Here is an example of using files on disk to communicate between an external process and 4D:

1) Create a batch file named myBatch.bat next to a structure file and put the following into it:

echo 1 > in_progress ping 127.0.0.1 -n 10 del in_progress

The batch file will create a file named in_progress with the contents of 1.
Then ping the loopback address (127.0.0.1) 10 times.
Finally the batch file will delete the file named in_progress as it completes.

2) Create a method in the 4D Structure file with the following contents:

C_LONGINT($a;$winRef;$SH;$SW;$WH;$WW) C_TEXT($in;$out;$err;$folder;$inProgress_t) $folder:=Get 4D folder(Database Folder) $inProgress_t:=$folder+"in_progress" $SW:=Screen width\2 $SH:=(Screen height\2) $WW:=200\2 $WH:=50\2 $a:=0 $winRef:=Open window($SW-$WW;$SH-$WH;$SW+$WW;$SH+$WH;Plain fixed size window;"LEP") SET ENVIRONMENT VARIABLE("_4D_OPTION_CURRENT_DIRECTORY";$folder) SET ENVIRONMENT VARIABLE("_4D_OPTION_HIDE_CONSOLE";"true") SET ENVIRONMENT VARIABLE("_4D_OPTION_BLOCKING_EXTERNAL_PROCESS";"false") LAUNCH EXTERNAL PROCESS("cmd.exe /C myBatch.bat > out.txt 2> err.txt") DELAY PROCESS(Current process;1) While (Test path name($inProgress_t)=Is a document)    GOTO XY(0;0)    If (Mod($a;2)=0)       MESSAGE("operation in progress ")    Else       MESSAGE("operation in progress_")    End if    $a:=$a+1    DELAY PROCESS(Current process;10) End while CLOSE WINDOW($winRef) ALERT("done")

3) Run the 4D method.

When you run the 4D method a batch file will be executed. The console window is being hidden and the standard output of the batch file is being redirected to a file named out.txt while the standard error is redirected to err.txt. As the batch file starts it will create a file named in_progress with the contents of 1 and it will delete the file named in_progress as the batch file completes. While the file on disk exists the 4D code is waiting in a while loop and displaying a message to indicate an operation is in progress. Once the in_progress file is removed from disk the 4D code continues running and the message window is removed.

* This example can be improved by examining / processing the out.txt and err.txt files

---

In addition to demonstrating file-based communication, this example also demonstrates console redirection (a feature of cmd.exe) to redirect the stdOut and stdErr to files. You can test that using this from a command prompt:

myBatch.bat > out.txt 2> err.txt

the out.txt file would contain the std out.
the err.txt file would contain the std error messages.

Console Redirection is a feature of Windows and is documented here:
https://support.microsoft.com/en-us/kb/110930

We also discuss console redirection here:
http://kb.4d.com/assetid=75938