`open` command to open a file in an application

Why can't I run this command in my terminal: open index.html Wasn't it supposed open this file on my browser? Also can't I run this command: open index.html -a "Sublime Text". The result of these commands are: $ open index.html Couldn't get a file descriptor referring to the console $ open index.html -a "Sublime Text" - open: invalid option -- 'a' Usage: open [OPTIONS] -- command