I want to make some clean-up with auto-generated files. How can I delete all the files matching some regexp mask from within elisp? As an example of desired functionality... Something like the line below:
(delete-file "*.txt") should delete all the text files in the current working directory...
(dolist (filename (directory-files "working-dir")) (when (string-match-p "\\.txt\\'" filename) (delete-file (file-name-concat "working-dir" filename)))) 
dired? dired. Maybe you can write an answer that uses dired, if you're familiar with it. match argument in directory-files and avoid the explicit string-match. Using dired as @FranBurstall suggested in a comment: use C-x C-f (find-file) on the directory, mark files for deletion with % d (dired-flag-files) followed by some regexp (e.g. .*\.txt$ - note that this is a regexp, not a glob and it specifies files whose names end with .txt), then after looking to make sure that you've got all the files you want and only those, press x to execute the deletions. Otherwise, press U to unmark everything and try again.
Here is a slightly improved version of shynur's snippet, that covers my needs. I've included NickD's comment and also replaced file-name-concat with concat since the former is not present in my Emacs version (27.1):
(defun my/delete-regexped-files (mask) ;; Delete all the files in the current directory that ;; match given regular expression. ;; Examples of mask: "\\.org~\\'", "\\.txt\\'" (dolist (filename (directory-files "" nil mask) ) (delete-file filename )))