#!/user/local/bin/perl
use warnings;
use strict;

sub IN($){
  print shift;
  my $ret = <STDIN>;
  chomp $ret;
  return $ret;
}

my $a;
my $b;

$a = shift || IN("Enter value for b:");
if($b = shift){} else{ print "Enter value for c:"; chomp ($b = <STDIN>); }

print "a: $a\n";
print "b: $b\n";