path: root/doc/sort-version.texi

@c GNU Version-sort ordering documentation

@c Copyright (C) 2019--2022 Free Software Foundation, Inc.

@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, no Front-Cover Texts, and no Back-Cover
@c Texts.  A copy of the license is included in the ``GNU Free
@c Documentation License'' file as part of this distribution.

@c Written by Assaf Gordon

@node Version sort ordering
@chapter Version sort ordering



@node Version sort overview
@section Version sort overview

@dfn{Version sort} puts items such as file names and lines of
text in an order that feels natural to people, when the text
contains a mixture of letters and digits.

Lexicographic sorting usually does not produce the order that one expects
because comparisons are made on a character-by-character basis.

Compare the sorting of the following items:

@example
Lexicographic sort:          Version Sort:

a1                           a1
a120                         a2
a13                          a13
a2                           a120
@end example

Version sort functionality in GNU Coreutils is available in the @samp{ls -v},
@samp{ls --sort=version}, @samp{sort -V}, and
@samp{sort --version-sort} commands.



@node Using version sort in GNU Coreutils
@subsection Using version sort in GNU Coreutils

Two GNU Coreutils programs use version sort: @command{ls} and @command{sort}.

To list files in version sort order, use @command{ls}
with the @option{-v} or @option{--sort=version} option:

@example
default sort:              version sort:

$ ls -1                    $ ls -1 -v
a1                         a1
a100                       a1.4
a1.13                      a1.13
a1.4                       a1.40
a1.40                      a2
a2                         a100
@end example

To sort text files in version sort order, use @command{sort} with
the @option{-V} or @option{--version-sort} option:

@example
$ cat input
b3
b11
b1
b20


lexicographic order:       version sort order:

$ sort input               $ sort -V input
b1                         b1
b11                        b3
b20                        b11
b3                         b20
@end example

To sort a specific field in a file, use @option{-k/--key} with
@samp{V} type sorting, which is often combined with @samp{b} to
ignore leading blanks in the field:

@example
$ cat input2
100   b3   apples
2000  b11  oranges
3000  b1   potatoes
4000  b20  bananas
$ sort -k 2bV,2 input2
3000  b1   potatoes
100   b3   apples
2000  b11  oranges
4000  b20  bananas
@end example

@node Version sort and natural sort
@subsection Version sort and natural sort

In GNU Coreutils, the name @dfn{version sort} was chosen because it is based
on Debian GNU/Linux's algorithm of sorting packages' versions.

Its goal is to answer questions like
``Which package is newer, @file{firefox-60.7.2} or @file{firefox-60.12.3}?''

In Coreutils this algorithm was slightly modified to work on more
general input such as textual strings and file names
(see @ref{Differences from Debian version sort}).

In other contexts, such as other programs and other programming
languages, a similar sorting functionality is called
@uref{https://en.wikipedia.org/wiki/Natural_sort_order,natural sort}.


@node Variations in version sort order
@subsection Variations in version sort order

Currently there is no standard for version sort.

That is: there is no one correct way or universally agreed-upon way to
order items. Each program and each programming language can decide its
own ordering algorithm and call it ``version sort'', ``natural sort'',
or other names.

See @ref{Other version/natural sort implementations} for many examples of
differing sorting possibilities, each with its own rules and variations.

If you find a bug in the Coreutils implementation of version-sort, please
report it.  @xref{Reporting version sort bugs}.


@node Version sort implementation
@section Version sort implementation

GNU Coreutils version sort is based on the ``upstream version''
part of
@uref{https://www.debian.org/doc/debian-policy/ch-controlfields.html#version,
Debian's versioning scheme}.

This section describes the GNU Coreutils sort ordering rules.

The next section (@ref{Differences from Debian version
sort}) describes some differences between GNU Coreutils
and Debian version sort.


@node Version-sort ordering rules
@subsection Version-sort ordering rules

The version sort ordering rules are:

@enumerate
@item
The strings are compared from left to right.

@item
First the initial part of each string consisting entirely of non-digit
bytes is determined.

@enumerate A
@item
These two parts (either of which may be empty) are compared lexically.
If a difference is found it is returned.

@item
The lexical comparison is a lexicographic comparison of byte strings,
except that:

@enumerate a
@item
ASCII letters sort before other bytes.
@item
A tilde sorts before anything, even an empty string.
@end enumerate
@end enumerate

@item
Then the initial part of the remainder of each string that contains
all the leading digits is determined. The numerical values represented by
these two parts are compared, and any difference found is returned as
the result of the comparison.

