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TIL: You can make HTTP requests without curl using Bash /dev/TCP

mareksuppa.com

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Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#61

Post by saidinesh5 »

Fun story: A few years ago, I worked for a small company that customized off the shelf routers to enable businesses provide Wifi Hotspots.

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.

Fun times...

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#62

Post by LeoPanthera »

QuantumNomad_ wrote: post #26
simonw wrote: post #16

Neat, works against example.com 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 Outputs: HTTP/1.1 200 OK Date: Tue, 16 Jun 2026 17:37:45 GMT Content-Type: text/html ... 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. I open my web browser and go to http://example.com and get redirected to the captive portal page again and retry completing what they need from me to get internet access.

I use neverssl.com for this purpose because it is designed to resist caching.

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#63

Post by cyanydeez »

TZubiri wrote: post #47
basilikum wrote: post #8

> As it turns out, bash can speak HTTP by itself. No, it can not. Bash lets you open TCP sockets. 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 will 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 will break. You could of course w…

>No, you can't write 10 lines of code, you have to import a 100k LOC dependency 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.

it's curious what you'd be building where you think you can hit the reliability of curl with a bash script.

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#64

Post by xmodem »

OptionOfT wrote: post #57
xmodem wrote: post #21

Earlier quoted context omitted.

> 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. 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?

If the base image I use is based on Debian, it comes with more than 15 binaries that I don't use. 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. FROM scratch just reduces the surface.

> FROM scratch just reduces the surface.

The actual attack surface of your application? Or the attack surface of you and your team's attention from a busybody security org.

It's important not to confuse the two.

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#65

Post by pillmillipedes »

cyanydeez wrote: post #63
TZubiri wrote: post #47

Earlier quoted context omitted.

>No, you can't write 10 lines of code, you have to import a 100k LOC dependency 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.

it's curious what you'd be building where you think you can hit the reliability of curl with a bash script.

a script ten lines long perhaps?

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#66

Post by 8bitsout »

thih9 wrote: post #31
bearjaws wrote: post #20

Earlier quoted context omitted.

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. Was grandparent comment written by an LLM? Or is this a human who copies a style they saw in a blog post, unaware that they’re copying an AI? Or is this a human who spent too much time talking to an AI and now they just talk like this? Or is this an or…

I'm going to go insane from all of this

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#67

Post by nandomrumber »

basilikum wrote: post #8

> As it turns out, bash can speak HTTP by itself. No, it can not. Bash lets you open TCP sockets. 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 will 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 will break. You could of course w…

[dead]

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#68

Post by xenadu02 »

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.

Simple get: GET / HTTP/1.1 Content-Type: text/html User-Agent: l33t hax0rs lol X-Funny-Monkey: farts

For sending a mail message on port 25: HELO mail-from: whoever@whatever.com mail-to: sysadmin@yaya.com Body of the message yay.

POP3 was so long ago I forgot but you could list the mailboxes then get individual messages and so on.

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.

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).

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#69

Post by andelink »

basilikum wrote: post #8

> As it turns out, bash can speak HTTP by itself. No, it can not. Bash lets you open TCP sockets. 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 will 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 will break. You could of course w…

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.

Re: TIL: You can make HTTP requests without curl using Bash /dev/TCP

#70

Post by ffsm8 »

mrshu wrote: post #52
bearjaws wrote: post #20

Earlier quoted context omitted.

This is the most Claude pilled comment I've seen here.

It's pretty rough to learn I sound like Claude. Will need to do something about it then. (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" [ https://mareksuppa.com/til/load-bearing/ ] or something...)

I know that feeling

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...

Like it slowly siphoned out my soul, which then reconnected with me over night

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