Version  numbers  as used for Debian binary and source packages consist
       of three components. These are:

       epoch  This is a single (generally small) unsigned integer.  It may  be
              omitted,  in  which case zero is assumed.  If it is omitted then
              the upstream-version may not contain any colons.

              It is provided to allow mistakes in the version numbers of older
              versions  of  a  package,  and also a package's previous version
              numbering schemes, to be left behind.

              This is the main part of the version number.  It is usually  the
              version  number  of the original ("upstream") package from which
              the .deb file has been made, if  this  is  applicable.   Usually
              this  will  be  in  the  same  format  as  that specified by the
              upstream author(s); however, it may need to  be  reformatted  to
              fit  into  the package management system's format and comparison

              The comparison behavior of the package  management  system  with
              respect   to   the  upstream-version  is  described  below.  The
              upstream-version portion of the version number is mandatory.

              The upstream-version  may  contain  only  alphanumerics  ("A-Za-
              z0-9")  and  the  characters . + - : ~ (full stop, plus, hyphen,
              colon, tilde) and should start with a digit.   If  there  is  no
              debian-revision  then  hyphens  are  not allowed; if there is no
              epoch then colons are not allowed.

              This part of the version number specifies  the  version  of  the
              Debian  package  based  on the upstream version.  It may contain
              only alphanumerics and the characters + . ~  (plus,  full  stop,
              tilde)  and  is compared in the same way as the upstream-version

              It is optional; if it isn't present  then  the  upstream-version
              may not contain a hyphen.  This format represents the case where
              a piece of software was written specifically to be turned into a
              Debian  package,  and so there is only one "debianisation" of it
              and therefore no revision indication is required.

              It is conventional to restart the debian-revision  at  '1'  each
              time time the upstream-version is increased.

              Dpkg  will  break the version number apart at the last hyphen in
              the string (if there is one) to determine  the  upstream-version
              and  debian-revision.  The absence of a debian-revision compares
              earlier than the presence of one (but note that the debian-revi-
              sion is the least significant part of the version number).

       sorts  before  anything, even the end of a part.  For example, the fol-
       lowing parts are in sorted order: '~~', '~~a',  '~',  the  empty  part,

       Then  the  initial  part of the remainder of each string which consists
       entirely of digit characters is determined.  The  numerical  values  of
       these  two  parts are compared, and any difference found is returned as
       the result of the comparison.   For  these  purposes  an  empty  string
       (which  can  only occur at the end of one or both version strings being
       compared) counts as zero.

       These two steps (comparing and removing initial non-digit  strings  and
       initial digit strings) are repeated until a difference is found or both
       strings are exhausted.

       Note that the purpose of epochs is to allow us to leave behind mistakes
       in  version  numbering,  and  to cope with situations where the version
       numbering scheme changes.  It is not intended to cope with version num-
       bers  containing strings of letters which the package management system
       cannot interpret (such as 'ALPHA' or 'pre-'), or with silly orderings.

       The tilde character and its special sorting properties were  introduced
       in  dpkg 1.10 and some parts of the dpkg build scripts only gained sup-
       port for it later in the 1.10.x series.

       deb-control(5), deb(5), dpkg(1)

Debian Project                    2013-04-02                    deb-version(5)
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