@enumerate A
@item
For these purposes an empty string (which can only occur at the end of
one or both version strings being compared) counts as zero.

@item
Because the numerical value is used, non-identical strings can compare
equal.  For example, @samp{123} compares equal to @samp{00123}, and
the empty string compares equal to @samp{0}.
@end enumerate

@item
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.
@end enumerate

Consider the version-sort comparison of two file names:
@file{foo07.7z} and @file{foo7a.7z}. The two strings will be broken
down to the following parts, and the parts compared respectively from
each string:

@example
foo  @r{vs}  foo   @r{(rule 2, non-digits)}
07   @r{vs}  7     @r{(rule 3, digits)}
.    @r{vs}  a.    @r{(rule 2)}
7    @r{vs}  7     @r{(rule 3)}
z    @r{vs}  z     @r{(rule 2)}
@end example

Comparison flow based on above algorithm:

@enumerate
@item
The first parts (@samp{foo}) are identical.

@item
The second parts (@samp{07} and @samp{7}) are compared numerically,
and compare equal.

@item
The third parts (@samp{.} vs @samp{a.}) are compared
lexically by ASCII value (rule 2.B).

@item
The first byte of the first string (@samp{.}) is compared
to the first byte of the second string (@samp{a}).

@item
Rule 2.B.a says letters sorts before non-letters.
Hence, @samp{a} comes before @samp{.}.

@item
The returned result is that @file{foo7a.7z} comes before @file{foo07.7z}.
@end enumerate

Result when using sort:

@example
$ cat input3
foo07.7z
foo7a.7z
$ sort -V input3
foo7a.7z
foo07.7z
@end example

See @ref{Differences from Debian version sort} for
additional rules that extend the Debian algorithm in Coreutils.


@node Version sort is not the same as numeric sort
@subsection Version sort is not the same as numeric sort

Consider the following text file:

@example
$ cat input4
8.10
8.5
8.1
8.01
8.010
8.100
8.49

Numerical Sort:                   Version Sort:

$ sort -n input4                  $ sort -V input4
8.01                              8.01
8.010                             8.1
8.1                               8.5
8.10                              8.010
8.100                             8.10
8.49                              8.49
8.5                               8.100
@end example

Numeric sort (@samp{sort -n}) treats the entire string as a single numeric
value, and compares it to other values. For example, @samp{8.1}, @samp{8.10} and
@samp{8.100} are numerically equivalent, and are ordered together. Similarly,
@samp{8.49} is numerically less than @samp{8.5}, and appears before first.

Version sort (@samp{sort -V}) first breaks down the string into digit and
non-digit parts, and only then compares each part (see annotated
example in @ref{Version-sort ordering rules}).

Comparing the string @samp{8.1} to @samp{8.01}, first the
@samp{8}s are compared (and are identical), then the
dots (@samp{.}) are compared and are identical, and lastly the
remaining digits are compared numerically (@samp{1} and @samp{01}) -
which are numerically equal.  Hence, @samp{8.01} and @samp{8.1}
are grouped together.

Similarly, comparing @samp{8.5} to @samp{8.49} -- the @samp{8}
and @samp{.} parts are identical, then the numeric values @samp{5} and
@samp{49} are compared. The resulting @samp{5} appears before @samp{49}.

This sorting order (where @samp{8.5} comes before @samp{8.49}) is common when
assigning versions to computer programs (while perhaps not intuitive
or ``natural'' for people).

@node Version sort punctuation
@subsection Version sort punctuation

Punctuation is sorted by ASCII order (rule 2.B).

@example
$ touch 1.0.5_src.tar.gz 1.0_src.tar.gz
$ ls -v -1
1.0.5_src.tar.gz
1.0_src.tar.gz
@end example

Why is @file{1.0.5_src.tar.gz} listed before @file{1.0_src.tar.gz}?

Based on the version-sort ordering rules, the strings are broken down
into the following parts:

@example
          1   @r{vs}  1               @r{(rule 3, all digits)}
          .   @r{vs}  .               @r{(rule 2, all non-digits)}
          0   @r{vs}  0               @r{(rule 3)}
          .   @r{vs}  _src.tar.gz     @r{(rule 2)}
          5   @r{vs}  empty string    @r{(no more bytes in the file name)}
_src.tar.gz   @r{vs}  empty string
@end example

The fourth parts (@samp{.} and @samp{_src.tar.gz}) are compared
lexically by ASCII order. The @samp{.} (ASCII value 46) is
less than @samp{_} (ASCII value 95) -- and should be listed before it.

