"This is not a real HTTP client."<p>It's a TCP client<p>curl is an HTTP client<p>I prefer TCP clients to HTTP clients. Simpler, easier to modify, faster to compile<p>There are many to choose from. For example, I use a modified version of tcploop<p>For generating HTTP, I use own utilties. This is more flexible than curl. There are some things curl cannot do, even though it has too many options
As a kid in the late 90s my mind was blown when I realized I could telnet to port 80, 25, or 110 and interact with the servers manually.<p>Simple get:
GET / HTTP/1.1
Content-Type: text/html
User-Agent: l33t hax0rs lol
X-Funny-Monkey: farts<p>For sending a mail message on port 25:
HELO
mail-from: whoever@whatever.com
mail-to: sysadmin@yaya.com
<other headers>
<blank line>
Body of the message yay.
<two blank lines to end><p>POP3 was so long ago I forgot but you could list the mailboxes then get individual messages and so on.<p>This revelation was the beginning of "there is no magic" for me. The realization that every part of the computer was built by human beings and was at some level understandable if one undertook the effort.<p>Perhaps most people in the future won't bother. They'll just let agents do it all. I'm sure that will leave some interesting holes in various systems for people willing to actually learn how they work without the filter of a model (or its safety rails).
I sent many an email from jacques.chirac@elysee.fr, the veneer of the terminal helping, my friends were quite impressed by how good a hacker I was. Good olde days when many DKIM/SPF weren't a thing yet and SMTP servers weren't even authenticated.
"Cher compatriote, voici, rédigé avec mes clavier et mulot, mon programme de l'an 2000 que j'ai après la dissolution..."
Back in those days not only was there was no DKIM or SPF, most SMTP servers would accept email from anyone anywhere to anyone anywhere (i.e. 'open relay').
[ Note: Anyone who has been a geek since the 90s, there's nothing you don't already know here ]<p>> most SMTP servers would accept email from anyone anywhere to anyone anywhere (i.e. 'open relay').<p>to date that claim, I'd say that by the late 90s at least, true open relays ("from anyone to anyone") were still numerous but carried a huge assumption of being part of spam operations (willingly or through ineptitude), and the most basic spam filtering would reject mail that came out of one.<p>That said, (before things like SPF) it was easy enough to deliver email to anyone you wanted even if you didn't have your own real email account and SMTP server; you could just look up the destination's MX and connect to it with telnet like that. Since your own random IP probably wasn't blocklisted it would generally be accepted and delivered.<p>Back then it was still basically considered bad form to reject email simply because the server didn't know where it was from... sadly, if we were still playing by those rules today, I can only imagine how useless email would be. Now it's definitely guilty-till-proven-innocent.
The magic for me, to this day in fact, is knowing that mail is essentially anyone on the internet being allowed to write to a mail servers disk.<p>There are rules now, but the concept is still almost intact, random people writing to the servers disk - to be later read by someone
It used to be even more literally so - network mail started off as using FTP to SNDMSG onto a remote system instead of your own. In RFC475, FTP has MAIL and MLFL (mailfile) commands to support this.<p>I think it's neat that you can still find echoes of this. MAIL worked by just appending to MLFL, separating records with CRLF.CRLF - which is still how Data segments are terminated in SMTP.
With agents in the house now, we don't use curl at all. Slowly they all are becoming implementation details.
Yep! It’s all just text files. Lots of acronyms in top of lots of ways to generate, send, and read structured text files.<p>One day I realized even databases were just text files and I had to sit down.
Last century I would read and send personal email from work using telnet to pop3 and smtp respectively.
I also have a tendency to say "Last century", thinking it comedically suggests "a long time ago" without it actually <i>being</i> that long ago. But as time goes by it obviously becomes <i>legitimately</i> a long time ago, and I suspect young people wouldn't see the attempted irony at all.
You can actually do that today. In fact I did that for some time, because I didn't want to configure e-mail client. The only hard thing is HTML. Average HTML e-mail is almost impossible to read and friction to extract it to a file to open in a browser is too much.
perhaps you meant "in previous millennium" ?
