The _SHELL system memory variable is used to prevent access to the Command window while a program is running in Visual FoxPro. The DO command with the name of a program to execute is usually stored to _SHELL.

You can also specify a command to execute when Visual FoxPro is started by placing the SHELL configuration item in your Visual FoxPro configuration file.

The following example demonstrates how _SHELL typically can be used.

1. A startup program named Mystart.prg is used to launch another program named Myapp.prg. Mystart.prg stores the command to run Myapp.prg to _SHELL. This starts Myapp.prg. Before Visual FoxPro displays the Command window, _SHELL is checked for a command. If _SHELL contains a command, it is executed and Visual FoxPro then stores the empty string to _SHELL.

2. After the initialization code in Myapp.prg is successfully executed, the command to launch Myapp.prg is stored again to _SHELL. Visual FoxPro does not execute the command or store the empty string to _SHELL, and access to the Command window is prevented. (The Command window cannot be accessed when _SHELL contains anything but the empty string).

3. Before Myapp.prg finishes execution, it stores the empty string to _SHELL to restore access to the Command window.

   	Copy Code
   *** MYSTART.PRG *** ... _SHELL = "DO MYAPP.PRG" *** MYAPP.PRG *** *** Initialization Code *** ... *** Initialization Code successfully completed? *** _SHELL = "DO MYAPP.PRG" && Prevents access to Command window ... *** Clean up Code *** _SHELL = ""

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