Hence, @file{1.0.5_src.tar.gz} is listed first.

If a different byte appears instead of the underscore (for
example, percent sign @samp{%} ASCII value 37, which is less
than dot's ASCII value of 46), that file will be listed first:

@example
$ touch   1.0.5_src.tar.gz     1.0%zzzzz.gz
1.0%zzzzz.gz
1.0.5_src.tar.gz
@end example

The same reasoning applies to the following example, as @samp{.} with
ASCII value 46 is less than @samp{/} with ASCII value 47:

@example
$ cat input5
3.0/
3.0.5
$ sort -V input5
3.0.5
3.0/
@end example


@node Punctuation vs letters
@subsection Punctuation vs letters

Rule 2.B.a says letters sort before non-letters
(after breaking down a string to digit and non-digit parts).

@example
$ cat input6
a%
az
$ sort -V input6
az
a%
@end example

The input strings consist entirely of non-digits, and based on the
above algorithm have only one part, all non-digits
(@samp{a%} vs @samp{az}).

Each part is then compared lexically,
byte-by-byte; @samp{a} compares identically in both
strings.

Rule 2.B.a says a letter like @samp{z} sorts before
a non-letter like @samp{%} -- hence @samp{az} appears first (despite
@samp{z} having ASCII value of 122, much larger than @samp{%}
with ASCII value 37).

@node The tilde @samp{~}
@subsection The tilde @samp{~}

Rule 2.B.b says the tilde @samp{~} (ASCII 126) sorts
before other bytes, and before an empty string.

@example
$ cat input7
1
1%
1.2
1~
~
$ sort -V input7
~
1~
1
1%
1.2
@end example

The sorting algorithm starts by breaking down the string into
non-digit (rule 2) and digit parts (rule 3).

In the above input file, only the last line in the input file starts
with a non-digit (@samp{~}). This is the first part. All other lines
in the input file start with a digit -- their first non-digit part is
empty.

Based on rule 2.B.b, tilde @samp{~} sorts before other bytes
and before the empty string -- hence it comes before all other strings,
and is listed first in the sorted output.

The remaining lines (@samp{1}, @samp{1%}, @samp{1.2}, @samp{1~})
follow similar logic: The digit part is extracted (1 for all strings)
and compares equal. The following extracted parts for the remaining
input lines are: empty part, @samp{%}, @samp{.}, @samp{~}.

Tilde sorts before all others, hence the line @samp{1~} appears next.

The remaining lines (@samp{1}, @samp{1%}, @samp{1.2}) are sorted based
on previously explained rules.

@node Version sort ignores locale
@subsection Version sort ignores locale

In version sort, Unicode characters are compared byte-by-byte according
to their binary representation, ignoring their Unicode value or the
current locale.

Most commonly, Unicode characters are encoded as UTF-8 bytes; for
example, GREEK SMALL LETTER ALPHA (U+03B1, @samp{α}) is encoded as the
UTF-8 sequence @samp{0xCE 0xB1}).  The encoding is compared
byte-by-byte, e.g., first @samp{0xCE} (decimal value 206) then
@samp{0xB1} (decimal value 177).

@example
$ touch aa az "a%" "aα"
$ ls -1 -v
aa
az
a%
aα
@end example

Ignoring the first letter (@samp{a}) which is identical in all
strings, the compared values are:

@samp{a} and @samp{z} are letters, and sort before
all other non-digits.

Then, percent sign @samp{%} (ASCII value 37) is compared to the
first byte of the UTF-8 sequence of @samp{α}, which is 0xCE or 206). The
value 37 is smaller, hence @samp{a%} is listed before @samp{aα}.

@node Differences from Debian version sort
@section Differences from Debian version sort

GNU Coreutils version sort differs slightly from the
official Debian algorithm, in order to accommodate more general usage
and file name listing.


@node Hyphen-minus and colon
@subsection Hyphen-minus @samp{-} and colon @samp{:}

In Debian's version string syntax the version consists of three parts:
@example
[epoch:]upstream_version[-debian_revision]
@end example
The @samp{epoch} and @samp{debian_revision} parts are optional.

