Scripting OS X

In one of the recent betas for macOS 11.0 Big Sur, the xpath command line tool changed. Big Sur uses the 5.28 version of the tool, while Catalina defaults to the 5.18 version.

These aren’t version numbers for xpath but actually version numbers for perl. When you look at all the xpath executables you will see that they are actually perl scripts.

> head -n1 /usr/bin/xpath*
==> /usr/bin/xpath <==
#!/usr/bin/perl

==> /usr/bin/xpath5.18 <==
#!/usr/bin/perl5.18 -w

==> /usr/bin/xpath5.28 <==
#!/usr/bin/perl5.28

The perl environment will choose the xpath script ending in the version number matching the perl version automatically. The plain xpath script with no version number serves as fallback.

Either way, Catalina runs perl 5.18 and xpath5.18 and Big Sur runs perl 5.28 and the newer xpath5.28 script.

The problem here is that the newer xpath script has a different syntax:

[5.18] xpath [filename] query
[5.28] xpath [options] -e query [-e query...] [filename...]

Either version will use stdin when there is no file name, but the newer xpath requires the query string to be labeled with a -e argument.

So, your scripts that are using the xpath tool to parse XML data, will fail in Big Sur!

The easiest fix is to change the script to use the new syntax, i.e. insert the -e at the right place and if necessary re-arrange the arguments. But then the script will fail on older versions of macOS. Many of us will have to write our scripts to be able to support the latest and older versions of macOS for a transition time. For some MacAdmins the transition time can be several years.

Since Big Sur still includes xpath5.18, another solution is to just hardcode the version whenever you use xpath. But this will only defer the problem to a future version of macOS, when the 5.18 version of the script is removed.

A better solution is to check the version of macOS that is being used and to call xpath with the proper for each version:

    if [[ $(sw_vers -buildVersion) > "20A" ]]; then
        xpath -e "//query" "/path/to/file"
    else
        xpath "/path/to/file" "//query" 
    fi

This will call xpath with the new syntax on Big Sur (20A) and higher and use the older syntax otherwise. (Why I use the build version.)

If you are using xpath in multiple locations in a script, using this code everywhere will become tedious. In the Installomator script, we often use xpath to parse the download URL out of an XML file. As of now, there are nine occurences of xpath, but as more people contribute to Installomator, this is likely to go up.

There is a nice sleight-of-hand trick you can use to make the script resilient to change in Big Sur, without having to touch every use of xpath in the code.

At the beginning of the script (before the first use of xpath) insert this function:

xpath() {
    # the xpath tool changes in Big Sur 
    if [[ $(sw_vers -buildVersion) > "20A" ]]; then
        /usr/bin/xpath -e "$@"
    else
        /usr/bin/xpath "$@"
    fi
}

Since the shell interpreter (bash or zsh) will prefer a local function over an external executable, this function will now be used for all uses of xpath in the remaining code. We don’t need to touch them at all.

Within the function, we tell the interpreter to use the executable by using its full path.

In Installomator, we pipe data into xpath, so there are no files involved and the above works fine.

When you use xpath with files, it gets a bit more complicated, because the order of the arguments changed between the versions.

With the assumption that the current use is xpath [filename] query we can use the following:

xpath() { # [filename] query
    # xpath in Big Sur changes syntax
    if [[ -n $2 ]]; then
        local query=$2
        local filename=$1
    else 
        local query=$1
        local filename=""
    fi

    if [[ $(sw_vers -buildVersion) > "20A" ]]; then
        /usr/bin/xpath -e "$query" "$filename"
    else
        /usr/bin/xpath "$filename" "$query"
    fi
}

You will want to make a note for some point in the future, when you finally can drop Catalina support, to revisit these scripts and clean them up for the new syntax.

I have not yet encountered other command line tools that change in a similar way in Big Sur. If you do, you should be able to use a similar function to simplify the transtition.

When you do, let us know in the comments!

I had been fairly busy with both the JNUC and MacSysAdmin presentations, but work on Installomator has continued.

I also did an overview of what Installomator does in my MacSysAdmin Online presentation: “Practical Scripting”.

Many of these new features have been provided from others, either through GitHub issues, pull requests, or through comments in the #installomator channel on MacAdmins Slack. Thanks to all who contributed.

What’s new in v0.4:

• you can now set script variables as an argument in the form VARIABLE=value. More detail on this in the README file, ‘Configuration from Arguments.’
• change downloadFromGit to match file types better
• implemented a workaround for changed behavior of xpath in Big Sur
• added an option prompt_user_the_kill to BLOCKING_PROCESS_ACTION which will kill the process after the third unsuccessful attempt to quit
• added several new labels for total of 116

Get the script and find the instructions on the GitHub repo.

If you have any feedback or questions, please join us in the #installomatorchannel on MacAdmins Slack.

Thanks again to all those who contributed!

We got the expected new iPhones 12 this week, all four models, and a new HomePod mini. I am actually looking forward to a smaller iPhone 12 mini to replace my iPhone X.

In other (some would say good) news, macOS 11 Big Sur was not released this week, but we got beta 10 instead. There is an expectation for another Apple event introducing the first Apple Silicon based Macs in the upcoming weeks and that would be an obvious time to release Big Sur to everyone.

If you would rather get the weekly newsletter by email, you can subscribe to the Scripting OS X Weekly Newsletter here!! (Same content, delivered to your Inbox once a week.)

