First thing that comes to mind is if @ARGV were empty (you're given no filenames) then check if -t STDIN is true (meaning it's a tty device not a pipe).

The cake is a lie.
The cake is a lie.
The cake is a lie.

In reply to Re: Using stdin only if there is input on it, but skipping it if there is no data by Fletch
in thread Using stdin only if there is input on it, but skipping it if there is no data by mldvx4

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