If you're really asking how to detect if STDIN is a terminal (when @ARGV is empty), I think the following works:

my @node_numbers;

if (@ARGV) {
   @node_numbers = @ARGV;
} else {
   die(<<"EOF") if -t STDIN;
#####################################
#
#  use args or < a text file
# 
#####################################
EOF

   { local $/; @node_numbers = split(' ', <STDIN>); }
}

# Do rest of code after here using @node_numbers
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