Most Unix systems have a little program called "yes"¹, which simply repeatedly outputs a string (by default "y\n") in order to answer questions like the one you mentioned. With that, the task essentially becomes a piped open:

#!/usr/bin/perl -l
# foo.pl

print "Hello world. Should I continue? (y/n)";
my $answer = <STDIN>;

print "Ok, you said $answer";
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#!/usr/bin/perl

open my $foo, "yes | ./foo.pl |" or die $!;

while (<$foo>) {
    print ": $_";
}
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$ ./876596.pl
: Hello world. Should I continue? (y/n)
: Ok, you said y
:
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¹ if you don't have it, you can trivially write it yourself...

Update:

Of course, if you want to actually read the questions (and only respond with 'y' to "Hello world. Should I continue?", instead of every question), you'd have to set up bidirectional communication, e.g. using IPC::Open3.