open

$ open directory_name

$ open file.txt

$ open image.png

$ open http://localhost:5000

From the macOS open manpage:

EXAMPLES
     "open '/Volumes/Macintosh HD/foo.txt'" opens the document in the default application for its type (as determined by LaunchServices).

     "open '/Volumes/Macintosh HD/Applications/'" opens that directory in the Finder.

     "open -a /Applications/TextEdit.app '/Volumes/Macintosh HD/foo.txt'" opens the document in the application specified (in this case, TextEdit).

     "open -b com.apple.TextEdit '/Volumes/Macintosh HD/foo.txt'" opens the document in the application specified (in this case, TextEdit).

     "open -e '/Volumes/Macintosh HD/foo.txt'" opens the document in TextEdit.

     "ls | open -f" writes the output of the 'ls' command to a file in /tmp and opens the file in the default text editor (as determined by LaunchServices).

     "open https://www.apple.com/" opens the URL in the default browser.

     "open 'file://localhost/Volumes/Macintosh HD/foo.txt'" opens the document in the default application for its type (as determined by LaunchServices).

     "open 'file://localhost/Volumes/Macintosh HD/Applications/'" opens that directory in the Finder.

     "open -h NSView" lists headers whose names contain NSView and allows you to choose which ones to open.

     "open -h NSView.h" immediately opens NSView.h.

     "open -h NSView -s OSX10.12" lists headers whose names contain NSView in the MacOSX 10.12 SDK and allows you to choose which ones to open.