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Alex Rupérez

Published: 15 Jan 14:09
I starred mxcl/swift-sh at GitHub.
Easily import third-party dependencies in your Swift scripts
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Writing Swift scripts is easy:

$ cat <<EOF > script
$ chmod u+x script
$ ./script

Sadly, to use third-party dependencies we have to migrate our script to a swift package and use swift build, a relatively heavy solution when all we wanted was to whip up a quick script. swift-sh gives us the best of both worlds:

$ cat <<EOF > script
#!/usr/bin/swift sh
import PromiseKit  // @mxcl ~> 6.5
$ chmod u+x script
$ ./script

In case it’s not clear, swift-sh reads the comment after the import and uses this information to fetch your dependencies.

Let’s work through an example: if you had a single file called foo.swift and you wanted to import mxcl/PromiseKit:

#!/usr/bin/swift sh

import Foundation
import PromiseKit  // @mxcl ~> 6.5

firstly {
}.then {
}.done {
    print("notice: two and a half seconds elapsed")

You could run it with:

$ swift sh foo.swift

Or to make it more “scripty”, first make it executable:

$ chmod u+x foo.swift
$ mv foo.swift foo    # optional step!

And then run it directly:

$ ./foo

Support mxcl

Hey there, I’m Max Howell. I’m a prolific producer of open source software and probably you already use some of it (for example, I created brew). I work full-time on open source and it’s hard; currently I earn less than minimum wage. Please help me continue my work, I appreciate it 🙏🏻

Other ways to say thanks.


brew install mxcl/made/swift-sh

We’re in core now, but I’m not updating it, so I still recommend my tap above. If you prefer though you can use the core formula:

brew install swift-sh

Or with Mint:

mint install mxcl/swift-sh

Or you can build manually using swift build.

Installation results in a single executable called swift-sh, the swift executable will call this (provided it is in your PATH) when you type: swift sh.

We actively support both Linux and Mac and will support Windows as soon as it is possible to do so.


Add the shebang as the first line in your script: #!/usr/bin/swift sh.

Your dependencies are determined via your import lines:

#!/usr/bin/swift sh
import AppUpdater    // @mxcl
// ^^, latest version

import PromiseKit    // @mxcl ~> 6.5
// ^^ mxcl/PromiseKit, version 6.5.0 or higher up to but not including 7.0.0 or higher

import Chalk         // @mxcl == 0.3.1
// ^^ mxcl/Chalk, only version 0.3.1

import LegibleError  // @mxcl == b4de8c12
// ^^ mxcl/LegibleError, the precise commit `b4de8c12`

import Path          // mxcl/Path.swift ~> 0.16
// ^^ for when the module-name and repo-name are not identical

import BumbleButt    // ~> 9
// ^^ non-GitHub URLs are fine

import CommonTaDa    // ~> 1
// ^^ ssh URLs are fine

import TaDa          // ssh:// ~> 1
// ^^ this style of ssh URL is also fine

import Foo  // ./my/project
import Bar  // ../my/other/project
import Baz  // ~/my/other/other/project
import Fuz  // /I/have/many/projects
// ^^ local dependencies must expose library products in their `Package.swift`
// careful: `foo/bar` will be treated as a GitHub dependency; prefix with `./`
// local dependencies do *not* need to be versioned

import Floibles  // @mxcl ~> 1.0.0-alpha.1
import Bloibles  // @mxcl == 1.0.0-alpha.1
// ^^ alphas/betas will only be fetched if you specify them explicitly like so
// this is per Semantic Versioning guidelines

swift-sh reads the comments after your imports and fetches the requested SwiftPM dependencies.

It is not necessary to add a comment specification for transitive dependencies.

Editing in Xcode

The following will generate an Xcode project (not in the working directory, we keep it out the way in our cache directory) and open it, edits are saved to your script file.

$ swift sh edit ./myScript


Converting your script to a package

Simple scripts can quickly become bigger projects that would benefit from being packages that you build with SwiftPM. To help you migrate your project we provide swift sh eject, for example:

$ swift sh eject foo.swift

creates a Swift package in ./Foo, from now on use swift build in the Foo directory. Your script is now ./Foo/Sources/main.swift.

Use in CI

If you want to make scripts available to people using CI; use stdin:

brew install mxcl/made/swift-sh
swift sh <(curl arg1 arg2

Internal Details

swift sh creates a Swift Package.swift configured to fetch your dependencies and build a single executable for your script in ~/Library/Developer/swift-sh.cache†, the script is then executed via swift run.

† We use the FreeDesktop specified cache location on Linux.

Swift Versions

swift-sh uses the active tools version, (ie: xcode-select) or whichever Swift is first in the PATH on Linux. It writes a manifest for the package it will swift build with that tools-version. Thus Xcode 10.1 builds a script with Swift 4.2, Xcode 10.2 builds with Swift 5. Dependencies build with the Swift versions they declare support for, provided the active toolchain can do that (eg. Xcode 10.1 supports Swift 3.4, 4.0 and 4.2, Xcode 10.2 supports Swift 4.0, 4.2 and 5.0).

To declare a support for specific Swift versions in your script itself, use #if swift or #if compiler directives.


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error: unable to invoke subcommand: /Applications/

If you got here via Google, you have a script that uses this tool, if you now install swift-sh, you will be able to run your script:

brew install mxcl/made/swift-sh

Or see the above installation instructions.