Mac OSX change file association per file on the command line
This information is stored in the file's resource fork (Wikipedia). These resource forks are exposed as extended attributes (Wikipedia):
$ ls -l@ somefile.txt
-rw-r--r-- 1 danielbeck staff 0 18 Mär 19:00 somefile.txt
# setting non-default application using Finder
$ ls -l@ somefile.txt
-rw-r--r--@ 1 danielbeck staff 0 18 Mär 19:01 somefile.txt
com.apple.ResourceFork 1338
Editing from scratch is probably quite painful -- lots of binary data:
$ xattr -p com.apple.ResourceFork somefile.txt
00 00 01 00 00 00 05 08 00 00 04 08 00 00 00 32
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 04 04 00 00 00 32 2F 55 73 65 72 73 2F 64
61 6E 69 65 6C 62 65 63 6B 2F 41 70 70 6C 69 63
61 74 69 6F 6E 73 2F 53 75 62 6C 69 6D 65 20 54
65 78 74 20 32 2E 61 70 70 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 01 00 00 00 05 08
00 00 04 08 00 00 00 32 0C 00 00 00 C0 05 00 00
00 1C 00 32 00 00 75 73 72 6F 00 00 00 0A 00 00
FF FF 00 00 00 00 19 00 00 00
But you can treat these resource forks like files. For example:
$ open somefile.txt # opens in Sublime 2
$ cp somefile.txt/..namedfork/rsrc openInSublime2rsrc
$ open otherfile.txt # opens in TextEdit
$ cp openInSublime2rsrc otherfile.txt/..namedfork/rsrc
$ open otherfile.txt # opens in Sublime 2
/..namedfork/rsrc is how the resource fork is exposed to POSIX applications (i.e. probably everything you do in Terminal).
So you just need to create one "template" file from an existing resource fork (in this example openInSublime2rsrc), and you can copy it to your other files afterwards.
Picking up from Daniel Beck's answer above, this information is indeed stored in the file's resource fork. Apple provides two utilities, called "Rez" and "DeRez" with the developer tools, which allow you to manipulate resource forks. In particular, you can push a resource fork into a file with Rez.
To change the association of a single file from the command line, first create a file of the right type, and manually change its association to the application you want it to open in. This creates the resource fork in the file - if you don't do this, there'll be no information to copy out. Then, pull out the resource fork with DeRez, like this (assuming a file foo.txt, and that the application you want to use is Firefox.app).
DeRez foo.txt > foo.r
This will create a file called foo.r which is the decompiled resource fork as a text file. It will look something like this:
data 'usro' (0) {
$"0000 001A 2F41 7070 6C69 6361 7469 6F6E" /* ..../Application */
$"732F 4669 7265 666F 782E 6170 7000 0000" /* s/Firefox.app... */
$"0000 0000 0000 0000 0000 0000 0000 0000" /* ................ */
You can edit this if you want to create one from scratch, but you have to get the format exactly right or it won't work. It's just hex-encoded characters describing the path to the app bundle you want, terminated with a zero.
You might see a message saying that the resource fork is empty and uninitialised. If so, you haven't changed the per-file association on the source file, so you need to go do that, then re-run the DeRez command.
Once you have this, you can push this into another file as follows (assuming bar.txt exists):
Rez foo.r -a -o bar.txt
This updates bar.txt in place with the resource fork from foo.r.
To check it worked OK, since neither Rez nor DeRez print error messages, just do this:
DeRez bar.txt
You should see the same information as before. After all that, just open the file bar.txt as you normally would, and it should open in the correct application, not the default one.
To do a batch change, once you have the .r file, then you can use a standard wildcard expansion like this:
Rez foo.r -a -o *.txt
That'll do all the files that match the wildcard.
I have done this on 10.7, but it's my understanding that this works on earlier machines too.
I did it using xattr (it works perfectly on APFS volume)
xattr -wx com.apple.LaunchServices.OpenWith \
"`xattr -px com.apple.LaunchServices.OpenWith FILEWITHGOODTYPE`" FILETOCHANGE
It works by copying the OpenWith extended attribute from a file that is already associated with the right app, to a file that is not.