Blowing Up Shell Scripts

September 18, 2024 by Bryan Cockfield 24 Comments

One of the most universal experiences of any Linux or Unix user is working through a guide or handbook and coming across an almost unbelievably complex line of code meant to be executed with a shell. At the time of encountering a snippet like this it’s difficult to imagine any human ever having written it in the first place, but with some dedication it is possible to tease out what these small bits of code do when they’re typed into the terminal and run (unless it’s something like :(){ :|:& };: but that’s another story entirely). [noperator] recently built a tool which helps users in this predicament understand these shell scripts by expanding them into a more human-intelligible form.

The tool is named sol and does much more than expanding shell one-liners into a readable format. It also provides an interactive shell environment where the user can explore the exploded code in detail, modify it in any way they see fit, and collapse it back down to a single line so it can easily be sent to other users. It can be used with most of the major text editors as well as piped directly to standard input, and has a number of other options as well such as custom configurations and the ability to see non-standard bits of code that might not be compatible from one shell environment to another, as well as helping to translate those bits of code.

[noperator] has made the code available in the linked GitHub page for anyone curious about its use, and has a to-do list for future versions of the tool as well including adding support beyond bash. We’d definitely recommend a tool like this especially if you’re still relatively new to bash scripting (or shell scripting in general) and, as always, we’d just to remind everyone not to blindly copy and paste commands into their terminal windows. If you’re the type of person to go out on a limb and run crazy commands to see what they actually do, though, make sure you’re at least logged into the right computer first.

Archiving Data On Paper Using 2D Images

September 15, 2024 by Dave Rowntree 44 Comments

It seems like only yesterday we covered a project using QR codes to archive data on paper (OK, it was last Thursday), so here’s another way to do it, this time with a dedicated codec using the full page. Optar or OPTical ARchiver is a project capable of squeezing a whopping 200 Kb of data onto a single A4 sheet of paper, with writing and reading achieved with a standard laser printer and a scanner. It’s a bit harder than you might think to get that much data on the page, given that even a 600 DPI printer can’t reliably place every dot each time. Additionally, paper is rarely uniform at the microscopic scale, so Optar utilizes a forward error-correcting coding scheme to cater for a little irregularity in both printing and scanning.

The error-correcting scheme selected was an Extended Golay code (24, 12, 8), which, interestingly, was also used for image transmission by the NASA Voyager 1 and 2 missions. In information theory terms, this scheme has a minimum Hamming Distance of 8, giving detection of up to seven bit errors. This Golay code implementation is capable of correcting three-bit errors in each 24-bit block, with 12 bits available for payload. That’s what the numbers in those brackets mean.

Another interesting problem is paper stretch during printing. A laser printer works by feeding the paper around rollers, some of which are heated. As a printer wears or gets dirty, the friction coefficient along the rollers can vary, leading to twisting and stretching of the paper during the printing process. Water absorbed by the paper can also lead to distortion. To compensate for these effects, Optar regularly inserts calibration targets throughout the bit image, which are used to locally resynchronize the decoding process as the image is processed. This is roughly similar to how the alignment patterns work within larger QR codes. Finally, similar to the position detection targets (those square bits) in QR codes, Optar uses a two-pixel-wide border around the bit image. The border is used to align to the corners well enough to locate the rows of bits to be decoded.

In the distant past of last week, we covered a similar project that uses QR codes. This got us thinking about how QR codes work, and even if encoding capacity can be increased using more colors than just black and white?

Thanks to [Petr] for the tip!

Create Custom Gridfinity Boxes Using Images Of Tools

September 14, 2024 by Dave Rowntree 3 Comments

We love it when a community grabs hold of an idea and runs wild with it despite obvious practicality issues. Gridfinity by YouTuber [Zach Freedman] is one of those concepts. For the unaware, this is a simple storage system standard, defining boxes to hold your things. These boxes can be stacked and held in place in anything from a desk drawer to hanging off the side of a 3D printer. [Georgs Lazdāns] is one such Gridfinity user who wanted to create tool-specific holders without leaving the sofa. To do so, they made a web application using node.js and OpenCV to extract outlines for tools (or anything else) when photographed on a blank sheet of paper.

The OpenCV stack assumes that the object to be profiled will be placed on a uniformly colored paper with all parts of its outline visible. The first part of the stack uses a bilateral filter to denoise the image whilst keeping edge details.

Next, the image is converted to greyscale, blurred, and run through an adaptive threshold. This converts the image to monochrome, again preserving edge details. Finally, the Canny algorithm pulls out the paper contour. The object outline can be given an accurate scale with the paper contour and paper size specified. The second part of the process works similarly to extract the object outline. The second contour should follow the object pretty accurately. If it doesn’t, it can be manually tweaked in the editor. Once a contour is captured, it can be used to modify a blank Gridfinity base in the model editor.

