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How can I filter directory contents to return the highest numeric named directory? For example, suppose (directory-files "/some/dir") returns:

("." ".." "4.03.0" "4.02.9" "archives" "config" "log")

How can I extract the string "4.03.0"?

I tried using seq-remove with a regexp based predicate, but could not get it to work. Suggestions and insights appreciated. Thanks.

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1 Answer 1

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directory-files accepts match-regexp argument:

(directory-files "my/path/to/dir" nil "^[0-9][0-9.]*$")

should return ("4.03.0" "4.02.9") and you extract the first element of the list using functions first or car.

If you really want to use seq-remove, you can do that too:

(seq-remove
 (lambda (s)
   (not (string-match "^[0-9][0-9.]*$" s)))
 '("." ".." "4.03.0" "4.02.9" "archives" "config" "log"))
==> ("4.03.0" "4.02.9")

Note that ^[0-9.]$ matches "." and "..".

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  • Thanks for the helpful answer. Does directory-files ensure descending ordering? If not, is there a way to extract the target string independent of directory list order (i.e. assuming no particular order)?
    – Ari
    May 19, 2017 at 17:18
  • @Ari: You are welcome. Order is determined by the 4th argument to directory-files. If that is not your question, you should close this one and ask another one.
    – sds
    May 19, 2017 at 17:20
  • 2
    @Ari: emacs is self-documenting, so you can find out about a function by asking emacs about it: C-h f directory-files e.g. will tell you what the function does and what arguments it takes. There is a similar facility for variables. Just do C-h ? to get more information.
    – NickD
    May 19, 2017 at 18:21

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