Pipes wasn't a thing until v7.something or other. A bunch of lexical functions weren't implemented until then too.
> In OpenVMS Version 7.1, the DCL PIPE command was introduced.
Ask me how I really know OpenVMS v6 doesn't have pipes.
[1] http://h30266.www3.hpe.com/odl/axpos/opsys/vmsos84/6489/6489...