(debian-policy.info)Version

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5.6.12 ‘Version’
----------------

The version number of a package.  The format is:
‘[epoch:]upstream_version[-debian_revision]’.

The three components here 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.

     Epochs can help when the upstream version numbering scheme changes,
     but they must be used with care.  You should not change the epoch,
     even in experimental, without getting consensus on debian-devel
     first.

‘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 (1) and the
     characters ‘.’  ‘+’ ‘-’ ‘~’ (full stop, plus, hyphen, tilde) and
     should start with a digit.  If there is no ‘debian_revision’ then
     hyphens 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 a Debian package,
     where the Debian package source must always be identical to the
     pristine source and therefore no revision indication is required.

     It is conventional to restart the ‘debian_revision’ at ‘1’ each
     time the ‘upstream_version’ is increased.

     The package management system 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’ is equivalent to a ‘debian_revision’ of ‘0’.

When comparing two version numbers, first the epoch of each are
compared, then the ‘upstream_version’ if epoch is equal, and then
‘debian_revision’ if ‘upstream_version’ is also equal.  epoch is
compared numerically.  The ‘upstream_version’ and ‘debian_revision’
parts are compared by the package management system using the following
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 from earliest to latest: ‘~~’,
‘~~a’, ‘~’, the empty part, ‘a’.  (2)

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.

Epochs should be used sparingly

   ---------- Footnotes ----------

   (1) Alphanumerics are ‘A-Za-z0-9’ only.

   (2) One common use of ‘~’ is for upstream pre-releases.  For example,
‘1.0~beta1~svn1245’ sorts earlier than ‘1.0~beta1’, which sorts earlier
than ‘1.0’.