Doing any type of string search on a database file is not all that helpful since the binary file contains lots of links from table to table that "grep" cannot navigate.
The Lightroom catalog is a SQLite database. You can download the SQLite software and query the database if you so desire. There is not public documentation of for database structure; if you are not familiar with SQL databases, you may not find this all to helpful.
Thanks for the very helpful pointer. I've been able to view data in Lrcat backups using a sqlite viewer. I've found the point in time where the files are gone from the catalog in the AgLibraryFolder and AgLibraryFile tables.
This raises two more questions:
1) I don't see a change log of any sort. Does Lightroom keep a change history showing commands like the movement of File1 from Folder1 to Folder2, or deletion of File 1? For example, it might show "File1 moved from Folder1 to Folder 2."
2) Does anyone know of an existing script that can pull out file information for a list of files that I'll generally call metadata? In my case it might pull out file size, flag setting, color code, dimensions of photo, tags, etc. I could use deleted files in a CSV file as the input, the script would run, and the result for me would be a list that had Filename, Foldername, Metadata in a CSV. Or something like this.
1. Not as far as I know. Only Develop's History.
2. Your requirements sound very custom, so I'd say no. Look up my ListView plugin for one idea though.