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Back Up Your Data On Paper With Lots Of QR Codes

September 12, 2024 by Lewin Day 55 Comments

QR codes are used just about everywhere now, for checking into venues, ordering food, or just plain old advertising. But what about data storage? It’s hardly efficient, but if you want to store your files in a ridiculous paper format—there’s a way to do that, too!

QR-Backup was developed by [za3k], and is currently available as a command-line Linux tool only. It takes a file or files, and turns them into a “paper backup”—a black-and white PDF file full of QR codes that’s ready to print. That’s legitimately the whole deal—you run the code, generate the PDF, then print the file. That piece of paper is now your backup. Naturally, qr-backup works in reverse, too. You can use a scanner or webcam to recover your files from the printed page.

Currently, it achieves a storage density of 3KB/page, and [za3k] says backups of text in the single-digit megabyte range are “practical.” You can alternatively print smaller, denser codes for up to 130 KB/page.

Is it something you’ll ever likely need? No. Is it super neat and kind of funny? Yes, very much so.

We’ve seen some other neat uses for QR codes before, too—like this printer that turns digital menus into paper ones. If you’ve got your own nifty uses for these attractive squares, let us know!

OpenSCAD Library Creates QR Codes On The Fly

September 4, 2024 by Tom Nardi 18 Comments

If you’ve been reading Hackaday for awhile, you’ll know we’re big fans of OpenSCAD around these parts. There’s a number of reasons it’s a tool we often reach for, but certainly one of the most important ones is its parametric nature. Since you’re already describing the object you want to generate with code and variables, it’s easy to do things like generate an arbitrary number of cloned objects by using a for loop.

There are a number of fantastic OpenSCAD libraries that explore this blurred line between code and physical objects, and one that recently caught our eye is scadqr from [xypwn]. The description says it lets you “Effortlessly generate QR codes directly in OpenSCAD”, and after playing around with it for a bit, we have to agree.

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Online Game Becomes Unexpected PixelFlut

August 30, 2024 by Jenny List 3 Comments

Blink and you could have missed it, but a viral sensation for a few weeks this summer was One Million Checkboxes, a web page with as you might expect, a million checkboxes. The cool thing about it was that it was interactive, so if you checked a box on your web browser, everyone else seeing that box also saw it being checked. You could do pixel art with it, and have some fun. While maintaining it, its author [eieio] noticed something weird, a URL was appearing in the raw pixel data. Had he been hacked? Investigation revealed something rather more awesome.

The display of checkboxes was responsive rather than fixed-width, on purpose to stop people leaving objectionable content. Any pixel arrangement would only appear as you made it to someone viewing with exactly the same width of checkboxes. But still, the boxes represented a binary bitfield, so of course people saw it and had fun hacking. The URLs appeared because they were ASCII encoded in the binary, and were left on purpose as a message to the developer inviting him to a forum.

On it he found a disparate group of teen hackers who’d formed a community having fun turning the game into their own version of a Pixelflut. If you’ve not seen the game previously, imagine a screen on which all pixels are individually addressable over the internet. Place it in a hackerspace or in the bar at a hacker camp, and of course the coders present indulge in a bit of competitive pixel-spamming to create a colorful and anarchic collaborative artwork. In this case as well as artwork they’d encoded the forum link in several ways, and had grown a thriving underground community of younger hackers honing their craft. As [eieio] did, we think this is excellent, and if any of the checkbox pixelflutters are reading this, we salute you!

Before he eventually took the site down he removed the rate limit for a while to let them really go to town, and predictably, they never gave up on the opportunity, and didn’t let him down.

Some people would call the activity discussed here antisocial, but in particular we agree with the final point in the piece. Young hackers like this don’t need admonishment, they need encouragement, and he’s done exactly the right thing. If you want to read more about Pixelflut meanwhile, we’ve been there before.

Simulating Air Flow For 3D Printing

August 25, 2024 by Al Williams 1 Comment

You’ve probably heard that a 3D printer is capable of producing its own replacement parts. Sometimes, that even includes upgraded or improved versions of the parts it was originally built with. But sometimes, it’s hard to figure out what improved really means. Think about air ducts that cool the part after printing. In theory, it should be easy to design a new duct. But how does it perform? Empirical testing can be difficult, but [Mike] shows how you can simulate the airflow so you can test design changes and validate assumptions before you print the actual part.

Of course, this wouldn’t only apply to printer ducts. You might also get some tips if you want to model airflow for PC cooling, hot air soldering, or other air-related projects. The free version of the software has some limitations, but it was surprisingly capable.

We also enjoyed how [Mike] used fluid to visualize the actual patterns and compared it to the simulation. The trick is using a compound from a kid’s science project kit, and it seems to work very well. Of course, you could just grab your smartphone. This might be worth thinking about if you are building a laser cutter air assist, too.

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