WEBVTT 00:00:00.000 --> 00:00:03.600 Imagine you're dropped, completely blindfolded, 00:00:03.600 --> 00:00:06.660 into this massive, just infinitely expanding 00:00:06.660 --> 00:00:08.560 office building. Oh, that sounds terrifying. 00:00:08.679 --> 00:00:10.580 Right. I mean, you have absolutely no idea what 00:00:10.580 --> 00:00:13.480 floor you're on, what wing you're in, or which 00:00:13.480 --> 00:00:15.679 department even surrounds you. You're just totally 00:00:15.679 --> 00:00:18.120 lost. Exactly. So you take off the blindfold, 00:00:18.440 --> 00:00:21.059 but every single hallway looks exactly the same. 00:00:21.420 --> 00:00:24.239 Yeah, the classic maze. Yeah. And you need a 00:00:24.239 --> 00:00:27.280 way to figure out where you are before you can, 00:00:27.280 --> 00:00:29.719 you know, actually do any work at all. You need 00:00:29.719 --> 00:00:32.079 the digital equivalent of finding that giant, 00:00:32.079 --> 00:00:35.340 you are here, red dot on a mall map. Which is 00:00:35.340 --> 00:00:38.119 so crucial. Right. And for you, sitting right 00:00:38.119 --> 00:00:40.119 there at your computer today, that red dot is 00:00:40.119 --> 00:00:43.259 actually a seemingly simple string of just three 00:00:43.259 --> 00:00:47.159 lowercase letters. PWD. Right. Which stands for 00:00:47.159 --> 00:00:50.289 Print Working Directory. And welcome to today's 00:00:50.289 --> 00:00:52.429 dupe dive, by the way. Our mission today is to 00:00:52.429 --> 00:00:55.009 take this single Wikipedia article about a basic 00:00:55.009 --> 00:00:58.549 terminal command and we'll extract a really profound 00:00:58.549 --> 00:01:00.990 exploration of how we orient ourselves in digital 00:01:00.990 --> 00:01:04.689 spaces. It's such a great topic because those 00:01:04.689 --> 00:01:08.150 three keystrokes, they carry like the entire 00:01:08.150 --> 00:01:11.870 weight of user orientation and actually looking 00:01:11.870 --> 00:01:14.530 at the backdrop we have of today, this massive 00:01:14.530 --> 00:01:17.469 sprawling blueprint of a digital file system. 00:01:18.269 --> 00:01:20.769 You can really see why it's necessary. It's huge. 00:01:21.150 --> 00:01:22.909 Yeah. Because a digital file system isn't just 00:01:22.909 --> 00:01:26.390 a simple list. It is a labyrinth. Without establishing 00:01:26.390 --> 00:01:29.329 your current context, navigation is just impossible. 00:01:29.510 --> 00:01:32.329 You're flying blind. Exactly. You can't safely, 00:01:32.329 --> 00:01:35.390 you know, move a file or delete a document or 00:01:35.390 --> 00:01:38.150 even run a program if you don't possess absolute 00:01:38.150 --> 00:01:40.549 certainty about your current location of that 00:01:40.549 --> 00:01:42.909 architecture. Okay, let's unpack this. Because 00:01:42.909 --> 00:01:45.049 we use this command, or at least it's graphical 00:01:45.049 --> 00:01:47.209 equivalence, like folders on a desktop every 00:01:47.209 --> 00:01:49.150 single day, right? Usually without a second thought. 00:01:49.209 --> 00:01:50.930 Oh, totally. We just take it for granted. We 00:01:50.930 --> 00:01:54.030 do. But to understand why we still rely on this 00:01:54.030 --> 00:01:56.390 you are here dot today, we really have to look 00:01:56.390 --> 00:01:59.189 back at exactly when and why it was first drawn. 00:01:59.609 --> 00:02:01.329 Because solving the whole where am I problem 00:02:01.329 --> 00:02:03.549 is like one of the oldest challenges in computing. 00:02:03.650 --> 00:02:05.569 It really is. And the source material actually 00:02:05.569 --> 00:02:09.370 traces this specific solution back exactly 51 00:02:09.370 --> 00:02:14.939 years. So we're talking June 1974. Wow, 1974. 00:02:15.240 --> 00:02:17.080 Yeah. We're looking at the laboratories of AT 00:02:17.080 --> 00:02:19.919 &T Bell Labs. And the command actually inherited 00:02:19.919 --> 00:02:22.740 its DNA from an even older operating system called 00:02:22.740 --> 00:02:26.360 Multics. Oh, right. Multics. Yeah. In Multics, 00:02:26.520 --> 00:02:29.639 they utilized a longer command. It's called print 00:02:29.639 --> 00:02:32.819 underscore jubierre. Print underscore jubierre, 00:02:32.879 --> 00:02:34.689 which is just... I mean, that's a bit clunky 00:02:34.689 --> 00:02:36.969 to type out dozens of times a day. John, nobody 00:02:36.969 --> 00:02:38.949 wants to type that. Which is why, when it made 00:02:38.949 --> 00:02:41.469 the jump to version 5 Unix, it was streamlined 00:02:41.469 --> 00:02:44.949 down to just PWD. Three highly efficient letters. 