check if given path is a subdirectory of another in golang

Issue

Say we have two paths:

c:\foo\bar\baz and c:\foo\bar

Is there any package/method that will help me determine if one is a subdirectory of another? I am looking at a cross-platform option.

Solution

You could try and use path.filepath.Rel():

func Rel(basepath, targpath string) (string, error)


Rel returns a relative path that is lexically equivalent to targpath when joined to basepath with an intervening separator.
That is, Join(basepath, Rel(basepath, targpath)) is equivalent to targpath itself

That means Rel("c:\foo\bar", "c:\foo\bar\baz") should be baz, meaning a subpath completely included in c:\foo\bar\baz, and without any ‘../‘.
The same would apply for unix paths.

That would make c:\foo\bar\baz a subdirectory of c:\foo\bar.