Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

mareksuppa.com

Post reply on HN
Print view View original

21–30 of 255 posts

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

#21

Post by xmodem »

OptionOfT wrote: post #18
sevenzero wrote: post #3

Earlier quoted context omitted.

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. So we start at compiling the codebase (Rust) against MUSL. That way we can run it with FROM scratch images. If we need more tooling available at runtime, then we look at alpine, but still using MUSL. 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. The cool part ab…

> 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?

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

#22

Post by morpheuskafka »

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, it can not. Bash lets you open TCP sockets.

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?

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

#24

Post by [deleted] »

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…

[deleted]

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

#25

Post by orthogonal_cube »

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.

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

#26

Post by QuantumNomad_ »

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.

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

#27

Post by geoctl »

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.

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

#28

Post by sam_lowry_ »

A few years ago I had to do this for a SpringBoot health check from a Docker container:

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;"

Post reply on HN