If someone referred to the "previous decade" in 2004, would you have said the same thing?<p>As the calendar rolled from 1999 to 2000, we entered a new millennium, century, decade, year, day, ...
Yes, absolutely. I use the largest interval any time I can get away with it!<p>Every Jan 2 I start saying "last year" and every Dec I say "see you next year"
when you compare tech from 1999 and today, it does feel like new millennium tbh
><i>As the calendar rolled from 1999 to 2000, we entered a new millennium, century, decade, year, day, ...</i><p>no, that all happened when we rolled from 2000 to 2001.<p>smh, even paedants today aren't what they used to be.
The entirety of 1999 and 2000 was a nightmare. "No, buddy, we won't change millenium next january." "Nope. We are still in the 20th century." And so on...<p>I think that's more or less when I lost faith in humanity.
Presumably the years including 1999 and earlier
You can't do that with HTTP/2 (but thankfully every server still talks HTTP/1).<p>You also can't do that with TLS (and a lot of servers won't talk HTTP other than redirects). openssl s_client instead of telnet might allow you to tunnel text inside TLS, but that feels like a cheating.<p>And many other modern protocols, sadly, prefer binary encoding, which makes it impossible to tinker with it on wire level, not without specialized tools anyway.<p>I think people in the future will bother. I tried to make a fire with sticks once, I tried to burn a clay brick, these old things can be a lot of fun and sometimes of real use. If anything, AI actually makes tinkering a lot more easier. You don't need to dig into RFC to check your mail, you can just talk to LLM about it and it'll help you with most typical IMAP commands, for example.
openssl s_client -host google.com -port 443<p>You're welcome. Works like netcat plus TLS. Kind of inconvenient though. Hey someone should write tlsnc.
Nothing to regret. Text Protocol is too inefficient.
HELO is for SMTP, EHLO for ESMTP. You could access some “advanced” features of the server if you told it you speak ESMTP.
It was also cool discovering the ATA commands to drive the modem. You could “war-dial” numbers, or manually initiate Internet connection, or connecting to a bbs
Me too! Writing Winsock and learning WinAPI on XP then Vista. It took me a while to realise Linux was better / OSX was my gateway drug haha
I never figured out you could do it with HTTP, but for some reason I did for FTP and IRC. I don't know why I first tried using a telnet client but I couldn't believe it when the server responded to me!
I must have tried to write the same "perfect" IRC client from scratch in C a dozen times growing up...
When I was 12, I learned about open SMTP relays and how to spoof email this way. I once spoofed an email between two rivals on a community I was a part of and started a flame war.<p>Good times.
When I was in high school in the mid 2010s, Verizon's email-to-SMS gateway didn't verify SPF/DKIM/DMARC, and I had a field day showing my classmates the Viagra ads that Hillary Clinton's "hacked" email server was sending me. In reality, it was an open relay, but Verizon didn't care; they always delivered it anyway.
I once made an enemy on AOL and he was a spammer--he put my email in the from: field and I got a lot of hostile emails.<p>But the joke's on him--it led directly to me meeting a lifelong friend & mentor.
Isn't that the whole point of TCP? Creating a pair of two streams you can read out of and write to out of less reliable network primitives?<p>I am not sure why this is a revelation. Any college level networking course would cover this?!
> Any college level networking course would cover this?!<p>As an actual kid it's easy for it to be a revelation, no? At least it was for me, with no college level networking course experience.
> Perhaps most people in the future won't bother. They'll just let agents do it all.<p>But can you imagine the look on some young teen’s face when they train their own GPT on their local computer for the first time?
