LinuxQuestions.org - Piping to telnet 80 failing

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Piping to telnet 80 failing

We're using a dynamic dns providor's script (referring to the CGI) to update our IP address (by their instructions) like so:

Code:

telnet host.com 80

GET /ip.cgi?host=our.host.com&key=g1c48672b5ba99d49d0a684aaac58b56

OK Host updated

However, when I do this from the shell, nothing works:

Code:

export DOMAIN_COMMAND="GET /ip.cgi?host=our.host.com&key=g1c48672b5ba99d49d0a684aaac58b56"

( sleep 1 ; echo $DOMAIN_COMMAND ; echo exit ) | telnet host.com 80

Trying host.com

Connected to host.com

Escape character is '^]'.

where it breaks

Connection closed by foreign host.

I get immediately dropped (well, after the sleep 1). Any ideas why entering the command long-hand works but passing it via a pipe doesn't ? Even a simple "echo 'GET /'" doesn't work.

Using a pipe in this context is simply sending bunk input to telnet. You need to use 'nc' (AKA netcat).

Code:

( sleep 1 ; echo $DOMAIN_COMMAND ; echo exit ) | nc host.com 80

Thanks, I never thought of that !

I read a reply to someone asking how to log in automatically over telnet, and he used this method (i.e., my bad method) to enter username, password, etc. I guess it didn't work.