Tag: bash

New Projects: jpt and shui, Now Available

brunerd

Between March and October 2020 I had some great ideas for command line Mac utilities the MacAdmin could apprecite and I had the time to devote to their realization. I’m excited to present these two open source projects, available on GitHub: jpt and shui. I hope they can add richness to your shell scripts’ presentation and capabilities without requiring additional external dependancies.

jpt – the “JSON Power Tool” is a Javascript and shell script polyglot that leverages jsc, the JavascriptCore binary that is standard on every Mac since 10.4 and since the jpt is purposefully written in ES5 to maintain maximum compatibility, why yes, this tool does run on both PPC and Intel Macs all the way back to OS X Tiger and then all the way forward to the latest 11.0 macOS Big Sur! Many Linux distros like CentOS and Ubuntu come with jsc pre-installed also, even Windows with the Linux Subsystem installed can run jsc and therefore can run the jpt!

What you can do with the jpt? Query JSON documents using either the simple yet expressive JSONPath syntax or the singular and precise JSON Pointer (RFC6901) syntax. The output mode is JSON but additional creative output modes can render JSONPaths, JSON Pointer paths, or even just the property names with their “constructor” types (try -KC with -J or -R) Textual output can be encoded in a variety of formats (hex/octal/URI encoding, Unicode code points, etc…), data can be modified using both JSON Patch (RFC6902) operations (add, replace, remove, copy, move, test) and also JSON Merge Patch (RFC7386) operations. JSON can be worked with in new ways, try -L for “JSONPath Object Literal” output to see what I mean. Or you simply feed jsc a file to pretty-print (stringify) to /dev/stdout. I’ll be writing more about this one for sure.
Github project page: jpt
Tagged blog posts: scripting/jpt

shui – first-class Applescript dialog boxes in your shell scripts without needing to remember esoteric Applescript phrasings! If you think it’s odd for code to have possessive nouns and are more comfortable in shell, you’re not alone. shui can be embedded in either bash or zsh scripts but it can also output Applescript if you really want to know how the sausage is made or want to embed in your script without shui. Hopefully shui will let you forget those awkward Applescript phrasing and focus on your shell script’s features and functionality. It uses osascript to execute the Applescript and launchctl to invoke osascript in the correct user context so user keyboard layouts are respected (vs. root runs). Check out the project page for demo videos and then give shui a try.
Project page: shui
Tagged blog posts: scripting/shui

macOS shell games: long live bash

brunerd

TL;DR – Bash ain’t goin’ nowhere on Mac, both version-wise and in terms of its presence. Looking at the longevity of other shells on the system, it will likely be around for a good while longer.

There’s been a lot of hand wringing and angst online about bash and zsh becoming the new default shell. Some folks feel Apple is signaling deprecation and removal and have the crushing feeling they must convert all their bash script to zsh. I think that’s a bit unnecessary.

True, the default shell is changing from bash to zsh, as Apple notes here. This is indeed a Good Thing™ as zsh shell has been one of the most frequently updated shells on macOS. Bash, on the other hand, has been stuck at varying versions of 3.2 for 12 years now! On the plus side, sysadmins have “enjoyed” predictable and stable behavior from bash during this time. Sure, you’d love new features but when you are scripting for the enterprise, across multiple OS versions, this is just the sort of thing you want: boringness and dependability.

As far as deprecations go, the only thing Apple has signaled as being deprecated eventually are scripting language runtimes (not shells):

Scripting language runtimes such as Python, Ruby, and Perl are included in macOS for compatibility with legacy software. Future versions of macOS won’t include scripting language runtimes by default, and might require you to install additional packages. If your software depends on scripting languages, it’s recommended that you bundle the runtime within the app. (49764202)

Use of Python 2.7 isn’t recommended as this version is included in macOS for compatibility with legacy software. Future versions of macOS won’t include Python 2.7. Instead, it’s recommended that you run python3 from within Terminal. (51097165)

mac OS Catalina 10.15 Release Notes

I’ve done some digging and culled the shell versions from OS X 10.0 to macOS 10.15, along with their respective release dates. I think it shows that shells, no matter how old and crusty, tend to be long lived and not soon removed on macOS.