> This is a bash feature, not POSIX. dash (Debian’s /bin/sh) and zsh don’t have it, so a #!/bin/sh script can’t use it. Call bash directly.<p>Zsh has its own zsh/net/tcp and zsh/zftp modules.<p><a href="https://zsh.sourceforge.io/Doc/Release/TCP-Function-System.html" rel="nofollow">https://zsh.sourceforge.io/Doc/Release/TCP-Function-System.h...</a><p><a href="https://zsh.sourceforge.io/Doc/Release/Zsh-Modules.html#The-zsh_002fnet_002ftcp-Module" rel="nofollow">https://zsh.sourceforge.io/Doc/Release/Zsh-Modules.html#The-...</a><p><a href="https://zsh.sourceforge.io/Doc/Release/Zftp-Function-System.html" rel="nofollow">https://zsh.sourceforge.io/Doc/Release/Zftp-Function-System....</a>
In Plan 9 you did have a real (synthetic) /net, and could do that and more from any program. You could even mount /net from another machine via 9P protocol and have an instant VPN...<p>9front lets you play with that on Linux.<p>Some Plan 9 like /net things are visible in Go libraries... (Rob Pike legacy)
Neat, works against example.com<p><pre><code> exec 3<>/dev/tcp/example.com/80
printf 'GET / HTTP/1.1\r\nHost: example.com\r\nConnection: close\r\n\r\n' >&3
cat <&3
</code></pre>
Outputs:<p><pre><code> HTTP/1.1 200 OK
Date: Tue, 16 Jun 2026 17:37:45 GMT
Content-Type: text/html
...
</code></pre>
I always end up on example.com for this kind of thing because there are so few domains these days that don't enforce https!
example.com is also great for that reason when something fails about a captive portal on a public WiFi.<p>I open my web browser and go to <a href="http://example.com" rel="nofollow">http://example.com</a> and get redirected to the captive portal page again and retry completing what they need from me to get internet access.
Fun fact, this is almost exactly how active portal detection is done in the OS/browser!<p><a href="https://gist.github.com/skull-squadron/edb8c0122f902013304c031ebb01c1a1" rel="nofollow">https://gist.github.com/skull-squadron/edb8c0122f902013304c0...</a>
Yep :) I just find example.com easier to remember and quicker to type than any of the OS or browser makers own URLs like<p>- <a href="http://captive.apple.com/" rel="nofollow">http://captive.apple.com/</a><p>- <a href="http://connectivitycheck.gstatic.com/generate_204" rel="nofollow">http://connectivitycheck.gstatic.com/generate_204</a><p>- <a href="http://detectportal.brave-http-only.com/" rel="nofollow">http://detectportal.brave-http-only.com/</a><p>Plus, it feels nice to depend on the reserved domain name example.com instead of relying on a domain that any one specific corporation has to maintain :D
Also <a href="http://detectportal.firefox.com" rel="nofollow">http://detectportal.firefox.com</a>. And <a href="http://neverssl.com" rel="nofollow">http://neverssl.com</a> was set up for this purpose while being a bit easier to remember :)
What gives you confidence example.com won't start serving the HTTPS redirect though? There isn't any reason they wouldn't, and given that browsers are clearly tending towards showing big scary warnings to even accessing something over cleartext, I wouldn't be surprised if they flipped that switch just to avoid confusing noobs.
I have been using neverssl.com for this same purpose :)<p>My only concern would be that example.com doesn't promise to never do the 'required SSL' thing.
I use neverssl.com for this purpose because it is designed to resist caching.
This works too<p><pre><code> exec 3<>/dev/tcp/example.com/80
printf 'GET / HTTP/1.1\r
Host: example.com\r
Connection: close\r
\r
' >&3
cat <&3
</code></pre>
You can even take out the \r though they should be there
> As it turns out, bash can speak HTTP by itself.<p>No, it can not. Bash lets you open TCP sockets.<p>What you are doing here is trying to speak HTTP yourself, which is fine for testing and debugging, and hella cool for fun to do by hand, but you <i>will</i> shoot yourself in the foot if you try to use this pseudo http client unattended in reality. This toy code does not parse HTTP properly and <i>will</i> break.<p>You could of course write a full http/1.1 client in bash, you can even do a full http server in pure bash: <a href="https://github.com/bahamas10/bash-web-server" rel="nofollow">https://github.com/bahamas10/bash-web-server</a><p>For less insane, non-bash shells there is always nc which is usually probably the wiser choice.
