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.
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
Is bash gone!?
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
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
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/bash are 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),
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?
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 MacBook%
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
If you want to already switch your default shell to
zsh you can use the
$ chsh -s /bin/zsh
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?
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
zsh is configuration. Since
zsh ignores the
bash configuration files (
.bashrc) you cannot simply copy customized bash settings over to
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
I am planning a separate post, describing how to transfer (and translate) your configurations from
What about scripting?
zsh has been present on macOS for a long time, you could start moving your scripts from
zsh right away and not lose backwards compatibility. Just remember to set the shebang in your scripts to
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
Since we now know that
bash is eventually going away, the only common choice left is
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 fucntionality, but it seems like the safest choice for continued support.
Overall, while the messaging from Apple is very interesting, the change itself is less dramatic than the headlines. Apple is not ‘replacing’
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!
This git repo has been shared by many on MacAdmins Slack: rothgar/mastering-zsh, I will certainly dive into that and share about my experiences here!