Linux Hacks

518 Articles

Linux Fu: Curling C

February 15, 2024 by 11 Comments

Sometimes, it pays to read the man pages of commands you use often. There might be a gem hidden in there that you don’t know about. Case in point: I’ve used curl (technically, cURL, but I’m going to stick with curl) many times to grab data from some website or otherwise make a web request. But what happens if you want to do the same thing from a C program? Well, you could be lazy and just spawn a copy of curl. But it turns out curl has a trick up its sleeve that can help you. If only I’d read the man page sooner!

First Things

The simplest use of curl is to just name a URL on the command line. For example, consider this session:

$ curl http://www.hackaday.com 
<html>
<head><title>301 Moved Permanently</title></head>
<body>
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx</center>
</body>
</html>

This isn’t so useful because it is a 301 response (to send you to the https server, in this case). The -L option will make curl go get the page instead of the redirect. Try:

$ curl -L http://www.hackaday.com

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Linux Fu: Where’s That Darn File?

January 17, 2024 by 20 Comments

Disk storage has exploded in the last 40 years. These days, even a terabyte drive is considered small. There is one downside, though. The more stuff you have, the harder it is to find it. Linux provides numerous tools to find files when you can’t remember their name. Each has plusses and minuses, and choosing between them is often difficult.

Definitions

Different tools work differently to find files. There are several ways you might look for a file:

  1. Find a file if you know its name but not its location.
  2. Find a file when you know some part of its name.
  3. Find a file that contains something.
  4. Find a file with certain attributes (e.g., larger than 100 kB)

You might combine these, too. For example, it is reasonable to query all PDF files created in the last week that are larger than 100 kB.

There are plenty of different types of attributes. Some file systems support tags, too. So, you might have a PERSONAL tag to mark files that apply to you personally. Unfortunately, tool support for tags is somewhat lacking, as you’ll see later.

Another key point is how up-to-date your search results are. If you sift through terabytes of files for each search, that will be slow. If you keep an index, that’s fast, but the index will quickly be out of date. Do you periodically refresh the index? Do you watch the entire file system for changes and then update the index? Different tools do it differently. Continue reading “Linux Fu: Where’s That Darn File?” →

Linux Fu: Name That Tune

January 11, 2024 by 9 Comments

If you aren’t old enough to remember, the title of this post refers to an old game show where contestants would try to name a tune using the fewest possible notes. What can we say? Entertainment options were sparse before the Internet. However, using audio fingerprinting, computers are very good at pulling this off. The real problem is having a substantial library of fingerprints to compare with. You can probably already do this with your phone, and now you can do it with your Linux computer.

In all fairness, your computer isn’t doing the actual work. In fact, SongRec — the program in question — is just a client for Shazam, a service that can identify many songs. While this is mildly interesting if you use a Linux desktop, we could also see using the same technique with a Raspberry Pi to get some interesting projects. For example, imagine identifying a song playing and adjusting mood lighting to match. A robot that could display song information could be the hit of a nerdy party.

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Welcome To The Year Of The Diagonal Linux Desktop

December 31, 2023 by 73 Comments

Sometimes you come across one of those ideas that at first appear to have to be some kind of elaborate joke, but as you dig deeper into it, it begins to make a disturbing kind of sense. This is where the idea of diagonally-oriented displays comes to the fore. Although not a feature that is generally supported by operating systems, [xssfox] used the xrandr (x resize and rotate) function in the Xorg display server to find the perfect diagonal display orientation to reach a happy balance between the pros and cons of horizontal and vertical display orientations.

As displays have gone wide-and-wider over the past decades, some people rotate their displays 90 degrees to get more height instead, which is beneficial when reading documents, yet terrible when watching most video content, barring vertical videos, so you either need more than one display, keep rotating, or settle on an optimal intermediate compromise. Interestingly, this wasn’t found at a straight 45°, but instead at 22° of rotation for [xssfox]’s 21:9 ratio ‘ultra-wide’ display. The xrandr settings for other display ratios can be easily calculated using the provided formula and associated JS-based tool.

So what are the advantages here? You get to keep long line lengths in IDEs, while gaining more vertical pixels in some areas. As disadvantages it only works with Xorg at this time, it’s a terrible setup for people prone to vertigo, and it’s decidedly hostile towards top-of-display mounted webcams. Yet with others picking up on this new trend, Linux might just corner the diagonal desktop.

Gentoo Linux, Now A Bit Less For The 1337

December 29, 2023 by 37 Comments

Among users of Linux distributions there’s a curious one-upmanship, depending on how esoteric or hardcore  your distro is. Ubuntu users have little shame, while at the other end if you followed Linux From Scratch or better still hand-compiled the code and carved it onto the raw silicon with a tiny chisel, you’re at the top of the tree*. Jokes aside though, it’s fair to say that if you were running the Gentoo distribution you were something of a hardcore user, because its source-only nature meant that everything had to be compiled to your liking. We’re using the past tense here though, because in a surprise announcement, the distro has revealed that it will henceforth also be available as a set of precompiled binary packages.

There may be readers with long and flowing neckbeards who will decry this moment as the Beginning of the End, but while it does signal a major departure for the distro if it means that more people are spurred to take their Linux usage further and experiment with Gentoo, this can never be a bad thing. Gentoo has been on the list for a future Jenny’s Daily Drivers OS review piece, and while we’re probably going to stick with source-only when we do it, it’s undeniable that there will remain a temptation to simply download the binaries.

Meanwhile this has been written on a machine running Manjaro, or Arch-for-cowards as we like to call it, something that maybe confers middle-ranking bragging rights. Read a personal tale of taking off those Linux training wheels.

* Used a magnifying glass? You’re just not cutting it!

Linux Fu: Preprocessing Beyond Code

December 28, 2023 by 15 Comments

If you glanced at the title and thought, “I don’t care — I don’t write C code,” then hang on a minute. While it is true that C has a preprocessor and you can notoriously do strange and — depending on your point of view — horrible or wonderful things with it, there are actually other options and you don’t have to use any of them with a C program. You can actually use the C preprocessor with almost any kind of text file. And it’s not the only preprocessor you can abuse this way. For example, the m4 preprocessor is wildly complex, vastly underused, and can handle C source code or anything else you care to send to it.

Definitions

I’ll define a preprocessor as a program that transforms its input file into an output file, reacting to commands that are probably embedded in the file itself. Most often, that output is then sent to some other program to do the “real” work. That covers cpp, the C preprocessor. It also covers things like sed. Honestly, you can easily create custom preprocessors using C, awk, Python, Perl, or any other programming language. There are many other standard programs that you could think of as preprocessors, for example, tr. However, one of the most powerful is made to preprocess complex input files called m4. For some reason — maybe because of its complexity — you don’t see much m4 in the wild.

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Modern Control Of A Logic Analyzer

December 27, 2023 by 8 Comments

When you think of a logic analyzer today, you might think of a little USB probe that can measure a few signals and decoding for various serial buses. But actual logic analyzers were high-speed multichannel hardware with sophisticated ways to clock and trigger. [Tom] picked up an HP1670G on the surplus market and was impressed that it could sample 136 channels at 500 MHz. The circa-2000 machine has a front panel, but if you really wanted to use it, you wanted to use an X terminal. [Tom] shows us how that works with modern Linux software.

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