Need to be clear that "full http server in pure bash" is incorrect. Bash cannot listen on a TCP/UDP socket for incoming connections.<p>bash-web-server project builds a C language socket listener [0] that is dynamically loaded at run-time as a "built-in" module that makes the functionality available.<p>[0] <a href="https://github.com/bahamas10/bash-web-server/tree/main/loadables" rel="nofollow">https://github.com/bahamas10/bash-web-server/tree/main/loada...</a>
This feature has been part of bash since 5.1 (ca 2020), though it may not be enabled in all distros.<p><pre><code> cd src/bash-5.3/examples/loadables
make accept
enable -f ./accept accept
(accept -r RHOST -v SOCKETFD -b 127.0.0.1 8000;
read -u $SOCKETFD SOCKETDATA;
printf "%s: %s\n" "$RHOST" "$SOCKETDATA";
printf "goodbye, world\n" 1>&${SOCKETFD} ) &
nc 127.0.0.1 8000 <<< "hello, world"
</code></pre>
For real use you may need to add "exec {SOCKETFD}<&-" to close the FD.<p>Edit: <a href="https://news.ycombinator.com/item?id=39369749">https://news.ycombinator.com/item?id=39369749</a> (2024)
By this logic, Linux does not support Wi-Fi, because all the driver modules are "dynamically loaded at run-time."
> No, it can not. Bash lets you open TCP sockets.<p>Very fair pushback -- I did get carried away and will update the article to be more precise. Thanks for raising it!<p>> For less insane, non-bash shells there is always nc which is usually probably the wiser choice.<p>For completeness, `nc` or any netcat equvialent I could think of was not available in the image I was trying this with. It would certainly be a better option though.
This is the most Claude pilled comment I've seen here.
This worries me. Some AI writing styles became mainstream; at first it was the em-dashes, now it’s “A, not B” patterns and excessive acknowledging. There will be more.<p>Was grandparent comment written by an LLM?<p>Or is this a human who copies a style they saw in a blog post, unaware that they’re copying an AI?<p>Or is this a human who spent too much time talking to an AI and now they just talk like this?<p>Or is this an organic human response and we’re all paranoid by now?<p>I don’t know which would be worse.
When learning a language, I've heard it's good to find a reference speaker, such as a prolific actor, and mimic them in order to absorb several aspects of what makes them sound authentic as a speaker, such as vocabulary, intonation, diction, pacing.<p>For many in the next generation of language learners, this reference will be Claude.
I think that the fact that AI has a very recognizable singular style is a problem. And this problem will be solved, sooner or later. It probably isn't a very important problem, because I feel that it should be relatively easy to solve (but maybe I'm wrong?).<p>But certainly with smarter AI I do believe it'll become more fluent with choosing more diverse idioms and phrasing, rather than repeating one thing over and over, to a point of being a comically similar. So people who learn on AI-generated text, will not learn from just one recurring style.
Insightful, and scary! Imitating an imitation machine... even if no one is <i>trying</i> to intentionally do so, McLuhan's "we become what we behold" is inescapable.
I'm going to go insane from all of this
So? That's literally how language works. The importance is not in the writing style, but in the content of the words.
It's pretty rough to learn I sound like Claude. Will need to do something about it then.<p>(For what it's worth I did write the message above manually but I understand why no one would believe that now. At least I did not call netcat "load-bearing" [<a href="https://mareksuppa.com/til/load-bearing/" rel="nofollow">https://mareksuppa.com/til/load-bearing/</a>] or something...)
I did not think you sounded like claude. Then I looked again after the comment was made and then I saw some of the vibes. Like acknowledging a mistake you have done.<p>Before that would just made you top 5% (or maybe top 1%) of the nicest people to talk too.. know ppl think you are Claude.<p>We are all going crazy s a sibling comment said.
I know that feeling<p>I notice myself getting afflicted with llm-isms after a full workday. And I didn't always notice, sometimes I only realize the day after...<p>Like it slowly siphoned out my soul, which then reconnected with me over night
Avoid the backtick quotes, too. Claude also mistakenly uses them outside of markdown.
