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Dos Commands

Posted on 1998-09-15
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Last Modified: 2010-04-30
I want to execute this command from VB,
"del c:\temp\*.*"
How do i do this, is there a fn that allows me to execute a
dos command from within VB.
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Question by:Coates
3 Comments
 
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chewhoung earned 30 total points
ID: 1434936
Hi Coates,

Look for Shell function in the VB help.
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by:Coates
ID: 1434937
Ive used the shell function, but this gives me error 53, file not found even when files exist in the directory!

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Expert Comment

by:mark2150
ID: 1434938
Dir is an *internal* command to COMMAND.COM. Try it as:

SHELL( "C:\COMMAND.COM /C DIR C:\TEMP\*.* /-P > RESULT", 1)

This will give you a text file RESULT with the output from the DIR command.

The /C after COMMAND.COM tells the shell to exit when complete. You may want to make it more generic and use Environ$("comspec") to pull the location of COMMAND.COM out of the environment instead of hard coding it to C:\. The /-P switch prevents the DIR command from stalling if you have /P set at the system level.

The problem with the SHELL command is that it is an async process. There is no way to tell that it has completed execution. There is a M$ workaround that suspends your VB until the child completes:

'
' These data type declarations are required to support the obscure windows
' function to spawn a child task and wait for it to finish before continuing
'
Private Type STARTUPINFO
    cb As Long
    lpReserved As String
    lpDesktop As String
    lpTitle As String
    dwX As Long
    dwY As Long
    dwXSize As Long
    dwYSize As Long
    dwXCountChars As Long
    dwYCountChars As Long
    dwFillAttribute As Long
    dwFlags As Long
    wShowWindow As Integer
    cbReserved2 As Integer
    lpReserved2 As Long
    hStdInput As Long
    hStdOutput As Long
    hStdError As Long
End Type
'
Private Type PROCESS_INFORMATION
    hProcess As Long
    hThread As Long
    dwProcessID As Long
    dwThreadID As Long
End Type
'
Private Declare Function WaitForSingleObject Lib "kernel32" (ByVal hHandle As Long, _
    ByVal dwMilliseconds As Long) As Long
'
Private Declare Function CreateProcessA Lib "kernel32" ( _
    ByVal lpApplicationName As Long, _
    ByVal lpCommandLine As String, _
    ByVal lpProcessAttributes As Long, _
    ByVal lpThreadAttributes As Long, _
    ByVal bInheritHandles As Long, _
    ByVal dwCreationFlags As Long, _
    ByVal lpEnvironment As Long, _
    ByVal lpCurrentDirectory As Long, _
    lpStartupInfo As STARTUPINFO, _
    lpProcessInformation As PROCESS_INFORMATION) As Long
'
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long
'
Const NORMAL_PRIORITY_CLASS = &H20&
Const INFINITE = -1&
Public Sub ExecCmd(cmdline$)
'
' This executes an external windows program and waits for it to complete
'
Dim proc As PROCESS_INFORMATION
Dim start As STARTUPINFO
'
' Initialize the STARTUPINFO structure:
'
start.cb = Len(start)
'
' Start the shelled application
'
ret& = CreateProcessA(0&, cmdline$, 0&, 0&, 1&, NORMAL_PRIORITY_CLASS, 0&, 0&, start, proc)
'
' Wait for the shelled application to finish:
'
holdhere:
    DoEvents
    ret& = WaitForSingleObject(proc.hProcess, 5000)
    If ret& <> 0 Then GoTo holdhere
'
ret& = CloseHandle(proc.hProcess)
End Sub

The one drawback to ExecCmd is that you need to set the properties of the child to include RUN MINIMIZED and CLOSE ON EXIT to make it's operation invisible to the user.

M

PS Gimme da points! (grin)

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