grep with continuous pipe does not work

Question

(maybe it is the \"tcpflow\" problem)

I write a script to monitoring http traffic, and I install tcpflow, then grep

it works (a

Answer 1

To grep a continuous stream use --line-buffered option:

sudo tcpflow -p -c -i eth0 port 80 2> /dev/null | grep --line-buffered '^Host'

--line-buffered

Use line buffering on output. This can cause a performance penalty.

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Some reflections about buffered outputting(stdbuf tool is also mentioned):

Pipes, how do data flow in a pipeline?