debug.Print "CreatePipe failed. Error: " & Err.LastDllError & " (" & ReturnError(Err.LastDllError)
Exit Function
End If
'Launch the command line application
start.cb = Len(start)
start.dwFlags = STARTF_USESTDHANDLES Or STARTF_USESHOWWINDOW
'set the StdOutput and the StdError output to the same Write Pipe handle
start.hStdOutput = hWritePipe
start.hStdError = hWritePipe
' start.hStdInput = hInReadPipe
If bShowWindow Then
start.wShowWindow = SW_SHOWNORMAL
Else
start.wShowWindow = SW_HIDE
End If
'Execute the command
If Len(sCurrentDir) = 0 Then
ret& = CreateProcessA(0&, mCommand, sa, sa, 1&, _
NORMAL_PRIORITY_CLASS, 0&, vbNullString, start, proc)
Else
ret& = CreateProcessA(0&, mCommand, sa, sa, 1&, _
NORMAL_PRIORITY_CLASS, 0&, sCurrentDir, start, proc)
End If
If ret <> 1 Then
'if the command is not found ....
Debug.Print "File or command not found in procedure ExecuteCommand"
Exit Function
End If
'Now We can ... must close the hWritePipe
ret = CloseHandle(hWritePipe)
' ret = CloseHandle(hInReadPipe)
mOutputs = vbNullString
'Read the ReadPipe handle
Do
ret = ReadFile(hReadPipe, strBuff, 256, lngBytesRead, 0&)
mOutputs = mOutputs & Left$(strBuff, lngBytesRead)
'Send data to the object via ReceiveOutputs event
Loop While ret <> 0
'Close the opened handles
Call CloseHandle(proc.hProcess)
Call CloseHandle(proc.hThread)
Call CloseHandle(hReadPipe)
'Return the Outputs property with the entire DOS output
ExecuteCommand = mOutputs
End Function