00:02:45.189 --> 00:02:47.110 Much better. But if we connect this to the bigger 00:02:47.110 --> 00:02:49.389 picture. The pivotal moment in this command's 00:02:49.389 --> 00:02:51.349 history wasn't actually just its invention in 00:02:51.349 --> 00:02:53.990 1974. It was its standardization. Standardization. 00:02:54.110 --> 00:02:57.610 Yeah. By 1987, PWD was incorporated into the 00:02:57.610 --> 00:03:00.090 XOpen Portability Guide, and then it subsequently 00:03:00.090 --> 00:03:03.729 became a core part of PSX .1 and the single -unit 00:03:03.729 --> 00:03:05.610 specification. OK, wait. I have to pause you 00:03:05.610 --> 00:03:08.030 there because that feels like a massive overcomplication. 00:03:08.110 --> 00:03:10.669 How so? Well, if this command is literally just 00:03:10.669 --> 00:03:13.349 printing a location, like just spitting out the 00:03:13.349 --> 00:03:15.030 text of the folder you're currently sitting in, 00:03:15.659 --> 00:03:18.400 Why did it require an international official 00:03:18.400 --> 00:03:20.860 standard like the single -unit specification? 00:03:21.240 --> 00:03:24.620 I mean, isn't here just here? See, that's the 00:03:24.620 --> 00:03:27.439 trap. We take the concept of here completely 00:03:27.439 --> 00:03:30.539 for granted because, well, we experience physical 00:03:30.539 --> 00:03:32.740 space continuously. Right. I can look around. 00:03:32.860 --> 00:03:34.520 Exactly. You look around. You see the walls. 00:03:34.639 --> 00:03:36.919 You feel the chair you're sitting in. A computer 00:03:36.919 --> 00:03:39.840 doesn't possess innate spatial awareness. for 00:03:39.840 --> 00:03:43.819 a machine here is an incredibly complex abstraction 00:03:43.819 --> 00:03:45.979 to track. Oh, I see, because it's just data. 00:03:46.360 --> 00:03:49.580 Right. And when we discuss POSACACS, which is 00:03:49.580 --> 00:03:52.180 the Portable Operating System Interface, we have 00:03:52.180 --> 00:03:55.180 to remember the landscape of the 1980s. Computing 00:03:55.180 --> 00:03:57.900 back then was wildly fragmented. Like the Wild 00:03:57.900 --> 00:04:00.539 West. Total Wild West. You had dozens of different 00:04:00.539 --> 00:04:02.219 vendors building different machines, running 00:04:02.219 --> 00:04:04.699 different proprietary operating systems, handling 00:04:04.699 --> 00:04:07.099 file hierarchies in completely different ways. 00:04:07.340 --> 00:04:10.689 So if I wrote like, a script to automate some 00:04:10.689 --> 00:04:14.210 work, and I told it to save a file here, moving 00:04:14.210 --> 00:04:18.149 that script from an AT &T machine to, say, a 00:04:18.149 --> 00:04:20.470 Sun Microsystems machine might just cause the 00:04:20.470 --> 00:04:23.389 whole thing to crash. The script would be hopelessly 00:04:23.389 --> 00:04:26.290 lost. It wouldn't know what here meant on the 00:04:26.290 --> 00:04:30.250 new machine. So standardizing PWD via P06 wasn't 00:04:30.250 --> 00:04:33.009 just about handing the user a convenient flashlight. 00:04:33.050 --> 00:04:35.269 It was bigger than that. Yeah, it was about creating 00:04:35.269 --> 00:04:37.689 a universal foundational language for digital 00:04:37.689 --> 00:04:40.250 location. By including it in the single UNIX 00:04:40.250 --> 00:04:42.689 specification, the architects of modern computing 00:04:42.689 --> 00:04:44.850 were mandating that no matter who built the operating 00:04:44.850 --> 00:04:46.970 system, there had to be an identical mechanism 00:04:46.970 --> 00:04:50.470 to answer the question, where am I? Which naturally 00:04:50.470 --> 00:04:52.430 brings up the actual mechanics of that question, 00:04:52.649 --> 00:04:55.009 right? Because how a computer retrieves this 00:04:55.009 --> 00:04:57.829 information under the hood is fascinating. It 00:04:57.829 --> 00:04:59.769 means the machine has to somehow look at itself. 