快速相当于Ruby的"Pathname.relative_path_from“

Question

Ruby的从…文档。

在objc中，已经有了KSFileUtilities的stringRelativeToURL方法，这非常接近。我正在寻找一种能够在Linux上运行的纯快速解决方案。

我更喜欢使用file:// URL的解决方案，但String也不错。

文件系统可以区分大小写/不区分大小写。确定相对路径可能比较棘手。

投入和预期产出实例：

| Long Path                      | Relative to Path | Return Value      |
|--------------------------------|------------------|-------------------|
| /usr/X11/agent/47.gz           | /usr/X11         | agent/47.gz       |
| /usr/share/man/meltdown.1      | /usr/share/cups  | ../man/meltdown.1 |
| file:///var/logs/x/y/z/log.txt | file:///var/logs | x/y/z/log.txt     |

Swift已经有了：：其中:在：)，但是它不返回相对路径。

Answer 1

据我所知，Swift标准库或基金会框架中没有这样的方法。

下面是作为URL扩展方法的一种可能实现

extension URL {
    func relativePath(from base: URL) -> String? {
        // Ensure that both URLs represent files:
        guard self.isFileURL && base.isFileURL else {
            return nil
        }

        // Remove/replace "." and "..", make paths absolute:
        let destComponents = self.standardized.pathComponents
        let baseComponents = base.standardized.pathComponents

        // Find number of common path components:
        var i = 0
        while i < destComponents.count && i < baseComponents.count
            && destComponents[i] == baseComponents[i] {
                i += 1
        }

        // Build relative path:
        var relComponents = Array(repeating: "..", count: baseComponents.count - i)
        relComponents.append(contentsOf: destComponents[i...])
        return relComponents.joined(separator: "/")
    }
}

我的测试代码：

func test(_ p1: String, _ p2: String) {
    let u1 = URL(fileURLWithPath: p1)
    let u2 = URL(fileURLWithPath: p2)
    print(u1.relativePath(from: u2) ?? "<ERROR>")
}
test("/usr/X11/agent/47.gz",      "/usr/X11")        // "agent/47.gz"
test("/usr/share/man/meltdown.1", "/usr/share/cups") // "../man/meltdown.1"
test("/var/logs/x/y/z/log.txt",   "/var/logs")       // "x/y/z/log.txt"

备注：

• ".“还有“.”在给定的URL中，删除相对文件URL，并将相对文件URL变为绝对URL(都使用standardized方法URL)。
• 不处理大小写敏感性。
• 假定基本URL表示一个目录。

增编：@neoneye将其包装成一个Swift包：SwiftyRelativePath。

Answer 2

马丁·R得到了正确的答案。但是，当基本URL本身是一个文件时，我遇到了一个问题。因此，我做了一些调整：

func relativePath(from base: URL) -> String? {
    // Ensure that both URLs represent files:
    guard self.isFileURL && base.isFileURL else {
        return nil
    }

    //this is the new part, clearly, need to use workBase in lower part
    var workBase = base
    if workBase.pathExtension != "" {
        workBase = workBase.deletingLastPathComponent()
    }

    // Remove/replace "." and "..", make paths absolute:
    let destComponents = self.standardized.resolvingSymlinksInPath().pathComponents
    let baseComponents = workBase.standardized.resolvingSymlinksInPath().pathComponents

    // Find number of common path components:
    var i = 0
    while i < destComponents.count &&
          i < baseComponents.count &&
          destComponents[i] == baseComponents[i] {
            i += 1
    }

    // Build relative path:
    var relComponents = Array(repeating: "..", count: baseComponents.count - i)
    relComponents.append(contentsOf: destComponents[i...])
    return relComponents.joined(separator: "/")
}

我的测试用例有点扩展了。案例4是我引发这一小变化的诱因。

 func testRelativePath() {
    // This is an example of a functional test case.
    // Use XCTAssert and related functions to verify your tests produce the correct results.
    func test(_ p1: String, _ p2: String,_ result: String,_ nr: Int) {
        let u1 = URL(fileURLWithPath: p1)
        let u2 = URL(fileURLWithPath: p2)
        let r = u1.relativePath(from: u2)!
        XCTAssert( r == result,"\(nr): '\(r)' != '\(result)'")
    }
    test("/usr/X11/agent/47.gz",      "/usr/X11","agent/47.gz", 1)
    test("/usr/share/man/meltdown.1", "/usr/share/cups", "../man/meltdown.1",2 )
    test("/var/logs/x/y/z/log.txt",   "/var/logs", "x/y/z/log.txt",3)
    test("/usr/embedded.jpg",   "/usr/main.html", "embedded.jpg",4)
    test("/usr/embedded.jpg",   "/usr", "embedded.jpg",5)
    test("~/Downloads/resources",   "~/", "Downloads/resources",6)
    test("~/Downloads/embedded.jpg",   "~/Downloads/main.html", "embedded.jpg",7)
    test("/private/var/logs/x/y/z/log.txt", "/var/logs", "x/y/z/log.txt",8)
 }

Answer 3

我正在使用Kneup向导的版本，但是当基本dir有一个扩展时出现了问题。因此，我添加了代码来检查路径是否存在，并且是dir。

public extension URL 
{
    func relativePath(from base: URL) -> String?
    {
        // Ensure that both URLs represent files:
        guard self.isFileURL &&
              FileManager.default.fileExists(atPath: self.path) else
        {
            NSLog("self is not a fileURL or it does not exists")
            return nil
        }

        var isDir = ObjCBool(true)
        guard FileManager.default.fileExists(atPath: base.path, isDirectory: &isDir) &&
              isDir.boolValue else
        {
            NSLog("base is not a directory or it does not exists")
            return nil
        }           


        // Remove/replace "." and "..", make paths absolute:
        let destComponents = self.resolvingSymlinksInPath().pathComponents
        let baseComponents = base.resolvingSymlinksInPath().pathComponents

        // Find number of common path components:
        let i = Set(destComponents).intersection(Set(baseComponents)).count

        // Build relative path:
        let relComponents = Array(repeating: "..", count: baseComponents.count - i) +
                            destComponents[i...]
        return relComponents.joined(separator: "/")
    }
}