NAME

       deb-version - Debian package version number format

SYNOPSIS

       [epoch:]upstream-version[-debian-revision]

DESCRIPTION

       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.

       upstream-version
              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 scheme.

              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.

       debian-revision
              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
              is.

              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
              “debianization” of it and therefore no revision indication is required.

              It  is  conventional  to restart the debian-revision at ‘1’ each 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-revision is the least significant part of the version number).

   Sorting algorithm
       The  upstream-version  and  debian-revision  parts  are compared by the package management
       system using the same algorithm:

       The strings are compared from left to right.

       First the initial part of each string  consisting  entirely  of  non-digit  characters  is
       determined.   These  two  parts  (one of which may be empty) are compared lexically.  If a
       difference is found it is returned.  The lexical  comparison  is  a  comparison  of  ASCII
       values  modified so that all the letters sort earlier than all the non-letters and so that
       a tilde sorts before anything, even the end of a part.  For example, the  following  parts
       are in sorted order: ‘~~’, ‘~~a’, ‘~’, the empty part, ‘a’.

       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 numbers containing strings of letters which the  package
       management system cannot interpret (such as ‘ALPHA’ or ‘pre-’), or with silly orderings.

NOTES

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

SEE ALSO

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