Example of such version strings:

@example
60.7.2esr-1~deb9u1
52.9.0esr-1~deb9u1
1:2.3.4-1+b2
327-2
1:1.0.13-3
2:1.19.2-1+deb9u5
@end example

If the @samp{debian_revision part} is not present,
hyphens @samp{-} are not allowed.
If epoch is not present, colons @samp{:} are not allowed.

If these parts are present, hyphen and/or colons can appear only once
in valid Debian version strings.

In GNU Coreutils, such restrictions are not reasonable (a file name can
have many hyphens, a line of text can have many colons).

As a result, in GNU Coreutils hyphens and colons are treated exactly
like all other punctuation, i.e., they are sorted after
letters.  @xref{Version sort punctuation}.

In Debian, these characters are treated differently than in Coreutils:
a version string with hyphen will sort before similar strings without
hyphens.

Compare:

@example
$ touch 1ab-cd 1abb
$ ls -v -1
1abb
1ab-cd
$ if dpkg --compare-versions 1abb lt 1ab-cd
> then echo sorted
> else echo out of order
> fi
out of order
@end example

For further details, see @ref{Comparing two strings using Debian's
algorithm} and @uref{https://bugs.gnu.org/35939,GNU Bug 35939}.

@node Special priority in GNU Coreutils version sort
@subsection Special priority in GNU Coreutils version sort

In GNU Coreutils version sort, the following items have
special priority and sort before all other strings (listed in order):

@enumerate
@item The empty string

@item The string @samp{.} (a single dot, ASCII 46)

@item The string @samp{..} (two dots)

@item Strings starting with dot (@samp{.}) sort before
strings starting with any other byte.
@end enumerate

Example:

@example
$ printf '%s\n' a "" b "." c  ".."  ".d20" ".d3"  | sort -V
.
..
.d3
.d20
a
b
c
@end example

These priorities make perfect sense for @samp{ls -v}: The special
files dot @samp{.} and dot-dot @samp{..} will be listed
first, followed by any hidden files (files starting with a dot),
followed by non-hidden files.

For @samp{sort -V} these priorities might seem arbitrary. However,
because the sorting code is shared between the @command{ls} and @command{sort}
program, the ordering rules are the same.

@node Special handling of file extensions
@subsection Special handling of file extensions

GNU Coreutils version sort implements specialized handling
of strings that look like file names with extensions.
This enables slightly more natural ordering of file
names.

The following additional rules apply when comparing two strings where
both begin with non-@samp{.}.  They also apply when comparing two
strings where both begin with @samp{.} but neither is @samp{.} or @samp{..}.

@enumerate
@item
A suffix (i.e., a file extension) is defined as: a dot, followed by an
ASCII letter or tilde, followed by zero or more ASCII letters, digits,
or tildes; all repeated zero or more times, and ending at string end.
This is equivalent to matching the extended regular expression
@code{(\.[A-Za-z~][A-Za-z0-9~]*)*$} in the C locale.

@item
The suffixes are temporarily removed, and the strings are compared
without them, using version sort (see @ref{Version-sort ordering
rules}) without special priority (see @ref{Special priority in GNU
Coreutils version sort}).

@item
If the suffix-less strings do not compare equal, this comparison
result is used and the suffixes are effectively ignored.

@item
If the suffix-less strings compare equal, the suffixes are restored
and the entire strings are compared using version sort.
@end enumerate

Examples for rule 1:

@itemize
@item
@samp{hello-8.txt}: the suffix is @samp{.txt}

@item
@samp{hello-8.2.txt}: the suffix is @samp{.txt}
(@samp{.2} is not included because the dot is not followed by a letter)

@item
@samp{hello-8.0.12.tar.gz}: the suffix is @samp{.tar.gz} (@samp{.0.12}
is not included)

@item
@samp{hello-8.2}: no suffix (suffix is an empty string)

@item
@samp{hello.foobar65}: the suffix is @samp{.foobar65}

@item
@samp{gcc-c++-10.8.12-0.7rc2.fc9.tar.bz2}: the suffix is
@samp{.fc9.tar.bz2} (@samp{.7rc2} is not included as it begins with a digit)

@item
@samp{.autom4te.cfg}: the suffix is the entire string.
@end itemize

Examples for rule 2:

@itemize
@item
Comparing @samp{hello-8.txt} to @samp{hello-8.2.12.txt}, the
@samp{.txt} suffix is temporarily removed from both strings.