00:04:59.889 --> 00:05:01.769 It does. It has to investigate its own state. 00:05:01.870 --> 00:05:03.750 Right. And the architecture of location is where 00:05:03.750 --> 00:05:06.230 the engineering gets truly elegant. According 00:05:06.230 --> 00:05:08.370 to the sources, the standalone command is actually 00:05:08.370 --> 00:05:10.750 written in the C programming language. Yep, good 00:05:10.750 --> 00:05:14.029 ol' C. And the version bundled in the GNU core 00:05:14.029 --> 00:05:16.709 utilities, which is basically the backbone of 00:05:16.709 --> 00:05:19.610 countless modern systems, was authored by a developer 00:05:19.610 --> 00:05:22.350 named Jim Meiering. And under the hood, this 00:05:22.350 --> 00:05:25.910 C program relies heavily on POCX system functions, 00:05:26.529 --> 00:05:29.569 specifically one called GetCode. Right, which 00:05:29.569 --> 00:05:32.180 stands for Get Current Working Directory. Let's 00:05:32.180 --> 00:05:34.220 get into the gears of that, because when that 00:05:34.220 --> 00:05:37.300 C program calls GetCrewed, what is actually happening? 00:05:37.379 --> 00:05:39.519 If the computer doesn't have eyes to look around, 00:05:39.620 --> 00:05:42.339 how does it build the map? Well, it has to interrogate 00:05:42.339 --> 00:05:45.100 the operating system's churnal. And it does so 00:05:45.100 --> 00:05:47.699 by essentially walking backward. Walking backward. 00:05:47.779 --> 00:05:51.519 Yeah. So every file and folder on a Unix -like 00:05:51.519 --> 00:05:54.279 system has an underlying identifier called an 00:05:54.279 --> 00:05:57.839 inode, an index node. OK. When GetCrewed is triggered, 00:05:57.980 --> 00:05:59.800 the system looks at the inode of the directory 00:05:59.800 --> 00:06:02.230 you are currently sitting in. But the catch is, 00:06:02.529 --> 00:06:04.629 it doesn't know the full path yet. It only knows 00:06:04.629 --> 00:06:06.050 the number of the room it's currently standing 00:06:06.050 --> 00:06:08.550 in. So it has to, what, open the door and look 00:06:08.550 --> 00:06:10.410 down the hallway? Basically, yeah. It looks at 00:06:10.410 --> 00:06:12.250 the parent directory, which is represented by 00:06:12.250 --> 00:06:14.529 two dots, you know, dot dot in Unix. Right, the 00:06:14.529 --> 00:06:17.269 dot dot. It checks the parents in Ode, then it 00:06:17.269 --> 00:06:20.069 scans that parent's contents to find the name 00:06:20.069 --> 00:06:22.870 that matches the original rooms in Ode. Oh, wow. 00:06:23.129 --> 00:06:25.310 And once it finds the name, it steps into the 00:06:25.310 --> 00:06:28.009 parent. looks at the grandparent directory, finds 00:06:28.009 --> 00:06:30.610 the name matching the parent's inode, and repeats 00:06:30.610 --> 00:06:33.610 this entire process. It literally climbs up the 00:06:33.610 --> 00:06:37.410 directory tree. Piece by piece, translating abstract 00:06:37.410 --> 00:06:40.290 inode numbers into human -readable text strings 00:06:40.290 --> 00:06:42.730 until it finally hits the root of the entire 00:06:42.730 --> 00:06:45.209 drive. That's incredible. It's piecing together 00:06:45.209 --> 00:06:47.670 the breadcrumbs in reverse. It starts where I 00:06:47.670 --> 00:06:50.209 am and just asks every single folder above me, 00:06:50.410 --> 00:06:52.430 who are you and how do I relate to you, until 00:06:52.430 --> 00:06:54.990 it reaches the absolute top. That's exactly how 00:06:54.990 --> 00:06:58.180 it works. But wait! If it has to do that recursive 00:06:58.180 --> 00:07:01.240 climb like querying the kernel and reading disk 00:07:01.240 --> 00:07:03.519 in nodes every single time I ask where I am, 00:07:03.740 --> 00:07:06.560 isn't that incredibly slow? It's very computationally 00:07:06.560 --> 00:07:09.000 expensive, yes. I mean, if I'm navigating through 00:07:09.000 --> 00:07:11.500 20 nested folders, I don't want my computer doing 00:07:11.500 --> 00:07:13.879 a massive reverse search just to print my location, 00:07:13.879 --> 00:07:17.199 you know? And that exact realization