#!perl -w
 use strict;

 my $var;
 traverse($_, \$var) for @ARGV;
 print $var;

 sub traverse {
    my($node, $var)= @_;
    $$var .= $node . "\n";
    traverse($node, $var) unless length $$var > 10;
        # to show it work recursively
} 
__END__

varref a b c d
a
a
a
a
a
a
b
c
d