Broken Silence: Recounted Mac OS

Broken Silence: Recounted Mac Os 7
Broken Silence: Recounted Mac Os X

Apple has announced that in macOS 10.15 Catalina the default shell will be zsh.

In this series, I will document my experiences moving bash settings, configurations, and scripts over to zsh.

Part 1: Moving to zsh (this article)
Part 2: Configuration Files
Part 3: Shell Options
Part 4: Aliases and Functions
Part 5: Completions
Part 6: Customizing the zsh Prompt
Part 7: Miscellanea
Part 8: Scripting zsh

The code of silence between the mutually-contradictory creationist accounts is 'deafening.' I believe that the evolution of species and the theory of creation are on a level playing field. Of course it is, because the only 'theory of creation' we have so far is evolution. While we do have the Genesis account and evidence of.

Apple silicon: Turn on your Mac and continue to press and hold the power button until you see the startup options window. Click the gear icon labeled Options, then click Continue. Intel processor: Turn on your Mac, then immediately press and hold these two keys until you see an Apple logo or other image: Command (⌘) and R. Click the lock icon and enter your password. Hold the Ctrl key, click your user account’s name in the left pane, and select “Advanced Options.”. Click the “Login Shell” dropdown box and select “/bin/bash” to use Bash as your default shell or “/bin/zsh” to use Zsh as your default shell. Click “OK” to save your changes. Apple is strongly messaging that you should switch shells. This is different from the last switch in Mac OS X 10.3 Panther, when Apple switched the default to bash, but didn’t really care if you remained on tcsh. In fact, tcsh is still present on macOS. Apple’s messaging should tell us, that the days of /bin/bash are numbered.

zsh (I believe it is pronounced zee-shell, though zish is fun to say) will succeed bash as the default shell. bash has been the default shell since Mac OS X 10.3 Panther.

This series has grown into a book: reworked and expanded with more detail and topics. Like my other books, I plan to update and add to it after release as well, keeping it relevant and useful. You can order it on the Apple Books Store now.

Why?

The bash binary bundled with macOS has been stuck on version 3.2 for a long time now. bash v4 was released in 2009 and bash v5 in January 2019. The reason Apple has not switched to these newer versions is that they are licensed with GPL v3. bash v3 is still GPL v2.

zsh, on the other hand, has an ‘MIT-like’ license, which makes it much more palatable for Apple to include in the system by default. zsh has been available as on macOS for a long time. The zsh version on macOS 10.14 Mojave is fairly new (5.3). macOS 10.15 Catalina has the current zsh 5.7.1.

Is bash gone!?

No.

macOS Catalina still has the same /bin/bash (version 3.2.57) as Mojave and earlier macOS versions. This change is only for new accounts created on macOS Catalina. When you upgrade to Catalina, a user’s default shell will remain what it was before.

Many scripts in macOS, management systems, and Apple and third party installers rely on /bin/bash. If Apple just yanked this binary in macOS 10.15 Catalina or even 10.16. Many installers and other solutions would break and simply cease to function.

Users that have /bin/bash as their default shell on Catalina will see a prompt at the start of each Terminal session stating that zsh is now the recommended default shell. If you want to continue using /bin/bash, you can supress this message by setting an environment variable in your .bash_profile or .bashrc.

You can also download and install a newer version of bash yourself. Keep in mind that custom bash installations reside in a different directory, usually /usr/local/bin/bash.

Will bash remain indefinitely?

Apple is strongly messaging that you should switch shells. This is different from the last switch in Mac OS X 10.3 Panther, when Apple switched the default to bash, but didn’t really care if you remained on tcsh. In fact, tcsh is still present on macOS.

Apple’s messaging should tell us, that the days of /bin/bashare numbered. Probably not very soon, but eventually keeping a more than ten year old version of bash on the system will turn into a liability. The built-in bash had to be patched in 2014 to mitigate the ‘Shellshock’ vulnerability. At some point Apple will consider the cost of continued maintenance too high.

Another clue is that a new shell appeared on macOS Catalina (and is mentioned in the support article). The ‘Debian Almquist Shell’ dash has been added to the lineup of shells. dash is designed to be a minimal implementation of the Posix standard shell sh. So far, in macOS (including Catalina),sh invokes bash in sh-compatibility mode.

As Apple’s support article mentions, Catalina also adds a new mechanism for users and admins to change which shell handles sh invocations. MacAdmins or users can change the symbolic link stored in /var/select/sh to point to a shell other than /bin/bash. This changes which shell interprets scripts the #!/bin/sh shebang or scripts invoked with sh -c. Changing the interpreter for sh should not, but may change the behavior of several crucial scripts in the system, management tools, and in installers, but may be very useful for testing purposes.

All of these changes are indicators that Apple is preparing to remove /bin/bash at some, yet indeterminate, time in the future.

Do I need to wait for Catalina to switch to zsh?

No, zsh is available Mojave and on older macOS versions. You can start testing zsh or even switch your default shell already.

If you want to just see how zsh works, you can just open Terminal and type zsh:

The main change you will see is that the prompt looks different. zsh uses the % character as the default prompt. (You can change that, of course.) Most navigation keystrokes and other behaviors will remain the same as in bash.

If you want to already switch your default shell to zsh you can use the chsh command:

This will prompt for your password. This command will not change the current shell, but all new ones, so close the current Terminal windows and tabs and open a new one.

How is zsh different?

Like bash (‘Bourne again shell’ ), zshderives from the ‘Bourne’ family of shells. Because of this common ancestry, it behaves very similar in day-to-day use. The most obvious change will be the different prompt.

The main difference between bash and zsh is configuration. Since zsh ignores the bash configuration files (.bash_profile or .bashrc) you cannot simply copy customized bash settings over to zsh. zsh has much more options and points to change zsh configuration and behavior. There is an entire eco-system of configuration tools and themes called oh-my-zsh which is very popular.

zsh also offers better configuration for auto-completion which is far easier than in bash.

I am planning a separate post, describing how to transfer (and translate) your configurations from bash to zsh.

What about scripting?

Since zsh has been present on macOS for a long time, you could start moving your scripts from bash to zsh right away and not lose backwards compatibility. Just remember to set the shebang in your scripts to #!/bin/zsh.

You will gain some features where zsh is superior to bash v3, such as arrays and associative arrays (dictionaries).

There is one exception where I would now recommend to use /bin/sh for your scripts: the Recovery system does not contain the /bin/zsh shell, even on the Catalina beta. This could still change during the beta phase, or even later, but then you still have to consider older macOS installations where zsh is definitely not present in Recovery.

When you plan to use your scripts or pkgs with installation scripts in a Recovery (or NetInstall, or bootable USB drive) context, such as Twocanoes MDS, installr or bootstrappr, then you cannot rely on /bin/zsh.

Since we now know that bash is eventually going away, the only common choice left is /bin/sh.

When you build an installer package, it can be difficult to anticipate all the contexts in which it might be deployed. So, for installation pre- and postinstall scripts, I would recommend using /bin/sh as the shebang from now on.

I used to recommend using /bin/bash for everything MacAdmin related. /bin/sh is definitely a step down in functionality, but it seems like the safest choice for continued support.

Summary

Overall, while the messaging from Apple is very interesting, the change itself is less dramatic than the headlines. Apple is not ‘replacing’ bash with zsh, at least not yet. Overall, we will have to re-think and re-learn a few things, but there is also much to be gained by finally switching from a ten-year-old shell to a new modern one!

In the next part we will look at the configuration files for zsh.