什么是“规范路径”？

因此，绝对路径是到达某个文件或位置的一种方式，这个文件或位置描述了到达它的完整路径、完整路径以及它依赖于操作系统(例如，Windows 和 Linux 的绝对路径是不同的)。另一方面，相对路径是从当前位置 ..(两个点)描述的文件或位置的路由，指示目录树中的上级级别。这一点我几年来一直很清楚。

当搜索我甚至看到有规范化的文件了！ 我所知道的就是 CANONICAL 的意思是“根据规则”之类的东西。

有没有人能给我一些关于规范事物的理论方面的启示？

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The whole point of making anything "canonical" is so that you can compare two things. For example, both ../../here/bar/x and ./test/../../bar/x may refer to the same location, but you can't do a textual comparison on the two paths. However, if you turn them into their canonical representation, they both become ../bar/x, and we see that they actually refer to the same thing.

In short, it is often the case that you have many ways of referring to one thing, and in that case you may be able to define a canonical representation which is unique and which allows you to get a handle on col­lections of such things.

(If you're looking for more examples, all of mathematics is full of "canonical" constructions for all sorts of objects, and very much with the same purpose in mind. Maybe this Wikipedia article can provide some ad­ditional directions.)

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A good way to define a canonical path will be: the shortest absolute path (short, in the meaning of string-length).

This is an example of the difference between an absolute path and a canonical path:

absolute path: C:\abc\..\abc\file.txt
canonical path: C:\abc\file.txt

Canonicalization is a type of normalization which allows an object to be identified in a unique way. A relative path cannot do it, by definition.

For more info:

https://en.wikipedia.org/wiki/Canonicalization

https://en.wikipedia.org/wiki/Canonical_form

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What a canonical path is (or its difference from an absolute path) is system dependent.
Typically if a (full) path contains aliases, shortcuts or symbolic links the canonical path resolves all these into the actual directories they refer.
Example: if /bin/a is a sym link, you can find it anywhere you request for an absolute path e.g. from java.io.File#getAbsolutePath while the real file (i.e. the actual target of the link) i.e. usr/local/bin/a would be return as a canonical path e.g. from java.io.File#getCanonicalPath

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The most issues with canonical paths occur when you are passing the name of a dir and not file. For file, if we are providing absolute path that is also the canonical path. But for dir it means omitting the last "/". For example, "/var/tmp/foo" is a canonical path while "/var/tmp/foo/" is not.

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A good definition of a canonical path is given in the documentation of readlink in GNU Coreutils. It is specified that 'Canonicalize mode' returns an equivalent path that doesn't have any of these things:

  1. hard links to self (.) and parent (..) directories
  2. repeated separators (/)
  3. symbolic links

The string length is irrelevant, as is demonstrated in the following example.

You can experiment with readlink -f (canonicalize mode) or its preferred equivalent command realpath to see the difference between an 'absolute path' and a 'canonical absolute path' for some programs on your system if you are running linux or are using GNU Coreutils.

I can get the path of 'java' on my system using which

$ which java
/usr/bin/java

This path, however, is actually a symbolic link to another symbolic link. This symbolic link chain can be displayed using namei.

$ namei $(which java)
f: /usr/bin/java
d /
d usr
d bin
l java -> /etc/alternatives/java
d /
d etc
d alternatives
l java -> /usr/lib/jvm/java-17-openjdk-amd64/bin/java
d /
d usr
d lib
d jvm
d java-17-openjdk-amd64
d bin
- java

The canonical path can be found using the previously mentioned realpath command.

$ realpath $(which java)
/usr/lib/jvm/java-17-openjdk-amd64/bin/java

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