GNU coreutils’ version sort algorithm implements specialized handling of file extensions (or strings that look like file names with extensions).
This nuanced implementation enables slightly more natural ordering of files.
The additional rules are:
Examples for rule 1:
hello-8.txt: the suffix is
hello-8.2.txt: the suffix is
.2’ is not included because the dot is not followed by a letter)
hello-8.0.12.tar.gz: the suffix is
.0.12’ is not included)
hello-8.2: no suffix (suffix is an empty string)
hello.foobar65: the suffix is
gcc-c++-10.8.12-0.7rc2.fc9.tar.bz2: the suffix is
.7rc2is not included as it begins with a digit)
Examples for rule 2:
.txtsuffix is temporarily removed from both strings.
foo-10.tar.xz, the suffixes
.tar.xzare temporarily removed from the strings.
Example for rule 3:
hello.foobar4, the suffixes (
.foobar4) are temporarily removed. The remaining strings are identical (
hello). The suffixes are then restored, and the entire strings are compared (
Examples for rule 4:
hello-8.10.txt, the suffixes (
.txt) are temporarily removed. The remaining strings (
hello-8.10) are compared as previously described (
hello-8.2comes first). (In this case the suffix removal algorithm does not have a noticeable effect on the resulting order.)
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:
hello- vs hello- (rule 2, all non-digit characters) 8 vs 8 (rule 3, all digit characters) .txt vs . (rule 2) empty vs 2 empty vs .txt
The comparison of the third parts (‘
.txt’) will determine that the shorter string comes first -
resulting in hello-8.2.txt appearing first.
Indeed this is the order in which Debian’s
dpkg compares the strings.
A more natural result is that hello-8.txt should come before hello-8.2.txt, and this is where the suffix-removal comes into play:
The suffixes (
.txt) are removed, and the remaining strings are
broken down into the following parts:
hello- vs hello- (rule 2, all non-digit characters) 8 vs 8 (rule 3, all digit characters) empty vs . (rule 2) empty vs 2
As empty strings sort before non-empty strings, the result is
A real-world example would be listing files such as: gcc_10.fc9.tar.gz and gcc_10.8.12.7rc2.fc9.tar.bz2: Debian’s algorithm would list gcc_10.8.12.7rc2.fc9.tar.bz2 first, while ‘ls -v’ will list gcc_10.fc9.tar.gz first.
These priorities make sense for ‘ls -v’: Versioned files will be listed in a more natural order.
For ‘sort -V’ these priorities might seem arbitrary. However,
because the sorting code is shared between the
program, the ordering rules are the same.