Thanks, Kingdomecome. It's true, calling xfe without '&' prevents further aterm input.
Unfortunately that's not my problem but just the aterm behaviour I want to create. And it's working fine.
After starting the below xfeAndConsole-script from aterm, aterm works as report console - if the line without '&' is used and the other outcommented.
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You can write Shell scripts with xfw, store and start them in xfe with double-click - and aterm reports your echo output immediately. Fine so far.
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But what's anoying are these Xlib-warnings. Within a beginners guide it doesn't help that they dissapear with a simple 'clear'.
For a beginner they create a barrier, as a beginner will get the impression of having done something wrong and better leave my tutorial.
So I need a way to get rid of these warnings.