Path.swift

Delightful, robust, cross-platform and chainable file-pathing functions.

mxcl
949
36
Swift

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A file-system pathing library focused on developer experience and robust end
results.

import Path

// convenient static members
let home = Path.home

// pleasant joining syntax
let docs = Path.home/"Documents"

// paths are *always* absolute thus avoiding common bugs
let path = Path(userInput) ?? Path.cwd/userInput

// elegant, chainable syntax
try Path.home.join("foo").mkdir().join("bar").touch().chmod(0o555)

// sensible considerations
try Path.home.join("bar").mkdir()
try Path.home.join("bar").mkdir()  // doesn’t throw ∵ we already have the desired result

// easy file-management
let bar = try Path.root.join("foo").copy(to: Path.root/"bar")
print(bar)         // => /bar
print(bar.isFile)  // => true

// careful API considerations so as to avoid common bugs
let foo = try Path.root.join("foo").copy(into: Path.root.join("bar").mkdir())
print(foo)         // => /bar/foo
print(foo.isFile)  // => true
// ^^ the `into:` version will only copy *into* a directory, the `to:` version copies
// to a file at that path, thus you will not accidentally copy into directories you
// may not have realized existed.

// we support dynamic-member-syntax when joining named static members, eg:
let prefs = Path.home.Library.Preferences  // => /Users/mxcl/Library/Preferences

// a practical example: installing a helper executable
try Bundle.resources.helper.copy(into: Path.root.usr.local.bin).chmod(0o500)

We emphasize safety and correctness, just like Swift, and also (again like
Swift), we provide a thoughtful and comprehensive (yet concise) API.

Sponsor @mxcl

Hi, I’m Max Howell and I have written a lot of open source software—generally
a good deal of my free time 👨🏻‍💻. Sponsorship helps me justify creating new open
source and maintaining it. Thank you.

Sponsor @mxcl.

Handbook

Our online API documentation covers 100% of our public API and is
automatically updated for new releases.

Codable

We support Codable as you would expect:

try JSONEncoder().encode([Path.home, Path.home/"foo"])

[
    "/Users/mxcl",
    "/Users/mxcl/foo",
]

Though we recommend encoding relative paths‡:

let encoder = JSONEncoder()
encoder.userInfo[.relativePath] = Path.home
encoder.encode([Path.home, Path.home/"foo", Path.home/"../baz"])

[
    "",
    "foo",
    "../baz"
]

Note if you encode with this key set you must decode with the key
set also:

let decoder = JSONDecoder()
decoder.userInfo[.relativePath] = Path.home
try decoder.decode(from: data)  // would throw if `.relativePath` not set

‡ If you are saving files to a system provided location, eg. Documents then
the directory could change at Apple’s choice, or if say the user changes their
username. Using relative paths also provides you with the flexibility in
future to change where you are storing your files without hassle.

Dynamic members

We support @dynamicMemberLookup:

let ls = Path.root.usr.bin.ls  // => /usr/bin/ls

We only provide this for “starting” function, eg. Path.home or Bundle.path.
This is because we found in practice it was easy to write incorrect code, since
everything would compile if we allowed arbituary variables to take any named
property as valid syntax. What we have is what you want most of the time but
much less (potentially) dangerous (at runtime).

Pathish

Path, and DynamicPath (the result of eg. Path.root) both conform to
Pathish which is a protocol that contains all pathing functions. Thus if
you create objects from a mixture of both you need to create generic
functions or convert any DynamicPaths to Path first:

let path1 = Path("/usr/lib")!
let path2 = Path.root.usr.bin
var paths = [Path]()
paths.append(path1)        // fine
paths.append(path2)        // error
paths.append(Path(path2))  // ok

This is inconvenient but as Swift stands there’s nothing we can think of
that would help.

Initializing from user-input

The Path initializer returns nil unless fed an absolute path; thus to
initialize from user-input that may contain a relative path use this form:

let path = Path(userInput) ?? Path.cwd/userInput

This is explicit, not hiding anything that code-review may miss and preventing
common bugs like accidentally creating Path objects from strings you did not
expect to be relative.

Our initializer is nameless to be consistent with the equivalent operation for
converting strings to Int, Float etc. in the standard library.

Initializing from known strings

There’s no need to use the optional initializer in general if you have known
strings that you need to be paths:

let absolutePath = "/known/path"
let path1 = Path.root/absolutePath

let pathWithoutInitialSlash = "known/path"
let path2 = Path.root/pathWithoutInitialSlash

assert(path1 == path2)

let path3 = Path(absolutePath)!  // at your options

assert(path2 == path3)

// be cautious:
let path4 = Path(pathWithoutInitialSlash)!  // CRASH!

Extensions

We have some extensions to Apple APIs:

let bashProfile = try String(contentsOf: Path.home/".bash_profile")
let history = try Data(contentsOf: Path.home/".history")

bashProfile += "\n\nfoo"

try bashProfile.write(to: Path.home/".bash_profile")

try Bundle.main.resources.join("foo").copy(to: .home)

Directory listings

We provide ls(), called because it behaves like the Terminal ls function,
the name thus implies its behavior, ie. that it is not recursive and doesn’t
list hidden files.

for path in Path.home.ls() {
    //…
}

for path in Path.home.ls() where path.isFile {
    //…
}

for path in Path.home.ls() where path.mtime > yesterday {
    //…
}

let dirs = Path.home.ls().directories
// ^^ directories that *exist*

let files = Path.home.ls().files
// ^^ files that both *exist* and are *not* directories

let swiftFiles = Path.home.ls().files.filter{ $0.extension == "swift" }

let includingHiddenFiles = Path.home.ls(.a)

Note ls() does not throw, instead outputing a warning to the console if it
fails to list the directory. The rationale for this is weak, please open a
ticket for discussion.

