Yay! I used the open (PIPE,"blah") method and it worked!

Seeing what you chose to omit in your shortened rendition of the method, I hope you realize that what matters here is not the name "PIPE" for the handle, but the | at the end of the second argument to open. I.e. it would have worked just as well if you had used

open( THIS_IS_NOT_A_PIPE,"printsth $arg |" ) or die $!;

while ( <THIS_IS_NOT_A_PIPE> ) {
  print;
}
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