The iOS emulator is deceptively powerful. Learn about its C.L.I. to automate all sorts of things.
I remember the day I first ran a command in Terminal. At that moment, I truly felt like a bonafide programmer. With my fellow students huddled around my laptop at college, I swiftly pecked out a command with steadfast confidence while acting as if I'd done it a million times before.
For the modern iOS developer, spending time in Terminal and firing up the shell of choice on macOS, Bash, is commonplace. Today, we'll look at a utility one can use in Terminal that's been around for a few years but has largely eluded the spotlight:
simctl — a lovely little tool to aid with the iOS simulator.
So, what is it? First released alongside Xcode 6, simctl is a command-line utility (itself housed within xcrun) that can be used in Terminal to do all sorts of helpful things with the iOS simulator. It supports simple tasks such as device book keeping to more immediate time savers such as recording video.
This simple C.L.I. wrapper essentially parlays the power of Xcode's tools over to Terminal. Though they are available for individual download, in the modern era we simply have them included as part of the Xcode package.
Betas Gonna Beta
With iOS 11 knocking at our doorstep, and Xcode 9 currently fending off bugs — if you're playing along today, I find it incumbent to ensure you're using Xcode 8.3.3's tools:
xcode-select --print-path # If that doesn't include Xcode-Beta in it, all clear
With most development environments, that should produce something like this:
If you currently using Xcode 9's tools, making a switch is trivial:
sudo xcode-select -switch (the path to Xcode)/Xcode.app
That said, let's peek at what simctl can bring to the table.
Less Quicktime, More Terminal
One of my favorite uses of simctl is to capture a quick video from the iOS simulator. If you're devin' on some new features and want to put it out on the Twittersphere, or simply need a visual aid to show a product owner or Q.A. — one command can get you there:
xcrun simctl io booted recordVideo (filename).(extension)
When used, a high fidelity recording begins capturing everything on the main framebuffer display of the simulator. When you're ready to stop, simply return to Terminal and enter CTRL+C.
Feel free to save files as either a .mov, .h264, .mp4 or .fmp4. The opportunity is there to think outside the box, too. Take, for instance, the ability to replace a file destination with a URL to establish a server socket to pipe video over
The equivalent does exist for screenshots as well, with built in support for .png, .tiff, .bmp, .gif and .jpeg:
xcrun simctl io booted screenshot myScreenShot.png
But, hey — CMD+S it just a bit easier sooooo ¯\(ツ)/¯.
The perceptive reader may have noticed the "booted" argument used in the previous commands. All of simctl's sub commands have a device parameter, and each device ran via the simulator has its own UDID. To view these yourself, feel free to employ — what else — a simctl command:
xcrun simctl list
This produces a comprehensive list of of device pairs, types, their availability and runtimes available for the simulator to use. On mine, I can clearly see the iPhone 5 I've got currently running among the output:
iPhone 5 (D1F67F00-FA3D-42B7-9E2F-FEF23809D4A0) (Booted)
That means I could just as well take a screenshot with simctl by supplying its UDID for the device parameter:
xcrun simctl io D1F67F00-FA3D-42B7-9E2F-FEF23809D4A0 screenshot screen.png
As you've likely concluded, passing "booted" for the device argument automatically supplies the booted device's UDID on our behalf. If there is more than one device running, simctl will just pick one of them.
For the remainder of this article, I'll use booted where the device parameter is expected.
iOS Developer, and Doctor
Let's face it, nobody likes log files. Developers ask for them, consumers have no idea what they are and when we do use them they are usually bereft of useful formatting or digestible text.
But yet, as developers we just can't stop #loggingallthethings. Usually for good reason, too. That said, I'd be remiss if I didn't mention you can generate an incredibly detailed log of anything that's happened in your simulator session with simctl:
xcrun simctl diagnose
After you move past the wall of text warning you that the dump contains only your personal information, iCloud Accounts, Apple ID, name, user name, email address and settings, file paths, downloads, IP addresses, network connection information and installed applications — what you find has some neat stuff in it:
- System Logs
- Simulator Logs
- Device and Environment .plist settings
- And a whole load of more information
But, yes — buyer beware. Keep that log stashed locally unless the idea of a total stranger standing over your shoulder while you use a MacBook doesn't frighten you at all.
Another increasingly common part of iOS development is testing url schemes. With deep linking becoming a powerful tool to incorporate both as a consumer and a provider, simctl can help here too:
xcrun simctl openurl booted https://www.dreaminginbinary.co/
And just like that, the active device pops open Safari with the URL. Of course, if you know other app's schemes — those are fair game, too:
xcrun simctl openurl booted sms: #Open Messages
Though that previous commands simply opens messages, parameters are fully supported as well. For example, if you wanted to send yours truly a text message — fire away:
xcrun simctl openurl booted sms:1-417-323-2345
This demonstrates two things
- The flexibility of simctl
- And a fake phone number
Odds and Ends
Though simctl has a robust toolset that's worth your time, here are some other quick hitters of some of my personal highlights:
xcrun simctl addmedia booted (path to file, or files)
Printing Environment Variables
xcrun simctl getenv booted (variable name)
Forcing an iCloud Sync
xcrun simctl icloud_sync booted
Reset Device Content and Settings
xcrun simctl erase booted
Install an App On Device
xcrun simctl install booted (The path to the app)
…And Launching Apps (via bundle ID)
xcrun simctl launch booted (ID)
There is quite a lot of pieces here for us to mash together to pull off some truly capable workflows. You can even create your own custom simulator, as Erica Sadun outlines in detail here. Be sure to study the whole list of things it can do for you:
xcrun simctl -help
Short and Sweet
While not directly related to simctl, it's worth noting that you can employ some syntactical sugar to simctl's commands, if you will, in the form of an alias. For the uninitiated, this allows one to circumvent longer commands in lieu of a shorter, more personalized one:
xcrun simctl list #List all simulator devices
can become something like
Doing so requires just a hop, skip and step around your local bash profile. Dropping an alias definition here will ensure one can use it time and time again between terminal sessions. Otherwise, alias definitions are scoped to the current terminal process:
nano ~/.bash_profile #Or any other text editor... #For example, with Xcode: open -a Xcode ~/.bash_profile
Then, simply define your alias and save it. In the beloved Nano, this is simply executed as such:
alias simDevices="xcrun simctl list" # Hit CMD+O to save # Then CMD+X to exit # Profit from shorter commands like a boss
Of note, Bash alias' don't have the luxury of accepting parameters. If you yearn to record a video with simctl as previously mentioned, but with the allure of shorter commands — one would need to define a function instead. In this case, it would facilitate the parameterization of the recording's file name.
While command line utilities aren't the heroes of iOS development, it cannot be argued that they are indeed useful. Bolstering our tool belt as software engineers cannot be understated. Much like buying insurance, it's not so incredible day in and day out — until the day comes when you really need it.
Now, if you'll excuse me, I'm off to…
xcrun simctl openurl N789YE9Q-3TSV-9083-B314-A3NBS64GOP90 http://bit.ly/weekend_planz
Until next time