C:\Users\ken\tmp>perl -E  "my $input = 'none'; $input = <STDIN> if defined fileno(STDIN); say $input"
qwerty
qwerty


C:\Users\ken\tmp>perl -E  "my $input = 'none'; close STDIN; $input = <STDIN> if defined fileno(STDIN); say $input"
none

C:\Users\ken\tmp>