Here’s a quick way to check your shell versions (except for dash):

macOSzshbash/shcsh/tcshkshdash
10.03.0.8 (2000-05-16)3.0.8 (zsh, no bash)6.08.00 (1998-10-02)––
10.13.0.8 (2000-05-16)3.0.8 (zsh, no bash)6.10.00 (2000-11-19)––
10.24.0.4 (2001-10-26)2.05b.0 (2002-07-17)6.10.00 (2000-11-19)––
10.34.1.1 (2003-06-19)2.05b.0 (2002-07-17)6.12.00 (2002-07-23)––
10.44.2.3 (2005-03-00)2.05b.0 (2002-07-17)6.12.00 (2002-07-23)M p (1993-12-28)–
10.54.3.4 (2007-04-19)3.2.17 (2007-05-01)6.14.00 (2005-03-23)M s+ (1993-12-28)–
10.64.3.4 (2008-11-03)3.2.48 (2008-11-18)6.15.00 (2007-03-03)M s+ (1993-12-28)–
10.74.3.11 (2010-12-20)3.2.48 (2008-11-18)6.17.00 (2009-07-10)M s+ (1993-12-28)–
10.84.3.11 (2010-12-20)3.2.48 (2008-11-18)6.17.00 (2009-07-10)JM 93u (2011-02-08)–
10.95.0.2 (2012-12-12)3.2.51 (2010-03-17)6.17.00 (2009-07-10)JM 93u (2011-02-08)–
10.105.0.5 (2014-01-06)3.2.57 (2014-11-07)6.17.00 (2009-07-10)AJM 93u+ (2012-08-01)–
10.115.0.8 (2015-05-31)3.2.57 (2014-11-07)6.18.01 (2012-02-14)AJM 93u+ (2012-08-01)–
10.125.2 (2015-12-02)3.2.57 (2014-11-07)6.18.01 (2012-02-14)AJM 93u+ (2012-08-01)–
10.135.3 (2016-12-12)3.2.57 (2014-11-07)6.18.01 (2012-02-14)AJM 93u+ (2012-08-01)–
10.145.3 (2016-12-12)3.2.57 (2014-11-07)6.18.01 (2012-02-14)AJM 93u+ (2012-08-01)–
10.155.7.1 (2019-02-03)3.2.57 (2014-11-07)6.21.00 (2019-05-08)AJM 93u+ (2012-08-01)dash-9 (1993)

As you can see, zsh has has been updated with almost every new release of macOS. Bash really hit a wall with 3.2 and as many have noted, it was v4’s change in licensing to GPLv3 that caused this (sh is really bash in sh compatibility mode so the versions are intertwined). csh/tcsh has the same duality thing going on and took a notably giant 7 year leap in 10.15 to a version from 2019. ksh has remained at the same version just as long as bash yet I don’t think anyone is fretting that ksh will be deprecated or removed. Finally, dash is just a weirdo that apparently disdains versioning! I used a combination of what /bin/dash and man dash to get some sort of crude answer.

So there you go: In my opinion, all signs point to bash being yet another shell on macOS for some time. Removing bash from macOS would break a lot of stuff and while that reason alone hasn’t stopped Apple before, I think they will let sleeping dogs lie. Go ahead and learn zsh, master it, customize it, or make it “sexy” but take the rumors of its demise on macOS with a grain of salt and dose of skepticism.

Determining the current console user in macOS

brunerd

There’s a few methods floating out on the web, but I’d just like to point out a quick and reliable way to get the current console user on macOS using stat. This works great with Fast User Switching and if the mac is at the login screen it will return root as the user

consoleUser=$(stat -f %Su /dev/console)

There you go! Now go forth and script.

Also, if you are using backticks ` to capture output (a.k.a. command substitution) then consider using the more modern and nest-able $(…) method, here’s a good reason why: Why is $(…) preferred over `…` (backticks)?

Nothing (bash style)

brunerd

The brunerd blog has been a whole lot of nothing lately, so let’s commemorate and celebrate with an entry featuring the premiere of the bash tag and category… hmm, which one is more useful? We’ll find out. Now as for nothing, there’s a legit command, special built-in to do nothing in bash!

man page for bash command :

: [arguments]

No effect; the command does nothing beyond expanding arguments and performing any specified redirections.  A zero exit code is returned.

 

Isn’t that lovely? When you need to do nothing, you can call :
Perhaps you are writing a script and aren’t sure what you’ll do for that if statement —

if [ "${this}" == "that" ]; then
#actually not sure what to do here, let's do nothing
:
else
echo "This else, I'll do"
fi

I made a gist here and I think I’ll keep making more. I’ll feature them here with the bash tag, if only as an auxillary backup of my brain and to add to the collective patchwork quilt of code we all use to get our ideas off the ground, when our reach is just a hare shy of grasp and we need a little help.

Also in the gist was a snippet of a novel use by kbeck at Extensis in his UTC removal script to use : to redirect a here document into itself and server as a comment block that doesn’t need # on every line to be treated as a comment —

: <<COMMENTBLOCK

[ ] 2016-0324: enclose me; love me. i am a block of comments

COMMENTBLOCK

Spiffy!