examples/perl-io/Dockerfile
FROM ubuntu:16.10
COPY greetings.pl /opt/
CMD  perl /opt/greetings.pl
examples/perl-io/greetings.pl
use 5.010;
use strict;
use warnings;

print "What is your name? ";
my $name = <STDIN>;
chomp $name;
say "Hello $name, how are you today?";
$ docker run mydocker

Use of uninitialized value $name in scalar chomp at /opt/greetings.pl line 7.
Use of uninitialized value $name in concatenation (.) or string at /opt/greetings.pl line 8.
What is your name? Hello , how are you today?

We need to tell Docker that this is an interactive process

docker run -it mydocker