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Finder's 'Open With' Touches Modification Times?

Something doesn't add up here.

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From Mac OS X Hints today. Submitted by 'auntchilada'.

This hint is about touching files from the Finder to update their mod time, much as you can do in Terminal with the touch command. Here's how:

  1. Select files to be 'touched' in the Finder.
  2. Press Command-Option-I to open the multiple item info inspector window (File » Show Inspector).
  3. Toggle/activate the Open With pop-up menu. You needn't select anything, just click to activate the menu.

The file's modified timestamp will be updated to now time; tested in 10.6.2.

The hint has so far garnered two votes for an average of 1/5. The only commenter 'jfa643' couldn't get it to work. Rob Griffiths says he could get it to work but not in the way advertised.

In my testing, I didn't have any luck with the time changing just by merely activating the menu; I had to select the currently-active option for the chosen files. If I selected files with different Open With settings (such that the pop-up menu reads Not Applicable) I couldn't change the modification timestamp at all via this method.

But no matter how mtime is touched it's still worrying: Apple's OS X is supposed to be Unix-compliant and their HFS+ is supposed to emulate and support Unix file system intrinsics.

FreeBSD Unix supports four time stamps; Apple's HFS+ five. The time stamps correspond as follows.

Unix (FreeBSD)Apple's HFS+
atime (accessed)access
b(irth)time (created)create
ctime (changed)attributeMod
mtime (modified)contentMod

For many practical reasons, the 'modified' time stamp (either mtime or contentMod) is supposed to only reflect a change in the file's (or the directory's) contents. Special 'Finder hints' about how to open a file - platform dependent extended attributes - do not access the file's contents and should therefore not affect the file's modified time. Some of this data isn't attached to the file anyway - it goes into the launch services database.

Of course a lot depends on exactly what that confused 'file manager' of Apple's means by 'modified' but it doesn't bode for good in any case - modifying extended attributes namely only bumps the ctime/attributeMod field; 'modified' is not affected.

See Also
Mac OS X Hints: Set files' modification time from Finder

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