Ok Claude :)
[dead]
I’m torn. It’s a great thing to share knowledge and take feedback graciously. Maybe this kind of comment will encourage more of that. But you also need people to tell you what is up without unnecessary filters. It’s a challenge
what would be a non-pilled way of saying the same thing?
FWIW, I didn't read this as AI-like. Even on a re-read, it's only the quasi-em-dash, and _maybe_ the polite acknowledgement of "Very fair pushback" (just good etiquette, IMO!) that would ring any alarm bells. You're fine.
[flagged]
it's not that insane. i've been manually typing http requests in since before http/1.1 and the mandatory host header.<p>it is insane to use it for anything serious (also the opposite, implementing webservers in bash), but for quick testing it's pretty great!
Someone did a Minecraft server in pure bash.<p><a href="https://sdomi.pl/weblog/15-witchcraft-minecraft-server-in-bash/" rel="nofollow">https://sdomi.pl/weblog/15-witchcraft-minecraft-server-in-ba...</a>
There's even a Rails-like framework for Bash: <a href="https://github.com/jneen/balls" rel="nofollow">https://github.com/jneen/balls</a>
>No, you can't write 10 lines of code, you have to import a 100k LOC dependency<p>Common misconception, if you want to replace a dependency on a swiss knife you don't need to implement a swiss knife, sometimes you can just implement the last helix of the corkscrew.
Nice parameter expansion examples in that bash-web-server. It uses the $_ parameter in ways I hadn’t thought to before, often preceded by a single : ${x} line for pre-processing of the variable.
> No, it can not. Bash lets you open TCP sockets.<p>I thought you had to use a program called netcat for that--if not then what is the point of that binary? And for that matter, can't you also use telnet to manually send HTTP?
[dead]
I ran into this while checking connectivity between containers on an internal Docker network where the image had neither curl nor wget.<p>The main surprise was that Bash has /dev/tcp which lets you do the equivalent of an HTTP request with a bit of shell magic, for instance:<p><pre><code> exec 3<>/dev/tcp/service/8642
printf 'GET /health HTTP/1.1\r\nHost: service\r\nConnection: close\r\n\r\n' >&3
cat <&3
</code></pre>
Where `service` is just the hostname of whatever you’re talking to and 8642 is the port you are trying to talk HTTP to.<p>Pretty cool!
It seems pretty cool, but I am wondering if there's any drawback on just using images that support curl? I can't think of any and to me it's kinda a must have, even on production images
I always recommend to not have any dependencies outside of the code.<p>So we start at compiling the codebase (Rust) against MUSL. That way we can run it with FROM scratch images.<p>If we need more tooling available at runtime, then we look at alpine, but still using MUSL.<p>If MUSL itself is proving problematic, or if some of the libraries we use need glibc then we can look at using some locked down image.<p>The cool part about FROM scratch images is that you'll never have to update your base image to address CVEs. Only your software and its (compiled) dependencies.
> The cool part about FROM scratch images is that you'll never have to update your base image to address CVEs. Only your software and its (compiled) dependencies.<p>What's the benefit really, though? If you still need to be able to rapidly deploy a new image in response to a dependency CVE, what have you gained?
You've gained that happening much less frequently. The tradeoff is making every other problem harder to diagnose.
Debug containers are a thing.<p><i>Add an ephemeral container to an already running pod, for example to add debugging utilities without restarting the pod.</i><p><a href="https://kubernetes.io/docs/reference/kubectl/generated/kubectl_debug/" rel="nofollow">https://kubernetes.io/docs/reference/kubectl/generated/kubec...</a>
If the base image I use is based on Debian, it comes with more than 15 binaries that I don't use.<p>But when Docker scans my image and notices that there is a CVE in one of those binaries, my image is currently out of compliance.<p>FROM scratch just reduces the surface.
preface: I'm not asking things rhetorically, I genuinely want to learn here.<p>> to not have any dependencies outside of the code.<p>> ... FROM scratch images is that you'll never have to update your base image to address CVEs...<p>So a FROM scratch image, basically doesn't have things like a package manager to install things, and maybe also libraries that things like curl would depend on? Sorry for my ignorance, I've heard of FROM scratch but never tried them.
