linux FIFO block on read

Question

I'm doing exercise net0 on https://exploit-exercises.com/protostar/. The content of the exercise is to send requested number as a little endian 32bit int to the server. I came up with the following command lines.

mkfifo /tmp/pipe  
cat /tmp/pipe | netcat 127.0.0.1 2999 |tee -a /tmp/log | cut -d ' ' -f 3 | xargs -I{} python -c "import struct; print struct.pack('I',int({}))" > /tmp/pipe

The second command line doesn't finish, and I found cat /tmp/pipe blocking on read (not on open) when use strace to debug.

@aLeX and test comamnd line `echo "Please send '220419784' as a little endian 32bit int" | cut -d ' ' -f 3 | xargs -I{} python -c "import struct; print struct.pack('I',int({}))" ` outputs the right answer. — dcnh35, Apr 16 '18 at 02:37

dcnh35 · Answer 1 · 2018-04-16T15:24:28.170

1

I found the reason. when the output is not terminal, cut will buffer the output. python print also needs to be flushed. https://unix.stackexchange.com/a/226675/194577

edited Apr 16 '18 at 15:24

answered Apr 16 '18 at 15:14

dcnh35

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linux FIFO block on read

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