30.2.1 Version-sort ordering rules

The version sort ordering rules are:

  1. The strings are compared from left to right.
  2. First the initial part of each string consisting entirely of non-digit bytes is determined.
    1. These two parts (either of which may be empty) are compared lexically. If a difference is found it is returned.
    2. The lexical comparison is a lexicographic comparison of byte strings, except that:
      1. ASCII letters sort before other bytes.
      2. A tilde sorts before anything, even an empty string.
  3. 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.
    1. For these purposes an empty string (which can only occur at the end of one or both version strings being compared) counts as zero.
    2. Because the numerical value is used, non-identical strings can compare equal. For example, ‘123’ compares equal to ‘00123’, and the empty string compares equal to ‘0’.
  4. 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.

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

foo  vs  foo   (rule 2, non-digits)
07   vs  7     (rule 3, digits)
.    vs  a.    (rule 2)
7    vs  7     (rule 3)
z    vs  z     (rule 2)

Comparison flow based on above algorithm:

  1. The first parts (‘foo’) are identical.
  2. The second parts (‘07’ and ‘7’) are compared numerically, and compare equal.
  3. The third parts (‘.’ vs ‘a.’) are compared lexically by ASCII value (rule 2.B).
  4. The first byte of the first string (‘.’) is compared to the first byte of the second string (‘a’).
  5. Rule 2.B.a says letters sorts before non-letters. Hence, ‘a’ comes before ‘.’.
  6. The returned result is that foo7a.7z comes before foo07.7z.

Result when using sort:

$ cat input3
$ sort -V input3

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