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
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).