Is there a way to check if input is present on standard input (*STDIN) ...

• in a non-blocking way
• without waiting for user interaction
• in any version of perl 5 with bulit-in functionality (other than via &Term::ReadKey::ReadKey)

... when input is provided as program.pl < file?

I had tried (before finding T'R) ...

• both of $in = <STDIN> and getc( STDIN ) wait for user input;
• -[tpS] file tests don't provide the information.

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