`swift sh`

Writing Swift scripts is easy:

$ cat <<EOF > script
#!/usr/bin/swift
print("Hi!")
EOF
$ chmod u+x script
$ ./script
Hi!

However often we need dependencies, achieving this is… tedious. But not anymore:

$ cat <<EOF > script
#!/usr/bin/swift sh
import PromiseKit  // @mxcl ~> 6.5
print(Promise.value("Hi!"))
EOF
$ chmod u+x script
$ ./script
Promise(value: "Hi!")

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 that needed to import mxcl/PromiseKit:

#!/usr/bin/swift sh

import PromiseKit  // @mxcl ~> 6.5

firstly {
    URLSession.shared.dataTask(.promise, with: url)
}.then {
    after(.seconds(2))
}.done {
    print("Scripts with package dependencies!")
    exit(0)
}

RunLoop.main.run()

You could run it with:

$ swift sh foo.swift

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

$ chmod u+x foo.swift

And then run it directly:

$ ./foo.swift

Installation

brew install mxcl/made/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.

Support mxcl

Hi, I’m Max Howell and I have written a lot of open source software, and probably you already use some of it (Homebrew anyone?). Please help me so I can continue to make tools and software you need and love. I appreciate it x.

Donate to my Patreon.

Usage

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 PromiseKit  // @mxcl ~> 6.5
import Foo         // @bar == 6.5
import Baz         // @bar == b4de8c
import Floobles    // mxcl/Flub == master
import BumbleButt  // https://example.com/bb.git ~> 9

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

The above will fetch:

https://github.com/mxcl/PromiseKit, the highest available version that is greater than or equal to 6.5.0 but less than 7.0.0
https://github.com/bar/Foo version precisely 6.5.0
https://github.com/bar/Baz, with the specific Git SHA b4de8c
https://github.com/mxcl/Flub, master branch
https://example.com/bb.git, largest version between 9.0.0 and 10.0.0

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

Internal Details

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

TODO

Specifications for GitHub packages where the import name is not the same as the repository name
More types of version specifications
Removing SwiftPM output unless there are errors
Optimizing the cache (creating a library structure more like gem or pip would)
Error out if the import specification is invalid, currently we silently ignore such lines

Limitations

Our logic for determining package modules is insufficient. It works for most packages, but will fail for packages with multiple modules. I’ll fix this once I need to, but feel free to PR it. Doing this properly is probably easiest if we depend on SwiftPM itself and use its machinery to get module information.

Alternatively we could require all imports that a script depends on to be specified in the form that we already do. Or we could assume all imports that are not Apple imports to be dependencies for the generated Package.swift. Or we could manage the build ourselves which isn’t too hard and would be the solution that simplifies our system the most.

If you have two scripts with the same name we will (currently) always need to rebuild whenever you rotate between them.

Alternatives

`error: unable to invoke subcommand: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-sh`

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

brew install mxcl/made/swift-sh

Or see the above installation instructions.