Apparently you get only an empty root directory, nothing else. <a href="https://medium.com/@fabrizio.sgura/the-forgotten-minimalist-exploring-dockers-from-scratch-image-f1254049def2" rel="nofollow">https://medium.com/@fabrizio.sgura/the-forgotten-minimalist-...</a>
More than one ~500 employee company I've worked at has had security policies either encouraging or requiring the use of "distro-less" images - images with no OS components other than the absolute minimum required to run the application. For go binaries this meant literally nothing in the container apart from the executable.<p>In theory it has a couple of benefits. You don't have to re-deploy your image to patch CVE's in OS components if you don't have any OS components. And it provides some measure of defence-in-depth - one could certainly theory-craft a scenario where an attacker gains some limited control over your application and then uses some OS component to escalate.<p>These days if a security engineer is proposing my team adopt distro-less containers to receive these benefits, I would point out that we need to weigh them against the very real drawbacks of not having standard debugging tools available where and when we need them. And also to consider the relative impact of other defence-in-depth measures they could be pursuing instead - such as any sort of network policy to limit network traffic.
> not having standard debugging tools available where and when we need them<p>Keeping in mind that containers are merely a bunch of namespaces, there's nothing stopping you from entering the same PID namespace with a different mount namespace in order to debug.
I am aware, thank you :). I responded to a sibling dupe-comment over here [1].<p>To summarize, in my experience there is immense value to having basic shell tools available in the environment where you need them with zero extra friction. Stripping those out provides a security benefit only in specific nebulous and niche scenarios.<p>1: <a href="https://news.ycombinator.com/item?id=48561605">https://news.ycombinator.com/item?id=48561605</a>
> in my experience there is immense value to having basic shell tools available in the environment where you need them with zero extra friction<p>I agree, however assuming you maintain a chroot for debugging this can be accomplished with a shell command that takes a single argument to target a running container by name.<p>Your linked comment suggests being limited to kubernates but nsenter and a chroot are entirely runtime agnostic.
Debug containers are a thing.<p><i>Add an ephemeral container to an already running pod, for example to add debugging utilities without restarting the pod.</i><p><a href="https://kubernetes.io/docs/reference/kubectl/generated/kubectl_debug/" rel="nofollow">https://kubernetes.io/docs/reference/kubectl/generated/kubec...</a>
That is indeed a solid pushback! :)<p>For what its worth, this container used `python:3.12.2-slim-bookworm` and I really would not expect that sort of an image to bundle `curl` -- even if it is intended for production.
You can also use the sockets lib in that case, you depend on POSIX instead of Linux
Ah I see so it was basically a minimal image that bundles just python? I can see why it wouldn't bundle curl! Thought it was a custom Image for some reason, hence my original comment
It’s handy when you’re troubleshooting issue on a running container which you can’t just rebuild the image and reload
This of course only supports http, not https. It's great for health checks e.g. in a docker environment. To do https, you'd have to use something like socat, but of course that doesn't use bash only.
You might not have any say on what image is in use, for example, in a cicd library project.
It's also a two line Dockerfile to add wget or curl to almost any pre-existing container image. This is a fun idea though.
Note that this didn't work historically on Debian, and presumably Debian-derived distros, where the virtual file TCP access was disabled by default. The position was reversed (and the capability enabled) in 2009, AFAIU. There's discussion and links in Bug #146464:<p><<a href="https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=146464#37" rel="nofollow">https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=146464#37</a>><p>As others have mentioned, there are numerous other ways to directly access network features using shell tools, including curl (noted in TFA's title), wget, the HEAD and GET commands (from Perl), netcat (nc), socat, telnet, and I'm quite sure others.