leads to 00:07:17.199 --> 00:07:19.639 a crucial divergence in how podode is actually 00:07:19.639 --> 00:07:22.240 implemented on your machine today. While that 00:07:22.240 --> 00:07:26.189 standalone GNUC program exists, The PIDOE you 00:07:26.189 --> 00:07:28.709 use in everyday navigation is almost certainly 00:07:28.709 --> 00:07:31.129 not that program. Right. The source has mentioned 00:07:31.129 --> 00:07:33.970 this explicitly. It's a shell built in for modern 00:07:33.970 --> 00:07:38.810 Unix shells, like sh, ash, bash, ksh, and zh. 00:07:38.990 --> 00:07:41.389 Which is a vital architectural distinction. The 00:07:41.389 --> 00:07:44.569 actual command line interface you're typing into 00:07:44.569 --> 00:07:46.889 doesn't want to spawn a whole external process 00:07:46.889 --> 00:07:49.029 just to find out where it is. Let me try a mechanical 00:07:49.029 --> 00:07:51.509 analogy here to see if I've got this. OK. Calling 00:07:51.509 --> 00:07:55.129 the external standalone C program is like, If 00:07:55.129 --> 00:07:57.089 someone asks me where I am and I've completely 00:07:57.089 --> 00:07:59.529 lost my memory, I'd have to pull out my smartphone, 00:07:59.889 --> 00:08:02.470 open a GPS app, wait for it to ping the satellites, 00:08:02.670 --> 00:08:04.610 and read the coordinates back to you. Had to 00:08:04.610 --> 00:08:06.529 use an external tool to figure out my own location. 00:08:06.649 --> 00:08:08.649 Right, that's calling the C program. But a shell 00:08:08.649 --> 00:08:11.149 built in is like simply knowing my home address 00:08:11.149 --> 00:08:13.949 by heart. The shell program itself just perpetually 00:08:13.949 --> 00:08:16.209 knows where it is. That is a perfect analogy. 00:08:16.350 --> 00:08:18.610 Right. And the way it knows it by heart is by 00:08:18.610 --> 00:08:21.339 maintaining its own internal ledger. The shell 00:08:21.339 --> 00:08:24.759 relies on environment variables. Like PWD. Exactly. 00:08:25.319 --> 00:08:28.540 POSIX compliant shells set and constantly update 00:08:28.540 --> 00:08:30.639 two key variables whenever you navigate using 00:08:30.639 --> 00:08:34.230 the CD or change directory command. Gotcha. So 00:08:34.230 --> 00:08:37.929 there's the PWD variable, which caches the absolute 00:08:37.929 --> 00:08:40.529 path of your current working directory. And then 00:08:40.529 --> 00:08:43.269 there's old EPWD, which caches your previous 00:08:43.269 --> 00:08:45.570 working directory. Oh, so the shell is basically 00:08:45.570 --> 00:08:47.950 acting as its own cartographer. Every time I 00:08:47.950 --> 00:08:50.269 type a command to move to a new folder, before 00:08:50.269 --> 00:08:52.450 it even moves me, it crosses out the old address 00:08:52.450 --> 00:08:54.629 in its ledger and writes down the new one. Exactly. 00:08:54.730 --> 00:08:57.750 It updates old EPWD, writes the new location 00:08:57.750 --> 00:09:01.279 to PWD, and only then executes the move. It creates 00:09:01.279 --> 00:09:03.500 a perfectly seamless experience. So when I type 00:09:03.500 --> 00:09:06.799 PWD, the shell just intercepts it. Yep. It doesn't 00:09:06.799 --> 00:09:09.259 run Jim Meiering C program. It doesn't trigger 00:09:09.259 --> 00:09:11.759 the kernel to walk the NO tree. It just reads 00:09:11.759 --> 00:09:13.580 the text string it already has stored in the 00:09:13.580 --> 00:09:16.820 PWD variable and prints it to your screen. Instantaneous. 00:09:17.200 --> 00:09:19.919 Zero overhead. OK. Here's where it gets really 00:09:19.919 --> 00:09:22.970 interesting. Because relying entirely on this 00:09:22.970 --> 00:09:25.669 internal diary creates a massive blind spot, 00:09:25.830 --> 00:09:28.110 doesn't it? Oh, absolutely. If the shell is just 00:09:28.110 --> 00:09:30.309 trusting a text variable in its memory to tell 00:09:30.309 --> 00:09:32.950 me where I am, what happens when that memory 00:09:32.950 --> 00:09:34.769 conflicts with the physical architecture of the 00:09:34.769 --> 00:09:37.279 hard drive? Well, you've just isolated the tension 00:09:37.279 --> 00:09:40.340 between logical paths and physical paths. This 00:09:40.340 --> 00:09:43.159 is where the concept of location becomes highly 00:09:43.159 --> 00:09:45.679 philosophical. The sources highlight this tension 00:09:45.679 --> 00:09:48.899 using symbolic links. And a symbolic link, or 00:09:48.899 --> 00:09:51.460 a symlink, basically operates like a redirect. 