Question on the 'shell' command in VB6 [Visual Studio]

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From: Bu on 19 Jan 2008 17:59

Hello,
I want to run from a VB6 program an old DOS program.
The DOS program displays some information on the screen. One parameter
(filename) is given to the DOS program on the command line.
For this i use the VB6 'Shell' command with in a string: path/filename
of the DOS program, a pipe to a tempory file (to catch the screen
info), and the the filename.
After the program runs i can process the DOS screen information i
piped to the tempory file in the VB6 program.
Sometimes this works and sometimes not.
I believe the reason is that the DOS program has not finished yet
while the VB program carries on.
I am a little bit confused with the information given on the internet
about waiting to continue after the shell program has finished
executing.
Can somebody tell me how i can wait till the DOS program finishes?

From: MikeD on 19 Jan 2008 18:12

From: Bob Riemersma on 19 Jan 2008 21:13

Ahh, but what waits for the batch file to end?

No, I'd look for any of hundreds of articles on the web about "Shell and
wait" in VB, or the more advanced "Shell with Pipe" technique that allows
your VB program to interact with a command-line Standard I/O stream program
instead of redirecting output to a disk file.

The latter works, but doesn't permit interaction.

"MikeD" <nobody(a)nowhere.edu> wrote in message
news:e3H$CDvWIHA.5208(a)TK2MSFTNGP04.phx.gbl...
>
> Being a DOS program, I supposed what I'd do is create a batch file that
> runs the DOS program (and your VB app would run that batch file). In the
> batch file, use the Start command, which has a /wait parameter.
>
> If you provide more information/details, you might get a better
> answer/solution.
>
> --
> Mike
> Microsoft MVP Visual Basic

From: Bill Plenge on 20 Jan 2008 10:28

Bu wrote:
> Hello,
> I want to run from a VB6 program an old DOS program.
> The DOS program displays some information on the screen. One parameter
> (filename) is given to the DOS program on the command line.
> For this i use the VB6 'Shell' command with in a string: path/filename
> of the DOS program, a pipe to a tempory file (to catch the screen
> info), and the the filename.
> After the program runs i can process the DOS screen information i
> piped to the tempory file in the VB6 program.
> Sometimes this works and sometimes not.
> I believe the reason is that the DOS program has not finished yet
> while the VB program carries on.
> I am a little bit confused with the information given on the internet
> about waiting to continue after the shell program has finished
> executing.
> Can somebody tell me how i can wait till the DOS program finishes?

When you're producing an output file that you know the full path/name of,
one technique I've used successfully in the past is to attempt to open the
output file for input or binary access with exclusive rights. If the
attempt fails I know the program isn't finished creating it, so I pause a
bit then try it again. If the attempt succeeds I know the other program
finished its processing and just close it and continue on to with my codes
processing..

Hope this helps.

Best,
Bill

From: Ralph on 20 Jan 2008 10:59

"Bu" <si(a)si.si> wrote in message
news:n7v4p3hloldlkdm1egohf1l3ucf9jdbho6(a)4ax.com...
> Hello,
> I want to run from a VB6 program an old DOS program.
> The DOS program displays some information on the screen. One parameter
> (filename) is given to the DOS program on the command line.
> For this i use the VB6 'Shell' command with in a string: path/filename
> of the DOS program, a pipe to a tempory file (to catch the screen
> info), and the the filename.
> After the program runs i can process the DOS screen information i
> piped to the tempory file in the VB6 program.
> Sometimes this works and sometimes not.
> I believe the reason is that the DOS program has not finished yet
> while the VB program carries on.
> I am a little bit confused with the information given on the internet
> about waiting to continue after the shell program has finished
> executing.
> Can somebody tell me how i can wait till the DOS program finishes?
>

Just to add to the pile, you can also just wait for the file to become
available.

Private Const FILE_NOTIFY_CHANGE_ATTRIBUTES = &H4
Private Const FILE_NOTIFY_CHANGE_DIR_NAME = &H2
Private Const FILE_NOTIFY_CHANGE_FILE_NAME = &H1
Private Const FILE_NOTIFY_CHANGE_SIZE = &H8
Private Const FILE_NOTIFY_CHANGE_LAST_WRITE = &H10
Private Const FILE_NOTIFY_CHANGE_SECURITY = &H100
Private Const FILE_NOTIFY_CHANGE_ALL = &H4 Or &H2 Or &H1 Or &H8 Or &H10 Or
&H100
Private Declare Function FindFirstChangeNotification Lib "kernel32" Alias
"FindFirstChangeNotificationA" (ByVal lpPathName As String,
ByVal bWatchSubtree As Long,
ByVal dwNotifyFilter As Long) As Long
Private Declare Function FindCloseChangeNotification Lib "kernel32" (
ByVal hChangeHandle As Long) As Long
Private Declare Function FindNextChangeNotification Lib "kernel32" (
ByVal hChangeHandle As Long) As Long
Private Declare Function WaitForSingleObject Lib "kernel32" (
ByVal hHandle As Long,
ByVal dwMilliseconds As Long) As Long
Private Declare Function ResetEvent Lib "kernel32" (
ByVal hEvent As Long) As Long

Public Sub WaitForFileChange(ByVal sFolder as String,
Optional ByVal nFilter = FILE_NOTIFY_CHANGE_ALL,
Optional ByVal bSubDir As Boolean = TRUE,
Optional ByVal TimeOut As Long = -1)
Dim hHook As Long

' set the hook
hHook = FindFirstChangeNotification(sFolder, bSubDir, nFilter)
' wait for a strike
WaitForSingleObject hHook, TimeOut
' got it so put the rod away
FindCloseChangeNotification hHook
End Sub

IMHO, if the launched app is short-lived and the return relatively small,
use Bob's suggestions. If the app involves user intervention and may hang
around for awhile and the return requires a file use the above.

-ralph

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