Hello james28909,

the possibility entirely depends on the executable: it accepts input? some program accept input on their STDIN, others ignore it. For example firefox does not accepts inputs:

 perl -e "print 'www.perlmonks.org'"| "C:\Program Files (x86)\Mozilla 
+Firefox\firefox.exe"
[download]

produce nothing but de default firefox page opened in a new instance of the program.
grep (i use the win32 port) by other hand, it accepts things in input:

perl -e "print 'www.perlmonks.org'"| grep w
www.perlmonks.org

perl -e "print 'www.perlmonks.org'"| grep XXXX
[download]

Some program accept some filename as data file, so you can let your Perl's program write such datafile:

 perl -e "open $fh,'>','perlcreated.txt' or die" && notepad perlcreate
+d.txt
[download]

When notepad is called the file yet exists.
Or the executable can accept data on a specific port, listening on a socket opened on that port, like a webserver...

There are a lot of possibilities but they all depends on the executable behaviour: it has some ear? or is deaf and dull?

L*

UPDATE: note the the term 'parent program' is a little misleading: parent and child parallel is used when a program spwan some other process, possibly with the intention to comunicate eachothers: the program is one but procesess can be many.

L*