00:09:51.740 --> 00:09:53.480 Right. The article gives a very clear example. 00:09:54.240 --> 00:09:56.259 Let's say you navigate into a directory called 00:09:56.259 --> 00:09:59.559 slash home slash symlinked. But structurally, 00:09:59.799 --> 00:10:02.350 on the actual spinning disk, That folder doesn't 00:10:02.350 --> 00:10:05.230 contain any data. It's merely a pointer, redirecting 00:10:05.230 --> 00:10:07.169 the system to a completely different physical 00:10:07.169 --> 00:10:10.049 location, like slash home slash Realtor. So the 00:10:10.049 --> 00:10:12.269 shellager says you walked into semlinked. Oh. 00:10:12.370 --> 00:10:14.590 But the actual read -write head of the hard drive 00:10:14.590 --> 00:10:17.690 is pulling data from Realtor. Exactly. And according 00:10:17.690 --> 00:10:20.850 to PSEX standards, the default behavior of PDODE 00:10:20.850 --> 00:10:22.929 is to display the directory with the symbolic 00:10:22.929 --> 00:10:26.289 link info intact. Yes, the logical path. Right. 00:10:26.330 --> 00:10:28.590 It acts as if you passed it the dash L switch. 00:10:28.960 --> 00:10:32.360 L for logical. So it explicitly tells you that 00:10:32.360 --> 00:10:36.360 you are in slash home slash symlinked. It affirms 00:10:36.360 --> 00:10:38.940 the shortcut. And if you want the physical truth, 00:10:39.320 --> 00:10:41.779 you have to force its hand by giving it the dash 00:10:41.779 --> 00:10:45.980 P switch. P for physical, that bypasses the symbolic 00:10:45.980 --> 00:10:49.259 link, queries the actual disk, and reveals you're 00:10:49.259 --> 00:10:52.779 physically sitting in slash home slash realtor. 00:10:52.899 --> 00:10:55.539 Which forces the system to drop the ledger, call 00:10:55.539 --> 00:10:57.720 the kernel, and actually walk that inno tree 00:10:57.720 --> 00:10:59.960 we talked about to find the raw geography of 00:10:59.960 --> 00:11:02.279 the hardware. Wait. Think about what that means. 00:11:02.340 --> 00:11:05.559 By defaulting to dash L, POCX requires the computer 00:11:05.559 --> 00:11:07.980 to essentially lie to me. Well, lie is a strong 00:11:07.980 --> 00:11:10.940 word, but yes. It mandates that the system maintain 00:11:10.940 --> 00:11:13.190 an illusion. Let's ground this in the real world. 00:11:13.350 --> 00:11:15.210 Think of a massive corporate headquarters. Yeah, 00:11:15.330 --> 00:11:17.629 I'm picturing it. I walk into the lobby, look 00:11:17.629 --> 00:11:19.250 at the directory on the wall, and it says the 00:11:19.250 --> 00:11:21.809 prestigious executive suite is in room 100. That's 00:11:21.809 --> 00:11:24.750 the logical dash L path. So I walk through the 00:11:24.750 --> 00:11:27.590 door labeled 100, feeling very important. But 00:11:27.590 --> 00:11:29.649 behind the scenes, the architectural blueprints 00:11:29.649 --> 00:11:32.250 of the building, the physical dash P path show 00:11:32.250 --> 00:11:34.809 that room 100 is actually just an annex built 00:11:34.809 --> 00:11:37.269 over the loading dock across town. That's a great 00:11:37.269 --> 00:11:40.289 way to look at it. By default, PWD looks at the 00:11:40.289 --> 00:11:42.629 lobby directory and tells me I'm in the executive 00:11:42.629 --> 00:11:45.149 suite. It intentionally hides the blueprints 00:11:45.149 --> 00:11:47.750 from me. What's fascinating here is that this 00:11:47.750 --> 00:11:50.389 choice reveals a core philosophy in computing. 00:11:51.100 --> 00:11:55.299 user convenience and mental continuity must supersede 00:11:55.299 --> 00:11:58.519 system reality. That's wild! The default dash 00:11:58.519 --> 00:12:01.899 L behavior prioritizes the human being's fragile 00:12:01.899 --> 00:12:04.559 mental map over the machine's absolute physical 00:12:04.559 --> 00:12:06.860 state. But why is the truth considered fragile? 