sub foo { my $x= $_[0] if ! defined $x; print "(@_):", ++$x, " "; undef $x if @_ && shift; } foo($_) for( 0,0,5,4,3,0,5,0,4,0,3 ); print $/, $x= 10, $/; foo($_) for( 0,0,5,4,3,0,5,0,4,0,3 ); print $/;