A few years ago I had to do this for a SpringBoot health check from a Docker container:<p>FROM openjdk:11-jre-slim
HEALTHCHECK --start-period=10s --timeout=3s --retries=5 \
CMD perl -e "use IO::Socket; $sock = IO::Socket::INET->new(Proto => 'tcp', PeerAddr => 'localhost', PeerPort => '8888') or die $@; $sock->autoflush(1); print $sock 'GET /actuator/health HTTP/1.1' . chr(0x0a) . chr(0x0d) . 'Host: localhost:8888' . chr(0x0a) . chr(0x0d) . 'Connection: close' . chr(0x0a) . chr(0x0d) . chr(0x0a) . chr(0x0d); while (my $line = $sock->getline ) { if ($line =~ /UP/) {exit;} }; close $sock; exit 1;"
Oh man this would have saved me quite some time trying to include curl in my initramfs image with busybox that fires off a request to notify me to login via dropbear to put in the LUKS key. In the end the copy_exec script worked well though and i do have https
For the next level unlock try to make a HTTP/3 request over /dev/udp.
For a light-weight aliveness check or something like that this is perfectly fine approach.<p>Just like parsing HTML with regexes can be fine too - for instance if you know the sender.<p>Just like repeating code can be fine too, even though it violates DRY.<p>Mixing markup and code can be fine (call it Locality of Behavior).<p>But separating markup and code is fine too (Separation of Concerns).<p>goto’s can be a lifesaver for deeply nested error conditions in C.<p>The point is all these “you shouldn’t do this” comments are just generalities. Use your judgement, decide if the tradeoffs are right and make a deliberate choice.
I would use HTTP/1.0 without a need for Connection: close. Unless 1.0 is not generally supported anymore, but this is not the case in my experience.
The 90s are calling. Its a bit funny when 30 years or so later people rediscover linux functionalities.
You could also use nsenter if curl is installed on the host, eg<p>docker inspect -f '{{.State.Pid}}' container-name<p># let's imagine that outputs 814538<p>nsenter -t 814538 -n curl example.com
It is nice for a basic port knocking as well.<p><pre><code> timeout 5s bash -c "echo >/dev/tcp/google.com/443" && echo "port open" || echo "port closed"
</code></pre>
This uses the timeout command from coreutils though, so it is not a pure bash implementation.
It is a KornShell feature since ca. 1997<p><a href="https://github.com/ksh93/ast-open-archive/blame/master/src/cmd/ksh93/sh.1" rel="nofollow">https://github.com/ksh93/ast-open-archive/blame/master/src/c...</a>
This is pretty neat if all you need is to ping a local server but please use curl (or something equivalent) for contacting remote services. HTTP1.1 seems like such a simple protocol but in the real world you need to deal with proxies, different encodings, and redirects. Curl takes care of that (and a host of other annoying stuff) for you.
Totally!<p>I was really just trying to see if intra-container connectivity works, and this ended up being a very quick way of doing so. (The alternative being building and deploying a new image, which would likely take significantly longer.)
> The alternative being building and deploying a new image, which would likely take significantly longer<p>You said the image was Python, though? Using that is way easier and faster. <a href="https://news.ycombinator.com/item?id=48558763">https://news.ycombinator.com/item?id=48558763</a><p>If all you need to know is that it can connect:<p>python3 -c 'import socket as s;s.create_connection(("8.8.8.8",53))'<p>or http:<p>python3 -c 'from urllib.request import*;print(urlopen("<a href="http://example.com").status" rel="nofollow">http://example.com").status</a>)'
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At a past job the security team wouldn't let us have netcat or curl on our systems. So I just used /dev/TCP to get around that. The ergonomics were not as nice as using netcat or curl, but it got the job done.
TIL: bash and other shells try to copy Plan 9's /net directory and the kernel ip(3) file server. Too bad it's not a real file system. And a missed opportunity to call the root of the path /net.
It was fun exploring this to make a native-shell-only peer-to-peer file transfer utility at work for some automation scripts. At least, it was until trying to replicate it in Powershell was somehow triggering Crowdstrike and the corporate Cybersecurity team thought I was writing malware.
