How to send a var to stdin of an external software

[Benjamin Watine]

Hi the list,

I need to send a var to stdin of an external soft ("cat" command for 
example).

How can I do this ? I would like a function like that :

	theFunction ('cat -', stdin=myVar)

I don't need to get any return value.

Another related question : Is there's a limitation of var size ? I would 
have var up to 10 MB.

Thanks !

Ben