macOS has a neat program for opening files, directories, and urls from the command line.

open file.ext

will open file.ext from your current directory in whatever default app you have configured for the given files’ extension. For example open paper.pdf will open Preview or another PDF viewer and open foobar.py will open the editor you have configured for .py files (configurable in Finder).

It can also open directories for viewing in Finder with open /path/to/my/dir or even urls with open https:example.com in your default web browser.