00:12:07.000 --> 00:12:08.820 I mean, if the computer knows I'm actually in 00:12:08.820 --> 00:12:11.360 real day, why not just tell me? Consider the 00:12:11.360 --> 00:12:14.039 cognitive load on the user. You deliberately 00:12:14.039 --> 00:12:17.039 typed a command to enter a folder named simlinked. 00:12:17.230 --> 00:12:19.649 In your mind, you've opened that specific drawer 00:12:19.649 --> 00:12:21.990 in your filing cabinet. Right. I expect to be 00:12:21.990 --> 00:12:25.230 in SimLinked. If you immediately typed PWD to 00:12:25.230 --> 00:12:28.169 confirm your location and the computer scat out 00:12:28.169 --> 00:12:31.590 a completely different path, real D, a path you 00:12:31.590 --> 00:12:34.649 never explicitly typed or requested, what's your 00:12:34.649 --> 00:12:37.649 immediate reaction? Panic. I'd assume the system 00:12:37.649 --> 00:12:39.950 had been compromised or I'd made a catastrophic 00:12:39.950 --> 00:12:41.889 typo. I'd be like, how did I get here? What did 00:12:41.889 --> 00:12:45.610 I break? Exactly. The system maintains the logical 00:12:45.610 --> 00:12:48.190 illusion because the logical path is the only 00:12:48.190 --> 00:12:50.769 thing that matters to your workflow. It protects 00:12:50.769 --> 00:12:53.049 you from the underlying chaos of the machine. 00:12:53.269 --> 00:12:55.169 It's saying, yes, your command worked perfectly. 00:12:55.289 --> 00:12:57.250 You are exactly where you're meant to go, even 00:12:57.250 --> 00:12:59.750 if the data is physically fragmented across multiple 00:12:59.750 --> 00:13:02.970 drives elsewhere. Right. However, the engineers 00:13:02.970 --> 00:13:05.350 knew they couldn't permanently obscure the truth. 00:13:05.809 --> 00:13:08.429 They built in that dash P switch for administrators, 00:13:08.750 --> 00:13:11.029 for troubleshooting, and for complex scripting. 00:13:11.190 --> 00:13:13.529 Because sometimes you need reality. Exactly. 00:13:14.269 --> 00:13:17.049 When a script needs to calculate exact disk usage, 00:13:17.549 --> 00:13:20.039 it can't rely on illusions. It needs the cold 00:13:20.039 --> 00:13:22.320 physical reality of the hard drive. So the dash 00:13:22.320 --> 00:13:25.019 L flag is the map you draw for a tourist and 00:13:25.019 --> 00:13:27.600 the dash P flag is the map you give to the structural 00:13:27.600 --> 00:13:31.019 engineer. That's brilliant. Yes. And because 00:13:31.019 --> 00:13:33.980 this need to manage the user's mental map, this 00:13:33.980 --> 00:13:36.259 absolute necessity of establishing a baseline, 00:13:36.740 --> 00:13:39.840 where am I, is so deeply ingrained in how humans 00:13:39.840 --> 00:13:42.240 interact with machines, it makes perfect sense 00:13:42.240 --> 00:13:44.620 that the concept couldn't remain confined strictly 00:13:44.620 --> 00:13:47.639 to Unix. No, it had to spread. The anxiety of 00:13:47.639 --> 00:13:50.740 being lost isn't just an AT &T Bell Labs problem, 00:13:50.820 --> 00:13:53.460 it is a fundamental computing problem. Which 00:13:53.460 --> 00:13:56.100 totally explains why the source material documents, 00:13:56.299 --> 00:13:59.980 PWD, escaping its original ecosystem to... an 00:13:59.980 --> 00:14:02.600 incredible array of diverse platforms. Yeah, 00:14:02.700 --> 00:14:04.960 the section detailing its presence across other 00:14:04.960 --> 00:14:07.639 operating systems is a fascinating historical 00:14:07.639 --> 00:14:10.799 cross -section. It lists the command in incredibly 00:14:10.799 --> 00:14:13.379 obscure environments. Oh yeah, like Spardados 00:14:13.379 --> 00:14:16.259 X. Yes, an operating system for 8 -bit Atari 00:14:16.259 --> 00:14:19.960 computers, Panos, Calibrios, even Windows CE 00:14:19.960 --> 00:14:22.519 5 .0, the software that ran on those early chunky 00:14:22.519 --> 00:14:25.480 enterprise PDAs and mobile barcode scanners. 