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After doing a Wordpress upgrade I notice that there are some files that have an old creation date. Am I safe to delete these on the assumption that they were part of the previous release and so aren't needed for the latest release?

I've used windiff to compare two different downloaded releases (i.e. not my live site) and I can spot files that were in the old, but not in the new, but it would be easier to get rid of the old ones if the answer to my question above was "yes".

For example, comparing 3.2.1 with 3.3.1 there are 80 files in 3.2.1 not present in 3.3.1. Here are a few:

  • wp-admin\css\login-rtl.css
  • wp-admin\css\login.css
  • wp-admin\css\ms.css
  • wp-admin\css\nav-menu-rtl.css
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Can you list some filenames of such files? – artlung Mar 16 '12 at 18:07
They could be part of the previous release but still used by the new release. I wouldn't delete WP core files ever. – Jared Mar 16 '12 at 18:15
@artlung I've done that. – paulmorriss Mar 19 '12 at 9:58
up vote 2 down vote accepted

For several versions already core updates are partial (differential). Only changed files are downloaded and overwritten so it is not safe to assume that those that weren't are not used.

However, you can compare downloads of two full releases to see which file aren't used any more.

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If you go and download archive from the site what you get is full package for that version. It's not what update process does in recent versions - it downloads different archive of files changed since version installed. – Rarst Mar 19 '12 at 10:38

There are differences in the root files from a new download of 3.3.1 and an release archive of 2.9.2 (there are probably differences in wp-admin and wp-includes, too, but I haven't checked):

2.9.2 root files 3.3.1 root files

The additional files in 2.9.2 have comments to the affect that they are deprecated and redirect to other files. On upgrades from 2.9.2 to 3.3.1, I have deleted the "extra files" in root that are not included in 3.3.1 with no ill effects.

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