We provide find() for recursive listing:

for path in Path.home.find() {
    // descends all directories, and includes hidden files by default
    // so it behaves the same as the terminal command `find`
}

It is configurable:

for path in Path.home.find().depth(max: 1).extension("swift").type(.file).hidden(false) {
    //…
}

It can be controlled with a closure syntax:

Path.home.find().depth(2...3).execute { path in
    guard path.basename() != "foo.lock" else { return .abort }
    if path.basename() == ".build", path.isDirectory { return .skip }
    //…
    return .continue
}

Or get everything at once as an array:

let paths = Path.home.find().map(\.self)

Path.swift is robust

Some parts of FileManager are not exactly idiomatic. For example
isExecutableFile returns true even if there is no file there, it is instead
telling you that if you made a file there it could be executable. Thus we
check the POSIX permissions of the file first, before returning the result of
isExecutableFile. Path.swift has done the leg-work for you so you can just
get on with it and not have to worry.

There is also some magic going on in Foundation’s filesystem APIs, which we look
for and ensure our API is deterministic, eg. this test.

Path.swift is properly cross-platform

FileManager on Linux is full of holes. We have found the holes and worked
round them where necessary.

Rules & Caveats

Paths are just (normalized) string representations, there might not be a real
file there.

Path.home/"b"      // => /Users/mxcl/b

// joining multiple strings works as you’d expect
Path.home/"b"/"c"  // => /Users/mxcl/b/c

// joining multiple parts simultaneously is fine
Path.home/"b/c"    // => /Users/mxcl/b/c

// joining with absolute paths omits prefixed slash
Path.home/"/b"     // => /Users/mxcl/b

// joining with .. or . works as expected
Path.home.foo.bar.join("..")  // => /Users/mxcl/foo
Path.home.foo.bar.join(".")   // => /Users/mxcl/foo/bar

// though note that we provide `.parent`:
Path.home.foo.bar.parent      // => /Users/mxcl/foo

// of course, feel free to join variables:
let b = "b"
let c = "c"
Path.home/b/c      // => /Users/mxcl/b/c

// tilde is not special here
Path.root/"~b"     // => /~b
Path.root/"~/b"    // => /~/b

// but is here
Path("~/foo")!     // => /Users/mxcl/foo

// this works provided the user `Guest` exists
Path("~Guest")     // => /Users/Guest

// but if the user does not exist
Path("~foo")       // => nil

// paths with .. or . are resolved
Path("/foo/bar/../baz")  // => /foo/baz

// symlinks are not resolved
Path.root.bar.symlink(as: "foo")
Path("/foo")        // => /foo
Path.root.foo       // => /foo

// unless you do it explicitly
try Path.root.foo.readlink()  // => /bar
                              // `readlink` only resolves the *final* path component,
                              // thus use `realpath` if there are multiple symlinks

Path.swift has the general policy that if the desired end result preexists,
then it’s a noop:

  • If you try to delete a file, but the file doesn’t exist, we do nothing.
  • If you try to make a directory and it already exists, we do nothing.
  • If you call readlink on a non-symlink, we return self

However notably if you try to copy or move a file without specifying overwrite
and the file already exists at the destination and is identical, we don’t check
for that as the check was deemed too expensive to be worthwhile.

Symbolic links

  • Two paths may represent the same resolved path yet not be equal due to
    symlinks in such cases you should use realpath on both first if an
    equality check is required.
  • There are several symlink paths on Mac that are typically automatically
    resolved by Foundation, eg. /private, we attempt to do the same for
    functions that you would expect it (notably realpath), we do the same
    for Path.init, but do not if you are joining a path that ends up being
    one of these paths, (eg. Path.root.join("var/private')).

If a Path is a symlink but the destination of the link does not exist exists
returns false. This seems to be the correct thing to do since symlinks are
meant to be an abstraction for filesystems. To instead verify that there is
no filesystem entry there at all check if type is nil.

We do not provide change directory functionality

Changing directory is dangerous, you should always try to avoid it and thus
we don’t even provide the method. If you are executing a sub-process then
use Process.currentDirectoryURL to change its working directory when it
executes.

If you must change directory then use FileManager.changeCurrentDirectory as
early in your process as possible. Altering the global state of your app’s
environment is fundamentally dangerous creating hard to debug issues that
you won‘t find for potentially years.

I thought I should only use URLs?

Apple recommend this because they provide a magic translation for
file-references embodied by URLs, which gives you URLs like so:

file:///.file/id=6571367.15106761

Therefore, if you are not using this feature you are fine. If you have URLs the
correct way to get a Path is:

if let path = Path(url: url) {
    /*…*/
}

Our initializer calls path on the URL which resolves any reference to an
actual filesystem path, however we also check the URL has a file scheme first.

In defense of our naming scheme

Chainable syntax demands short method names, thus we adopted the naming scheme
of the terminal, which is absolutely not very “Apple” when it comes to how they
design their APIs, however for users of the terminal (which surely is most
developers) it is snappy and familiar.

Installation

SwiftPM:

package.append(
    .package(url: "https://github.com/mxcl/Path.swift.git", from: "1.0.0")
)

package.targets.append(
    .target(name: "Foo", dependencies: [
        .product(name: "Path", package: "Path.swift")
    ])
)

CocoaPods:

pod 'Path.swift', '~> 1.0.0'

Carthage:

Waiting on: @Carthage#1945.

Naming Conflicts with SwiftUI.Path, etc.

We have a typealias of PathStruct you can use instead.

Alternatives