WTF is a “command” or “passing arguments”? Making Sense of the Command Line

Meow Meow.. Let’s understand how commands, “passing things” to them and “executing” or “running” them works in the terminal/shell by giving hard definitions for what we think we understand a term (pun intended) to mean and how the operating system, shell, scripts, apps, commands, functions and arguments work and how our mental model of them may be (very) skewed.

The following command will replace the prefix for screenshots you automatically capture or crop to your desktop in OS X to “SS” instead of the default “Screen Shot”, just to use as an example. If hit cmd+space type ‘term‘ and wait for ambiguities or hit Return. A terminal window or “shell” where you can type stuff hopefully opens. WTF just happened?

You hit a universal OS X shortcut that runs Mac’s built in open command to execute some binary file (meaning a compiled source file) somewhere in
Then pass its main function 1 parameter, a string argument with a value of “term”- it does a fuzzy or wildcard search in the index of every single file/directory on your machine (except those you exclude)
defaults write name “SS” && killall SystemUIServer


defaults.write(defaults.get('').name('Screen Shot')

Let’s define some terms first

Kernel is the OS itself. The set of “functions” people at Apple, people they contracted and people before them wrote you’re running on the very expensive hardware Apple sold you. The Kernel class is a blueprint or sketch on a napkin, or a form of Plato’s kind, not a tangible thing, except in the following code syntax context, where tangible means a thing you can make instance an of, copy, mutate, read, write-to, etc. A tangible class is an instantiated object, rather than being an abstract class. Thing of a chair class vs an actual chair. Your physical body cannot sit on an abstract chair. It must exist. The “abstract chair” itself cannot just transform to a wooden tangible chair that follows the same rules as your body. It is only an idea, an electrical pattern humans conditioned themselves to agree on so solidly that we can build/import/export/buy/sell/make-shift/DIY/fix and do a million other things with this concept of a chair.

A Tangible class means an object and an abstract object means a class. Kind of. Avoid these terms. They are only here as a koan to break you from your usual stream of consciousness.

`kill` is a function, procedure or method, a “verb” on the concrete object. You can and do have abstract functionality on abstract objects (aka classes),


function killall(name) {
   Kernel.kill(Kernel.findIdByProccess(name), SIGNAL_TERMINATE);

defaults is an app, probably written in a language called C or in another call =ed Objective-C and compiled. It could also be written in Ruby, Python, Java, Javascript, Lua, or another interpreted language (“script”) that has its “executable” permission set ON. If you see something like |rwx-rw-r defaults| It is simple in that it probably is written to serve a single purpose. The Unix philosophy is “Write something that does one thing and does it well.” “one thing” is relative. Is “email” one thing? Is browsing the web “one thing”? It used to be, but now browsers are extremely complex pieces of architecture that seemingly do different things for different user archtypes.


killall SystemUIServer

Hard restart of the SystemUIServer (just an app running in the background. You can also kill it the hard way without a terminal by killing it using killall after defaults succeeds (the && is important)
killall SystemUIServer


Terminal/iTerm2/console/shell/Bash/Zsh.. are these synonymous?