00:14:25.559 --> 00:14:28.220 Its command line included PW. The syntax might 00:14:28.220 --> 00:14:30.179 fluctuate across these, but the function remains 00:14:30.179 --> 00:14:33.000 really rigid. Even in Microsoft's modern PowerShell 00:14:33.000 --> 00:14:36.120 environment, PW isn't a standalone tool, but 00:14:36.120 --> 00:14:38.559 it's implemented as a standard alias for their 00:14:38.559 --> 00:14:41.600 own C tool called Get Location. And in older 00:14:41.600 --> 00:14:44.259 Microsoft environments, like command .com and 00:14:44.259 --> 00:14:46.700 the Windows command prompt, the equivalent is 00:14:46.700 --> 00:14:49.779 typing CD with no arguments. Instead of changing 00:14:49.779 --> 00:14:52.179 the directory, it just prints your current location. 00:14:52.340 --> 00:14:55.440 And OpenVMS, which is an entirely different lineage 00:14:55.440 --> 00:14:58.330 of operating systems, uses the phrase Show default. 00:14:58.509 --> 00:15:01.830 Show default context. It's a very precise way 00:15:01.830 --> 00:15:04.570 to articulate what we're actually asking the 00:15:04.570 --> 00:15:07.110 machine to do. It really is. But you know, the 00:15:07.110 --> 00:15:08.750 implementation that really caught my attention 00:15:08.750 --> 00:15:10.950 wasn't in an operating system at all. It was 00:15:10.950 --> 00:15:13.009 in numerical computing environments. Oh, like 00:15:13.009 --> 00:15:16.350 MATLAB. Yeah. Software used by scientists, researchers, 00:15:16.450 --> 00:15:19.909 and engineers for heavy data -intensive mathematics. 00:15:20.610 --> 00:15:23.809 Both MATLAB and GANU Octave include a P2D function 00:15:23.809 --> 00:15:26.710 with nearly identical functionality to the 1974 00:15:26.710 --> 00:15:28.929 original. Because when a researcher is executing 00:15:28.929 --> 00:15:32.649 complex matrix algebra or like analyzing gigabytes 00:15:32.649 --> 00:15:35.509 of fluid dynamics data, the underlying operating 00:15:35.509 --> 00:15:37.710 system fades into the background. The application 00:15:37.710 --> 00:15:40.370 itself becomes the universe. Precisely. So what 00:15:40.370 --> 00:15:42.590 does this all mean? I mean, if I'm running a 00:15:42.590 --> 00:15:45.289 massive simulation in MATLAB and I execute a 00:15:45.289 --> 00:15:47.590 script to save the output graphs, I still need 00:15:47.590 --> 00:15:50.090 to know exactly which folder those files are 00:15:50.090 --> 00:15:52.009 going to drop into. I need an anchor point. You 00:15:52.009 --> 00:15:54.269 have to have an anchor. It just marvels me that 00:15:54.269 --> 00:15:57.139 a tiny three -letter concept born out of Multics 00:15:57.139 --> 00:15:59.879 half a century ago has infiltrated everything 00:15:59.879 --> 00:16:04.399 from 8 -bit Ataris to raw math software to modern 00:16:04.399 --> 00:16:07.059 enterprise servers running PowerShell. It's everywhere. 00:16:07.279 --> 00:16:10.240 Whether you type P or UD or get location or show 00:16:10.240 --> 00:16:12.940 default, you're participating in a universal 00:16:12.940 --> 00:16:15.440 human ritual of seeking spatial confirmation. 00:16:16.039 --> 00:16:18.340 And seeing this exact functionality replicated 00:16:18.340 --> 00:16:21.960 across wildly different paradigms proves that 00:16:21.960 --> 00:16:24.860 establishing a baseline of current state is the 00:16:24.860 --> 00:16:27.080 absolute prerequisite for computation. You can't 00:16:27.080 --> 00:16:29.100 do anything without it. Right. You cannot manipulate 00:16:29.100 --> 00:16:31.220 data, you cannot calculate formulas, and you 00:16:31.220 --> 00:16:33.840 cannot execute code if you do not first establish 00:16:33.840 --> 00:16:36.129 your anchor point in the digital sea. The underlying 00:16:36.129 --> 00:16:38.649 hardware has evolved from room -sized mainframes 00:16:38.649 --> 00:16:41.450 reading magnetic tape to microscopic solid -state 00:16:41.450 --> 00:16:45.370 drives. But the human need for a simple textual 00:16:45.370 --> 00:16:48.870 confirmation of, you are here, hasn't shifted 00:16:48.870 --> 00:16:52.259 one inch. We have covered immense ground today, 00:16:52.259 --> 00:16:54.899 exploring a single terminal command. We traced 00:16:54.899 --> 00:16:58.360 its origins from the 1974 laboratories of Multics 00:16:58.360 --> 00:17:01.100 and version 5 Unix. A long journey. Definitely. 