Fun story: A few years ago, I worked for a small company that customized off the shelf routers to enable businesses provide Wifi Hotspots.<p>The routers were very basic model with very limited flash memory (~4MB?). I was brought in to build firmware for those routers. I ended up customising openwrt - removed all kinds of packages to make their packages fit on those routers. At the end, I had less than 4KB space, And I needed to implement a "heart beat" service. A lot of routers were behind firewalls that only allowed http, https and a couple of other protocols. Libcurl was too heavy. So I ended up writing a shell script that used this feature of bash to send out heart beats.<p>Fun times...
There is a whole talk on how to use it even for interactive sessions.<p><a href="https://youtu.be/hBcfrQ8y5Qg?is=Osjnhjrx7WgsHqVj" rel="nofollow">https://youtu.be/hBcfrQ8y5Qg?is=Osjnhjrx7WgsHqVj</a>
It's interesting that most of the comments here are about using this feature to bypass security restrictions (whether valid or not). It says a lot about the attack surface of GNU utilities caused by featuritis.
This is the kind of content we all deserved in 2026, and this is still why I ask during interviews to explain how cookies are represented in HTTP protocol.
This is an old post-compromise trick used when an attacker needs to download a payload or make a network connection and curl, wget and nc are all not available.
This was something I learned about 10 years ago when earning my OSCP, useful during penetration tests and CTFs when you get a low-priv shell that's running a minimal OS (No curl, nc, python, etc.) but running a web server listening on localhost.<p>Using /dev/tcp was also handy in getting that initial low-priv shell.
Thanks! I dislike this
Once had a coworker tell me to never to use this because "you never know when the customer doesn't have bash installed; use python instead" even though our contract required that the customer had bash. I'm still laughing at that.
FWIW, some distributions (I forget which ones, but I've seen it more than once) compile bash without the network features. Python is ubiquitous, and I've never seen it subsetted this way, so I'd have sided with the coworker.
Eh, looking around, I think you're thinking of Debian. They re-enabled it by-default back in 2009. So, sure, I guess. But if you're dealing with an OS that's from 2009 these days, whether /dev/tcp is enabled in bash or not isn't exactly relevant anymore. And I've seen enough broken python installs (even with stdlib) to put my faith in /dev/tcp working in bash :)
I discovered this bash trick by chance when I was once trying to healthCheck the Envoy's official OCI image container which didn't include curl or wget while forcing the envoy admin interface to listen on localhost which breaks the traditional k8s httpGet checks.
interesting attack vector<p>shame it's not a real device so the surface is limited to bash only<p>I wonder what software might be vulnerable to this attack surface
I love that under Linux your tcp stack is a file.
It's a fun trick, but I really don't like that bash does this. It's such an un-clean interface, and I'm not aware of any use cases beyond trying to exfiltrate data from a badly locked-down shell.
Reminds me of telnetting to port 80 to make a get request years and years ago
I find /dev/udp much more useful. I can create aliases for fire and forget commands to my daemons without actually writing *ctl program.
You don't need Connection: close if you use HTTP/1.0.
Yes, it used to be my goto few times when some devices tried to lockdown everything with bare minimum core utils and no network capable tools like curl etc.
I actually have a couple of Dockerfiles that are using exactly this in the HEALTHCHECK. Less packages to install.
That's pretty neat, thanks for sharing
> This is a bash feature, not POSIX. dash (Debian’s /bin/sh) and zsh don’t have it, so a #!/bin/sh script can’t use it. Call bash directly.<p>This is why we can’t have nice things. This feature is complex and obscure enough that you are unlikely to be able to use it manually without consulting a reference, and poorly supported that any script you write with it is unportable.<p>Bash is so powerful and so frustrating for this reason all the time :(
why bother with /dev, all you need is a battery, a couple of needles and some length of ethernet cable
At least on my systems there's also /dev/udp...
brb. recompiling bash in all my base images.
Reminds me of using telnet to port 80 to make get requests aeons ago
Welcome to the year 2000.
This is a cool trick.<p>I discovered it for myself some years ago, when I wanted to make simple network test scripts run without depending on curl or telnet, or other executables outside of bash.
Then TLS, HTTP/2, and HTTP/3 enter the chat, and now you can’t just send a request.
telnet then?
Wait until they hear about Plan 9!
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