You might want to look at Term::ReadLine.

But, if having to press enter is acceptable, here's one method without using that module:

print "Do you want to run live tests (y/n)? ";
my $answer = <STDIN>; # beware of trailing newlines
if ($answer =~ /^n/i) { $foo = 0 }
elsif ($answer =~ /^y/i { $foo = 1 }
else { $foo = $default_foo } # default
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Or, you could repeat question with a goto LABEL or by wrapping it in a loop and only breaking out when an answer is acceptable.