Update: I got that wrong. See the correct explanation from ikegami (below).

While the problem has been solved, it has not been explained. In the first line: 

@piped = <STDIN>;

[download]
Reading <STDIN> in list context reads until the end of file for STDIN. At that point, you can no longer read from STDIN, so line 4 fails: 
$user_input = <STDIN>;

[download]
The solutions suggested either avoid using STDIN for user input (reading from the console) or close and re-open STDIN.

In reply to Re: STDIN problemo by eye
in thread STDIN problemo by ccdoub

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