Remove duplicates for "open with" in OS X From https://github.com/atom/atom/issues/1720
This does happen with other applications, and there's uncertainty about whether it's an OS X or Atom bug, consensus seems to be OS X. I worked around it by adding the recommended commands to an alias to my .bash_profile so I can just do killdups when it happens:
alias killdups='/System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user;killall Finder;echo "Rebuilt Open With, relaunching Finder"'
Reload .bash_profile with:
Then run in Terminal: