shell: save and restore mtime based on sha1 hash

Question

I have a set of several thousand files that are automatically re-generated every 24-hours (e.g. ports-readmes on OpenBSD).

Most of the time, the content of these files doesn't change, but since they are re-created, the mtime does change.

Without modifying the original app which re-generates the files in place, how would I cache the mtime based on the filename/sha1 pairs, and restore after the regeneration if sha1 stays the same? Prefer python, but any UNIX solution is welcome.

(I require this for a sitemap, since the sitemap spec only has lastmod for versioning.)

This is an entirely general problem, and could most certainly be solved through a rather small script. — cnst, Mar 12 '13 at 06:23
@cnst - Agreed. So try to write that small script. If you have trouble, come back with a specific question. You'll get plenty of answers then. — Robᵩ, Mar 12 '13 at 06:26

score 1 · Accepted Answer · answered Mar 12 '13 at 06:46

It isn't clear precisely what help you require. Here are some places to start:

You can use os.walk, os.listdir or glob.glob to generate a list of files.
You can use os.stat to determine the last modified time.
You can use hashlib.md5(open(fname).read()).hexdigest() to get the md5.
You can use os.utime to set the modified time of a file.
You can use json.dump and json.load to persist the mtimes from one run to the next (there are other alternatives)

shell: save and restore mtime based on sha1 hash

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