The #, ~, ., % &, and % d commands flag many files for deletion, based on their file names:
dired-flag-auto-save-files) flags all files whose
names look like auto-save files—that is, files whose names begin and
end with ‘#’. See Auto Save.
dired-flag-backup-files) flags all files whose names
say they are backup files—that is, files whose names end in
‘~’. See Backup.
dired-clean-directory) flags just some of
the backup files for deletion: all but the oldest few and newest few
backups of any one file. Normally, the number of newest versions kept
for each file is given by the variable
kept-new-versions; that applies only when saving).
The number of oldest versions to keep is given by the variable
Period with a positive numeric argument, as in C-u 3 .,
specifies the number of newest versions to keep, overriding
dired-kept-versions. A negative numeric argument overrides
kept-old-versions, using minus the value of the argument to
specify the number of oldest versions of each file to keep.
% & (
dired-flag-garbage-files) flags files whose names
match the regular expression specified by the variable
dired-garbage-files-regexp. By default, this matches certain
files produced by TeX, ‘.bak’ files, and the ‘.orig’ and
‘.rej’ files produced by
% d flags all files whose names match a specified regular
dired-flag-files-regexp). Only the non-directory
part of the file name is used in matching. You can use ‘^’ and
‘$’ to anchor matches. You can exclude certain subdirectories
from marking by hiding them while you use % d. See Hiding Subdirectories.