Piping prevents commands from fully executing?

Why is it, that when I pipe a command into another command, the other command doesn't fully execute? Like if I run

echo -e -n "localhost / 0\r\n" | nc localhost 301

or

echo -e -n "localhost / 0\r\n" | nc -w 100s localhost 301

it does not output the response from localhost, or even wait for 100 seconds and timeout, it just exits. Why is this?

Posted in: s/bash

🚀 asdf

Mar 01 · 4 months ago

6 Comments ↓

🤖 BBSman · Mar 01 at 13:56:

`nc` exits immediately when it can't connect to the specified host & port.

🚀 asdf [OP] · Mar 01 at 14:51:

@BBSman that is irrelevant since "nc localhost 301" does connect.

🚀 jsreed5 · Mar 01 at 15:57:

What do you see if you run `nc -vz`? nc might be encountering some other error that it's not reporting.

🚀 asdf [OP] · Mar 01 at 16:07:

@jsreed5 running "nc -vz" by itself outputs the following message:

Ncat: Version 7.93 ( https://nmap.org/ncat )

Ncat: You must specify a host to connect to. QUITTING.

running

echo -e -n "localhost / 0\r\n" | nc -vz localhost 301

does not output anything

Edit: I'm a dumbass, accidentally ran it with a greater than sign instead of a pipe (I just went through my bash history until I found the command so I could add the -vz but I edited the wrong command)

the output from

echo -e -n "localhost / 0\r\n" | nc -vz localhost 301

was actually

Ncat: Version 7.93 ( https://nmap.org/ncat )

Ncat: Connected to ::1:301.

Ncat: 0 bytes sent, 0 bytes received in 0.22 seconds.

It's strange, because when running "nc localhost 301" it does respond, so it shouldn't say "0 bytes received"

🚀 clseibold · Mar 01 at 21:19:

@asdf Is this connecting to spartan server?

🚀 asdf [OP] · Mar 02 at 07:10:

@clseibold yes