Of the 300 new features in Leopard (Mac OS 10.5), Time Machine may be the one that excites me the most. I've already used to to repair applications after failed updates, pull back browser history items from two months ago, and restore emails that I had inadvertently flushed.

Yesterday, I found a new use for Time Machine: reviving IRb command history.

Over at eduFire, we've been working on converting user profile pictures from file system store to S3 backed storage. Since we're using the attachment_fu plugin, it seemed that the easiest way would be to just create a new instance of the user profile picture and feed in the path to the file.

While using attachment_fu in a controller is beautifully simple, requiring just an uploaded_data parameter, manipulating files through script/console is a bit more difficult. I knew we had wrestled with this back in February, when we changed the default thumbnail resolutions, and had to reprocess everyone's photos. What I had failed to do back then was document how we actually achieved it.

I have my IRb history logging to ~/.irb_history, but with only 500 lines of scrollback, I knew that there was no chance an entry from three months ago had survived. My first attempt to view the file in Time Machine was unsuccessful, as I couldn't seem to figure out how to get Time Machine to display dot-files.

However, the Time Machine archive is browsable in Terminal; after finding the path to the relevant backup (which looked something like this: /Volumes/Time Machine Drive/Backups.backupdb/AlloyCode/2008-03-03-000650/Macintosh HD/Users/jared), I was able to open the .irb_history file in TextMate and find the command I had lost.

For those who might need to do a similar operation in the future, here's how to recreate a file attachment in script/console:

Avatar.create(:filename => filename, :content_type => content_type, :temp_path => temp_path)

In the above example, filename corresponds to the name to save the attachment as on the server, content_type is the MIME type, and temp_path is the full path to the actual asset.