foreach $a ( 0,1,2 ) {
  unless ( $a ) {
    print "a is 0 or undef\n";
  }
  elsif ( $a == 1 ) {
    print "a is 1\n";
  }
  else {
    print "a equals $a\n";
  }
}

__END__
a is 0 or undef
a is 1
a equals 2