在emerge中clean prune与depclea unmerge 的区别是什么？

dgkgnrt

在emerge中clean prune与depclea  unmerge 的区别是什么？
解译一下

--unmerge (-C)
              WARNING: This action can remove important packages! Removes  all matching packages.  This does no checking of dependencies, so it may remove packages necessary for the proper operation  of  your system.  Its arguments can be ebuilds, sets, or atoms.

--prune (-P)
              WARNING: This action can remove important packages!  Prune looks  at each installed package and attempts to  remove  all  but  the
most  recently  installed  version.  Prune ignores slots, if you  require a slot-aware Prune use  emerge --clean.  Prune may inadvertently  remove  important  packages  from  your  system.  Use  --clean instead unless you really know what you're doing.

--depclean
              Determines all packages installed on the  system  that  have  no
  explicit  reason  for  being  there.  emerge generates a list of packages which it expects to be installed by checking the system  package  list and the world file.  It then compares that list to the list of packages which are actually installed;  the  differences are listed as unnecessary packages and then unmerged after  a short timeout.  WARNING:  Removing  some packages  may  cause  packages  which  link to the removed package to stop working and  complain about missing  libraries.   Re-emerge  the  complaining    package  to  fix this issue.  Also see --with-bdeps for behavior   with respect to build time dependencies that  are  not  strictly    required.

--clean (-c)
              Cleans  up  the  system  by examining the installed packages and      removing older packages.  This is  accomplished  by  looking  at each  installed package and separating the installed versions by  slot.  Clean will remove all but  the  most  recently  installed version  in  each slot.  Clean should not remove unslotted packages.  Note: Most recently  installed  means  most  recent,  not  highest version.