dired-flag-files-regexp).
The #, ~ and . commands flag many files for deletion, based on their file names. These commands are useful precisely because they do not actually delete any files; you can remove the deletion flags from any flagged files that you really wish to keep.
# flags for deletion all files whose names look like auto-save files (see section Auto-Saving: Protection Against Disasters)---that is, files whose names begin and end with `#'. ~ flags for deletion all files whose names say they are backup files (see section Backup Files)---that is, whose names end in `~'.
. (Period) flags just some of the backup files for deletion: all
but the oldest few and newest few backups of any one file. Normally
dired-kept-versions (not kept-new-versions; that
applies only when saving) specifies the number of newest versions of
each file to keep, and kept-old-versions specifies the number of
oldest versions to keep.
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.
The % d command flags all files whose names match a specified
regular expression (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 subdirectories
by hiding them (see section Hiding Subdirectories).