News and Opinion

• Jamf and Google announce conditional access partnership preview – Jamf

macOS 11 Big Sur, Apple Silicon, and iOS 14

• Mac Transition to Apple Silicon – Mr. Macintosh
• Apple on designing the A14 Bionic for the iPad Air and beyond – Chris Velazco, Engadget
• iOS and iPadOS 14: The MacStories Review – Federico Viticci, MacStories
• What’s New in macOS Big Sur 11 Beta 10 (20A5395g)? – Mr Macintosh
• Building a macOS Big Sur beta VM with VMware Fusion 12 – Mod Titan

MacAdmins on Twitter

• Taha Karim: “MacOS Ransomware in one tweet” (Thread, via Mat X)
• William Smith: “Tomorrow (October 13, 2020): Support for Microsoft Office 2016 for Mac — any version 16.16.x and lower— ends. No more software updates to fix: • Bugs • Compatibility problems • Security vulnerabilities – No macOS Big Sur support”

Bugs and Security

• Converting Unified Logs – A Great Disturbance In The Force – Sarah Edwards
• How does your Mac know when Apple revokes a developer certificate? – Howard Oakley

Support and HowTos

• Jamf Connect 2.0 and ADFS – Frederick Abeloos
• Jamf Connect with ADFS Federation and AllowCloudPasswordValidation – Frederick Abeloos
• Solving a Difficult Package – Tony Williams
• Faster way to download and install Xcode – Igor Kulman
• Managing Network Printers with Jamf Computer Policies and Self Service Policies – Caine Hörr, Jamf Nation
• How macOS schedules and dispatches background tasks using CTS 1 – Howard Oakley (Part 2, Part 3

Scripting and Automation

• bash Errors – Julia Evans, Wizard Zines

Updates and Releases

• LuLu 2.0 beta
• Jamf Pro 10.25
• BBEdit 13.5
• Announcing 9 New Profiles, Choose a Time for App & OS Updates, and More – Kandji Blog

To Watch

• Using a debugger with scripting languages on macOS – Tim Perfitt
• Jamf Nation User Conference 2020 – Session videos on YouTube

To Listen

• The MSP Toolchain with Ryan Grimes – Mac Admins Podcast
• Vote for DevOps – MacDevOpsYVR
• I love The Little Fish! – Command, Control, Power
• Ubiquiti Access, Protect, and more with Reilly Chase from HostiFi – Apple @ Work, 9to5Mac
• Journalism’s role in cybersecurity with Alfred Ng and Seth Rosenblatt – Lock and Code

Support

If you are enjoying what you are reading here, please spread the word and recommend it to another Mac Admin!

• Weblog
• Weekly Email Newsletter (TinyLetter)
• Apple News
• Twitter
• Micro.blog
• Mastodon.social
• Facebook
• LinkedIn

If you want to support me and this website even further, then consider buying one (or all) of my books. It’s like a subscription fee, but you also get a useful book or two extra!

• Moving to zsh
• macOS Installation for Apple Administrators
• Property Lists, Preferences and Profiles for Apple Administrators
• Packaging for Apple Administrators

For now this has been a quiet week. Since Apple announced another event next week, possibly a calm before the storm. After Apple announced iOS 14 with 24 hours notice, MacAdmins are understandably a bit nervous. Also, no new betas this week (so far).

On the other hand, after JNUC last week, we had MacSysAdmin this week. I have not been able to watch all presentations yet, but those that I have seen have been worth it and I am looking forward to the rest.

In other news, this newsletter just passed the 1000 email subscribers number! Thank you all for reading, and on to the next thousand!

If you would rather get the weekly newsletter by email, you can subscribe to the Scripting OS X Weekly Newsletter here!! (Same content, delivered to your Inbox once a week.)

News and Opinion

• Windows 10 machines running on ARM will be able to emulate x64 apps soon – Samuel Axon, Ars Technica
• Last Week on My Mac: Pretend it never happened – Howard Oakley
• MacSysAdmin 2020 – Ed Marczak

macOS 11 Big Sur and iOS 14

• Big Sur’s Hidden Document Proxy Icon – Michael Tsai

MacAdmins on Twitter

• Eliz: “Please don’t say just “Hello” in a chat #NoHello” (Read thread and links for background. I find myself doing that a lot, too, and have resvoled to do better.)

Bugs and Security

• We Hacked Apple for 3 Months: Here’s What We Found – Sam Curry

Support and HowTos

• How To Downgrade Safari 14 to 13 – Supported & Unsupported Options – Mr. Macintosh
• A sneaky peak at the new Jamf Self Service – Mod Titan
• MacSysAdmin 2020 update: This One Goes to 11 – Greg Neagle
• This One Goes to 11: macOS version comparisons and Munki – Greg Neagle
• VMware Fusion Player 12 is FREE! Test macOS, Linux or Windows 10 – Mr Macintosh
• Inside the file system: 3 APFS containers and volumes – Howard Oakley
• Managing and reporting unauthorized (admin) account creation – Frederick Abeloos

Scripting and Automation

• Environment Variables – Julia Evans
• Brackets Cheatsheet – Julia Evans
• Working with Swifty NSNotification – Alexis Bridoux

Updates and Releases

• Munki 5.1.1 Official Release
• Munki 5.2 Beta 1

To Watch

• MacSysAdmin Online 2020

To Listen

• Apple Pay? – Command Control Power
• Hey Siri, Save My Mom – MacDevOpsYVR

Support

If you are enjoying what you are reading here, please spread the word and recommend it to another Mac Admin!

• Weblog
• Weekly Email Newsletter (TinyLetter)
• Apple News
• Twitter
• Micro.blog
• Mastodon.social
• Facebook
• LinkedIn

If you want to support me and this website even further, then consider buying one (or all) of my books. It’s like a subscription fee, but you also get a useful book or two extra!

• Moving to zsh
• macOS Installation for Apple Administrators
• Property Lists, Preferences and Profiles for Apple Administrators
• Packaging for Apple Administrators