Shell(String, AppWinStyle, Boolean, Int32) Method
Runs an executable program and returns an integer containing the program's process ID if it is still running.
public static int Shell (string PathName, Microsoft.VisualBasic.AppWinStyle Style = Microsoft.VisualBasic.AppWinStyle.MinimizedFocus, bool Wait = false, int Timeout = -1);
static member Shell : string * Microsoft.VisualBasic.AppWinStyle * bool * int -> int
Public Function Shell (PathName As String, Optional Style As AppWinStyle = Microsoft.VisualBasic.AppWinStyle.MinimizedFocus, Optional Wait As Boolean = false, Optional Timeout As Integer = -1) As Integer
String. Name of the program to execute, together with any required arguments and command-line switches.
PathName can also include the drive and the directory path or folder.
If you do not know the path to the program, you can use the GetFiles to locate it. For example, you can call
My.Computer.FileSystem.GetFiles("C:", True, "testFile.txt"), which returns the full path of every file named
testFile.txt anywhere on drive C:\.
AppWinStyle. A value chosen from the AppWinStyle specifying the style of the window in which the program is to run. If
Style is omitted,
AppWinStyle.MinimizedFocus, which starts the program minimized and with focus.
Boolean. A value indicating whether the
Shell function should wait for completion of the program. If
Wait is omitted,
Integer. The number of milliseconds to wait for completion if
Timeout is omitted,
Shell uses -1, which means there is no timeout and
Shell does not return until the program finishes. Therefore, if you omit
Timeout or set it to -1, it is possible that
Shell might never return control to your program.
An integer containing the program's process ID if it is still running. 0 if the program already finished executing.
Style is not within range 0 through 9, inclusive.
Shell cannot find the
The following example uses the
Shell function to run an application specified by the user. Specifying AppWinStyle.NormalFocus as the second argument opens the application in normal size and gives it the focus.
Dim procID As Integer ' Run calculator. procID = Shell("C:\Windows\system32\calc.exe", AppWinStyle.NormalFocus) ' The preceding path is for Windows XP. ' The Windows 2000 path is C:\WINNT\system32\calc.exe.
The return value of the
Shell function depends on whether the program named in
PathName is still executing when
Shell returns. If you set
True and the program finishes before the timeout expires,
Shell returns zero. If the timeout expires, or if you omit
Wait or set it to
Shell returns the process ID of the program. The process ID is a unique number that identifies the running program.
Failure to Start
Shell function cannot start the named program, a FileNotFoundException error occurs. This can happen, for example, when you attempt to run a 16-bit program, such as
command.com, from an application using System.Windows.Forms. For a workaround, you can run a 32-bit program that calls the desired 16-bit program. In the case of
command.com, you can run
cmd.exe as an alternative.
Waiting for Completion
By default, the
Shell function runs the program asynchronously. This means that a program started with the
Shell function might not finish executing before the statements following the
Shell function are executed. If you want to wait for the program to finish before you continue, set
Determining the Exit Code
A process can return an exit code when it terminates. However, you cannot use
Shell to retrieve this exit code, because
Shell returns zero if it waits for termination, and also because the process runs in a different object from
To retrieve the exit code from a process, you must write your own code to initiate the process and wait for termination. The following example shows how to initiate a process, wait for it to terminate, and retrieve its exit code.
Dim procID As Integer Dim newProc As Diagnostics.Process newProc = Diagnostics.Process.Start("C:\WINDOWS\NOTEPAD.EXE") procID = newProc.Id newProc.WaitForExit() Dim procEC As Integer = -1 If newProc.HasExited Then procEC = newProc.ExitCode End If MsgBox("Process with ID " & CStr(ProcID) & _ " terminated with exit code " & CStr(procEC))
Protecting the File Specification
You should always enclose the entire path and file specification in quotation marks, as the following example shows.
ID = Shell("""C:\Program Files\display.exe"" -a -q", , True, 100000)
Each pair of adjacent double quotation marks (
" ") within the string literal is interpreted as one double quotation character in the string. Therefore, the preceding example presents the following string to the
"C:\Program Files\display.exe" -a -q
If you did not have the path enclosed in quotation marks, Windows would look for a file called
Program.exe in the C:\ directory, instead of
display.exe in the C:\Program Files directory.
If you do not enclose the path and file specification in quotation marks, there is a security risk if the file name or a path node contains spaces. In the preceding example, the path node
\Program Files includes a space. If the specification were not inside quotation marks and a program named
Program.exe had been installed in C:\, for example by illicit tampering, Windows would execute it instead of