@item
Comparing @samp{foo-10.3.tar.gz} to @samp{foo-10.tar.xz}, the suffixes
@samp{.tar.gz} and @samp{.tar.xz} are temporarily removed from the
strings.
@end itemize

Example for rule 3:

@itemize
@item
Comparing @samp{hello.foobar65} to @samp{hello.foobar4}, the suffixes
(@samp{.foobar65} and @samp{.foobar4}) are temporarily removed. The
remaining strings are identical (@samp{hello}). The suffixes are then
restored, and the entire strings are compared (@samp{hello.foobar4} comes
first).
@end itemize

Examples for rule 4:

@itemize
@item
When comparing the strings @samp{hello-8.2.txt} and @samp{hello-8.10.txt}, the
suffixes (@samp{.txt}) are temporarily removed. The remaining strings
(@samp{hello-8.2} and @samp{hello-8.10}) are compared as previously described
(@samp{hello-8.2} comes first).
@slanted{(In this case the suffix removal algorithm
does not have a noticeable effect on the resulting order.)}
@end itemize

@b{How does the suffix-removal algorithm effect ordering results?}

Consider the comparison of hello-8.txt and hello-8.2.txt.

Without the suffix-removal algorithm, the strings will be broken down
to the following parts:

@example
hello-  @r{vs}  hello-  @r{(rule 2, all non-digits)}
8       @r{vs}  8       @r{(rule 3, all digits)}
.txt    @r{vs}  .       @r{(rule 2)}
empty   @r{vs}  2
empty   @r{vs}  .txt
@end example

The comparison of the third parts (@samp{.} vs
@samp{.txt}) will determine that the shorter string comes first -
resulting in @file{hello-8.2.txt} appearing first.

Indeed this is the order in which Debian's @command{dpkg} compares the strings.

A more natural result is that @file{hello-8.txt} should come before
@file{hello-8.2.txt}, and this is where the suffix-removal comes into play:

The suffixes (@samp{.txt}) are removed, and the remaining strings are
broken down into the following parts:

@example
hello-  @r{vs}  hello-  @r{(rule 2, all non-digits)}
8       @r{vs}  8       @r{(rule 3, all digits)}
empty   @r{vs}  .       @r{(rule 2)}
empty   @r{vs}  2
@end example

As empty strings sort before non-empty strings, the result is @samp{hello-8}
being first.

A real-world example would be listing files such as:
@file{gcc_10.fc9.tar.gz}
and @file{gcc_10.8.12.7rc2.fc9.tar.bz2}: Debian's algorithm would list
@file{gcc_10.8.12.7rc2.fc9.tar.bz2} first, while @samp{ls -v} will list
@file{gcc_10.fc9.tar.gz} first.

These priorities make sense for @samp{ls -v}:
Versioned files will be listed in a more natural order.

For @samp{sort -V} these priorities might seem arbitrary. However,
because the sorting code is shared between the @command{ls} and @command{sort}
program, the ordering rules are the same.


@node Comparing two strings using Debian's algorithm
@subsection Comparing two strings using Debian's algorithm

The Debian program @command{dpkg} (available on all Debian and Ubuntu
installations) can compare two strings using the @option{--compare-versions}
option.

To use it, create a helper shell function (simply copy & paste the
following snippet to your shell command-prompt):

@example
compver() @{
  if dpkg --compare-versions "$1" lt "$2"
  then printf '%s\n' "$1" "$2"
  else printf '%s\n' "$2" "$1"
  fi
@}
@end example

Then compare two strings by calling @command{compver}:

@example
$ compver 8.49 8.5
8.5
8.49
@end example

Note that @command{dpkg} will warn if the strings have invalid syntax:

@example
$ compver "foo07.7z" "foo7a.7z"
dpkg: warning: version 'foo07.7z' has bad syntax:
               version number does not start with digit
dpkg: warning: version 'foo7a.7z' has bad syntax:
               version number does not start with digit
foo7a.7z
foo07.7z
$ compver "3.0/" "3.0.5"
dpkg: warning: version '3.0/' has bad syntax:
               invalid character in version number
3.0.5
3.0/
@end example

To illustrate the different handling of hyphens between Debian and
Coreutils algorithms (see
@ref{Hyphen-minus and colon}):

