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In order to redirect the tcp connections with bash, why the following commands return nothing?

[root@rocks7 ~]# echo -e "GET / HTTP/1.1\n\n" > /dev/tcp/yahoo.com/80
[root@rocks7 ~]# printf "GET / HTTP/1.1\n\n" > /dev/tcp/google.com/80
[root@rocks7 ~]# 
  • 1
    Because you are sending but not reading? – ajeh Apr 25 '18 at 15:51
  • If you want to receive too, install socat and try something like echo -e "GET / HTTP/1.1\n\n" | socat STDIO TCP:google.com:80 – Torin Apr 25 '18 at 16:31
2

You need to open the connection for read and write, using <>, and probably send a few more headers, then read the reply. For example,

exec 5<>/dev/tcp/yahoo.com/80
echo -e "GET / HTTP/1.1\r\nHost: yahoo.com\r\nContent-Length: 0\r\n\r" >&5
# get reply:   HTTP/1.1 301 Moved Permanently^M
cat <&5

I used arbitrary file descriptor 5 just to avoid clobbering the standard 0, 1, and 2. With yahoo you don't need the content length header, but other sites might not reply until they have received more input. yahoo does require the host header, or you will get the reply HTTP/1.1 400 Host Header Required.

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