select returns the currently selected filehandle. So, this is doing what you appear to expect: 

select(ERRFP), $| = 1

[download]

then, within its parentheses, it generates a list: 

(last_selected_filename, 1)

[download]

Taking the first index of that list ((last_selected_filename, 1)[0]) gives: 

last_selected_filename

[download]

Finally, this leaves you with: 

select(last_selected_filename);

[download]

In short, you select ERRFP and make it unbuffered, then reselect the original filehandle. All in one line. Haven't seen this is ages. :-)

Update: I just remembered where I did see this last: using format about a decade ago. See perlform - Format Variables for examples of less uglier ways to do the same thing.

-- Ken

In reply to Re: Strange piece of code! by kcott
in thread Strange piece of code! by solegaonkar

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