@example
$ compver abb ab-cd 2>/dev/null     $ printf 'abb\nab-cd\n' | sort -V
ab-cd                               abb
abb                                 ab-cd
@end example

To illustrate the different handling of file extension: (see @ref{Special
handling of file extensions}):

@example
$ compver hello-8.txt hello-8.2.txt 2>/dev/null
hello-8.2.txt
hello-8.txt
$ printf '%s\n' hello-8.txt hello-8.2.txt | sort -V
hello-8.txt
hello-8.2.txt
@end example


@node Advanced version sort topics
@section Advanced Topics


@node Reporting version sort bugs
@subsection Reporting version sort bugs

If you suspect a bug in GNU Coreutils version sort (i.e., in the
output of @samp{ls -v} or @samp{sort -V}), please first check the following:

@enumerate
@item
Is the result consistent with Debian's own ordering (using @command{dpkg}, see
@ref{Comparing two strings using Debian's algorithm})? If it is, then this
is not a bug -- please do not report it.

@item
If the result differs from Debian's, is it explained by one of the
sections in @ref{Differences from Debian version sort}? If it is,
then this is not a bug -- please do not report it.

@item
If you have a question about specific ordering which is not explained
here, please write to @email{coreutils@@gnu.org}, and provide a
concise example that will help us diagnose the issue.

@item
If you still suspect a bug which is not explained by the above, please
write to @email{bug-coreutils@@gnu.org} with a concrete example of the
suspected incorrect output, with details on why you think it is
incorrect.

@end enumerate

@node Other version/natural sort implementations
@subsection Other version/natural sort implementations

As previously mentioned, there are multiple variations on
version/natural sort, each with its own rules. Some examples are:

@itemize

@item
Natural Sorting variants in
@uref{https://rosettacode.org/wiki/Natural_sorting,Rosetta Code}.

@item
Python's @uref{https://pypi.org/project/natsort/,natsort package}
(includes detailed description of their sorting rules:
@uref{https://natsort.readthedocs.io/en/master/howitworks.html,
natsort -- how it works}).

@item
Ruby's @uref{https://github.com/github/version_sorter,version_sorter}.

@item
Perl has multiple packages for natual and version sorts
(each likely with its own rules and nuances):
@uref{https://metacpan.org/pod/Sort::Naturally,Sort::Naturally},
@uref{https://metacpan.org/pod/Sort::Versions,Sort::Versions},
@uref{https://metacpan.org/pod/CPAN::Version,CPAN::Version}.

@item
PHP has a built-in function
@uref{https://www.php.net/manual/en/function.natsort.php,natsort}.

@item
NodeJS's @uref{https://www.npmjs.com/package/natural-sort,natural-sort package}.

@item
In zsh, the
@uref{http://zsh.sourceforge.net/Doc/Release/Expansion.html#Glob-Qualifiers,
glob modifier} @samp{*(n)} will expand to files in natural sort order.

@item
When writing C programs, the GNU libc library (@samp{glibc})
provides the
@uref{http://man7.org/linux/man-pages/man3/strverscmp.3.html,
strvercmp(3)} function to compare two strings, and
@uref{http://man7.org/linux/man-pages/man3/versionsort.3.html,versionsort(3)}
function to compare two directory entries (despite the names, they are
not identical to GNU Coreutils version sort ordering).

@item
Using Debian's sorting algorithm in:

@itemize
@item
python: @uref{https://stackoverflow.com/a/4957741,
Stack Overflow Example #4957741}.

@item
NodeJS: @uref{https://www.npmjs.com/package/deb-version-compare,
deb-version-compare}.
@end itemize

@end itemize


@node Related source code
@subsection Related source code

@itemize

@item
Debian's code which splits a version string into
@code{epoch/upstream_version/debian_revision} parts:
@uref{https://git.dpkg.org/cgit/dpkg/dpkg.git/tree/lib/dpkg/parsehelp.c#n191,
parsehelp.c:parseversion()}.

@item
Debian's code which performs the @code{upstream_version} comparison:
@uref{https://git.dpkg.org/cgit/dpkg/dpkg.git/tree/lib/dpkg/version.c#n140,
version.c}.

@item
Gnulib code (used by GNU Coreutils) which performs the version comparison:
@uref{https://git.savannah.gnu.org/cgit/gnulib.git/tree/lib/filevercmp.c,
filevercmp.c}.
@end itemize