The downside is that I cant seem to get STDOUT before the program has ran for quite a while, then it spewes out some chuncks of STDOUT.

If the executable is using buffered IO on stdout (the norm), then the pipe won't get any data until the program has filled that buffer.

In addition, the pipe itself has a 4k buffer, which can further defer the flow of data into your perl script.

There is little you can do about this unless you have the source to the executable and can turn autoflushing on STDOUT.

Windows problem propably.

Nope. You'd be in exactly the same situation under *nix.

But my backup solution is to use the .exe files EXPORT function (built in reporting function, not related to perl). However, I would need to "PRESS" the the button "ESC" to the program, for it to quit and write the log files. Is this even possible?

Do you need to capture the exes stdout when you are using the "EXPORT function"? Ie. You said: "for it to quit and write the log files." which suggests that in this mode the data you want is written to a file rather than stdout.

If you do not need to capture stdout, then you may be able to feed the escape to the program via stdin:

open SYS,"| windows_exe_file.exe" or die ...;
print SYS "EXPORT this and that to thisFile.dat";
print SYS "\e";
close SYS;

my @data = do{ open IN, 'thisFile,dat'; local $/; <IN> };
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Otherwise, you'll probably need to use IPC::Open2 or a similar module.