Chapter 3: USING START TO OPEN FILES FROM FLASH APPLICATIONS

The EXEC command can be used to launch executable files like EXE and BAT files, and even older (DOS executable) COM files, but at some point a client is going to ask you to open a PDF file or even a text file. If you've tried this fscommand("exec", "file.txt") actionScript with EXEC you already know that it doesn't work. So what can you do?

The most commonly suggested solution is to use START to do it. Despite the fact that it appears to work, it isn't a very good idea.

If you go to any DOS prompt and type start file.pdf, Windows will figure out what application should be used to open the PDF file and launch it with the file name as an argument. The same thing happens if you just type the file name in the RUN dialog box from the Windows Start menu.

PLAY DEMO: » RUN/DOS Example
Disclaimer: Windows XP users need to manually find and install a Java Virtual Machine plug-in.

This is exactly what we need to open documents in Flash!

The problems begin when you try to call START from Flash. Under Windows 95, 98 and ME there is actually an external file called START.EXE that lives in the Windows\Command directory. Under Windows NT, 2000 and XP the start command is implemented as a command processor extension, and there is no START.EXE.

If you try to EXEC "START" or "START.EXE" on 95/98/ME it will work but on NT/2K/XP you'll get a dialog box like this one because START.EXE doesn't actually exist. Flash can only EXEC files, it doesn't know how to use command processor extensions.

But, there are ways around this. We can ask the command processor for help.

A BRIEF HISTORY OF COMMAND PROCESSORS...

What we call a DOS box today is actually a special program that was once the only interface between humans and their PCs. It existed only to process English-like commands into instructions to the operating system.

There are actually two different command processors around today command.com and cmd.exe. The command processor used by your system depends on which version of Windows you're using.

Win9x, and ME use command.com. The .com extension (instead of .exe) is a dead giveaway (for use old timers) that this is a 16-bit application, a holdover from the days of DOS and not a true 32-bit application. You can still find a copy of command.com on NT, 2000 and XP in \WinNT\System32 folder for backward compatibility.

Windows NT, 2000 and XP use cmd.exe. Although they look very similar when you run them, cmd.exe is a true 32-bit console mode application and is quite a bit more sophisticated than its 16-bit predecessor.

These two applications share a common heritage and CMD.EXE was designed to do everything that
command.com could do, just better. The common feature that interests us is the ability to process command line arguments. You pass arguments to the command processor using the /C switch like this:

command.com /C start file.pdf
cmd.exe /C start file.pdf

If you want to open a text file on 95/98/ME this will do the trick:

fscommand("exec", "command.com" + chr(9) + "/c" + chr(9) + "start" + chr(9)+ file.txt");

Although COMMAND.COM exists on NT/2K/XP, and you can launch it, it's just a copy of the 16-bit command processor. Since START is implemented as an extension to CMD.EXE on these systems, it doesn't work! So to use START on NT/2K/XP you have to do this:

fscommand("exec", "cmd.exe"+chr(9)+"/c"+chr(9)+"start"+chr(9)+"file.txt");

But, CMD.EXE only exists on NT/2K/XP so this is very platform specific. Unless you're willing to ask your users which system they're using (and assuming they know) this solution isn't very good. What we need is a way to call START that will work on all platforms. Luckily, DOS provides a mechanism to do this, BAT files and Flash can launch BAT files.

First we need to create a BAT file that can do what the START command does. That part is easy, just create a BAT file called DOSTART.BAT put the following line in it:

start %1

Now all we have to do is call the DOSTART.BAT file like this from Flash and it will work on any platform your user may have.

fscommand("exec", "dostart.bat"+chr(9)+"file.txt");

The only drawback with using BAT files is the ugly black DOS box that appears when you use them. You may have heard people mention using PIF files but they don't work on NT/2K/XP and the best result you can manage on 95/98/ME with a PIF file is to minimize the DOS box and make it appear in the Windows taskbar. Better but not perfect.