unless ( -l "foo" ) { # we get here fine
    #*now* the link is created
    open( FH, ">>foo" ) or die "foo: $!";
    #and now it's removed again
}
die "Link attack detected" if ( -l "foo" or ! -e _ );

# we have checked for both existence and "type == symlink" on the same stat call,
# so either it's a link, or it's non-existent, or it's safe to write output