I think you mean a way to open Obsidian from the command line, but if you’re looking for a tool to just access notes, I use a program called Terminal Velocity 3 (https://github.com/aramiscd/tv3) . It has a filename search that lets you just start typing, and it filters matching results.
By default, it uses .txt formatting, but if you configure a .tvrc file in your home directory, you can set it up to use .md and the same root folder as Obsidian (I use a Dropbox synced folder):
[DEFAULT] # The filename extension to use for new files. extension = .md # The filename extensions to recognize in the notes dir. extensions = .txt, .md, .markdown, .rst notes_dir = ~/Dropbox/notes
This setup covers about 80% of what I would need from a command line tool, since I usually just can use the UI.