00:17:01.559 --> 00:17:04.519 And we examined the massive effort to standardize 00:17:04.519 --> 00:17:07.200 digital location through POSAX, ending that whole 00:17:07.200 --> 00:17:10.079 fragmentation of the 1980s. We opened up the 00:17:10.079 --> 00:17:12.559 C code to watch GetForward exhaustively walk 00:17:12.559 --> 00:17:15.619 the InnoTree and contrasted that with the elegant 00:17:15.619 --> 00:17:17.900 efficiency of modern shell built -ins keeping 00:17:17.900 --> 00:17:21.099 an internal diary with the PWD variable. And 00:17:21.099 --> 00:17:23.440 we dug into the deep philosophical tension between 00:17:23.440 --> 00:17:25.640 the dash L logical illusion that comforts the 00:17:25.640 --> 00:17:28.440 user's mental map and the dash P physical reality 00:17:28.440 --> 00:17:30.680 of the actual disk structure. So for you, the 00:17:30.680 --> 00:17:32.559 listener, the next time you open a folder on 00:17:32.559 --> 00:17:34.140 your computer, whether you're clicking a graphical 00:17:34.140 --> 00:17:36.799 icon on a Mac, navigating a PC file explorer 00:17:36.799 --> 00:17:39.660 or SSShing into a remote Linux server, remember 00:17:39.660 --> 00:17:42.519 that there is a 51 year lineage quietly working 00:17:42.519 --> 00:17:45.849 behind the glass. Always watching. Yeah. It is 00:17:45.849 --> 00:17:48.670 constantly updating variables, tracking your 00:17:48.670 --> 00:17:51.589 every mood, actively managing illusion so you 00:17:51.589 --> 00:17:53.930 never have to feel the anxiety of being lost 00:17:53.930 --> 00:17:56.950 in an infinitely expanding digital office building. 00:17:57.549 --> 00:18:00.109 It is your primary flashlight in the dark. Before 00:18:00.109 --> 00:18:02.109 we close out this deep dive, though, there's 00:18:02.109 --> 00:18:04.329 one final detail from the source material that 00:18:04.329 --> 00:18:06.990 demands attention. Oh, what's that? Tucked away 00:18:06.990 --> 00:18:09.230 at the bottom of the page, in the see also section, 00:18:09.529 --> 00:18:12.289 there's a link to the concept of a breadcrumb 00:18:12.289 --> 00:18:15.869 navigation trail. Oh, a breadcrumb trail. Navigational 00:18:15.869 --> 00:18:17.809 markers left behind like the old fairy tale. 00:18:18.230 --> 00:18:21.849 Exactly. See, PDUDD provides an absolute definitive 00:18:21.849 --> 00:18:24.809 statement of where you are right in this exact 00:18:24.809 --> 00:18:26.990 millisecond. It's a static dot on the map. Right. 00:18:27.029 --> 00:18:30.069 You are here. But a breadcrumb trail, which has 00:18:30.069 --> 00:18:32.589 become the standard in modern graphical file 00:18:32.589 --> 00:18:34.990 explorers and web design, tells you the story 00:18:34.990 --> 00:18:37.799 of how you got there. It displays the entire 00:18:37.799 --> 00:18:40.119 hierarchical sequence of folders you click through 00:18:40.119 --> 00:18:42.759 to arrive at your current destination. I see. 00:18:43.019 --> 00:18:45.420 So PUD is the destination. The breadcrumb is 00:18:45.420 --> 00:18:47.759 the journey. Which leaves us with a really compelling 00:18:47.759 --> 00:18:50.319 question about the future of user interfaces. 00:18:51.640 --> 00:18:54.359 As our digital environments grow infinitely more 00:18:54.359 --> 00:18:57.420 complex, incorporating decentralized cloud storage, 00:18:57.759 --> 00:19:00.380 virtual drives, and collaborative workspaces, 00:19:00.619 --> 00:19:03.279 we're simply knowing where we are in the moment. 00:19:03.529 --> 00:19:05.930 continue to be enough. That's a good point. Or 00:19:05.930 --> 00:19:07.930 will the sheer scale of the labyrinth require 00:19:07.930 --> 00:19:10.369 us to always remember the precise trail of exactly 00:19:10.369 --> 00:19:13.089 how we arrived? Is the destination enough, or 00:19:13.089 --> 00:19:15.289 is the story of the journey now required to keep 00:19:15.289 --> 00:19:18.049 us grounded? We will let you, the listener, mull 00:19:18.049 --> 00:19:20.049 over that the next time you find yourself deep 00:19:20.049 --> 00:19:23.170 down a rabbit hole of nested folders. Thank you 00:19:23.170 --> 00:19:25.670 for joining us on this deep dive into the architecture 00:19:25.670 --> 00:19:28.670 of location. Stay curious, keep exploring, and 00:19:28.670 --> 00:19:30.549 we will catch you on the next deep dive.