Changing default applications on a Mac using the command line & then a shell script

I use Markdown a lot, so I’m constantly creating files that end in the .md extension. For a while I wanted the very nice (& free for now!) app Mou to open those, but now I’ve switched to Sublime Text for my Markdown editing¹. So when I click on foo.md, I want it to open in Sublime Text instead of Mou.

Most Mac users of even mid-level sophistication know the drill: right-click on any file ending in .md, choose Get Info (or just select the file & press Command-I), find the Open With section, select Sublime Text, press Change All, press Continue when asked if I’m sure, close the Info window, done. It’s been that way for years, & it works fine.

But I want to use the command line instead.

Why use the command line when the process is pretty easy to do with a GUI?

• I can keep all my changes listed in one file, so I have a record of what I changed.
• I can make all my changes at one time (like after I’ve done a clean reinstall), in a few seconds.
• Periodically, I find that when I right-click on a file, the programs list shows duplicates, sometimes a lot of duplicates. After I fix that problem (using the command line, natch), I’d like to quickly re-set my default apps.
• I like the command line.

So here’s how to do it. Before you can jump in, though, you need to install a program & also know how to gather a few pieces of key information. Let’s walk through those things first.

duti

The program that makes it easy to change default apps via the command line is a free, open source app named duti². You can grab the source code at Sourceforge³. Download it, untar it, cd into the directory, & then do the classic three steps⁴:

./configure
make
sudo make install

This results in the duti executable going in /usr/local/bin/ & its man page getting placed into /usr/local/share/man/man1/. Easy enough.

Find out the current default for an extension

Why do this? Just so I can verify the current default, & then verify that any changes I make took.

So what’s currently the default for .md? Let’s find out:

$ duti -x md
Mou.app
/Applications/Mou.app
com.mouapp.Mou

The three line result tells me:

1. The name of the app
2. The app’s location on your Mac
3. The app’s bundle ID, a unique identifier for each program that normally is written in a reverse-domain-name style (like com.apple.mail or com.barebones.bbedit)

Find out the bundle ID for an app

I want to change from Mou to Sublime Text, so I need Sublime Text’s bundle ID. There are a couple of ways I could get this info.

If I knew that another file type foo already uses Sublime Text as its default, I could use duti -x foo & look at the third line of the results, as with Mou above.

OR I can use this one-line AppleScript:

$ osascript -e "id of app "Sublime Text 2"" 
com.sublimetext.2

This works for any app on your system, like this:

$ osascript -e "id of app "Espresso""
com.macrabbit.Espresso

Or this:

$ osascript -e "id of app "Mailplane 3""
com.mailplaneapp.Mailplane3

Change the default app

I know the extension I want to change (.md) & the bundle ID of the app that I want to open that extension (com.sublimetext.2), so let’s use duti to do it:

duti -s com.sublimetext.2 .md all

The -s means “set”. In order, I tell duti the bundle ID of the app, the extension of the files, & all means “all files with that extension”.

Now I verify my change:

$ duti -x md
Sublime Text 2.app
/Applications/Sublime Text 2.app
com.sublimetext.2

Create a shell script

Now let’s put everything together into a shell script that you can run anytime you need to. Copy & paste the script below into a file, save it as set_default_apps.sh, make sure it’s executable (chmod 755 set_default_apps.sh), & then run it when you feel like it.

Of course, you will want to change this script, specifically the here document you see that starts with { cat <<eof & ends with eof. For each line, put the bundle ID for the app you want to use, then a colon, and then the extension that you want to change so that it uses the bundle ID (com.sublimetext.2:md is a good example). I sorted my list by extension, but really, it doesn’t matter.

#!/bin/bash

#========================================================================
#  FILE:  set_default_apps.sh
#  DESCRIPTION:  Changes default apps for extensions
#  AUTHOR:  Scott Granneman (RSG), scott@chainsawonatireswing.com
#  COMPANY:  Chainsaw on a Tire Swing (http://ChainsawOnATireSwing.com)
#  VERSION:  0.1
#  CREATED:  09/17/2012 21:44:01 CDT
#  REVISION:   
#========================================================================

{ cat <<eof
com.macrabbit.Espresso:css
com.valloric.Sigil.app:epub
cx.c3.theunarchiver:gz
com.sublimetext.2:markdown
com.sublimetext.2:md
com.sublimetext.2:mdwn
com.sublimetext.2:mediawiki
cx.c3.theunarchiver:rar
com.sublimetext.2:sh
cx.c3.theunarchiver:tar
com.sublimetext.2:text
com.sublimetext.2:txt
com.sublimetext.2:xml
cx.c3.theunarchiver:zip
eof
} | grep . |
while IFS=$':' read bundle_id extension ; do
  # Grep to see if Bundle ID exists, sending stdout to /dev/null
  /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -dump | grep $bundle_id > /dev/null  
  # Save exit status (0=success & 1=failure)
  status=$?
  # If exit status failed, notify me & exit; if not, change default app for extension
  if test $status -eq 1 ; then
    echo "$bundle_id doesn't exist! Fix the script!"
    exit
  else
    echo -e "\nChanging $extension so it opens with $bundle_id …\n"
    duti -s $bundle_id .$extension all
    echo -e "Here's proof…\n"
    duti -x $extension
    echo -e "\n----------"
  fi
done

I hope this helps you as much as it helps me.