Question

I’m trying to play around with netcat to learn more about how HTTP works. I’d like to script some of it in bash or Perl, but I’ve hit upon a stumbling block early on in my testing.

If I run netcat straight from the prompt and type in a HEAD request, it works and I receive the headers for the web server I’m probing.

This works:

    [romandas@localhost ~]$ nc 10.1.1.2 80     HEAD / HTTP/1.0      HTTP/1.1 200 OK     MIME-Version: 1.0     Server: Edited out     Content-length: 0     Cache-Control: public     Expires: Sat, 01 Jan 2050 18:00:00 GMT      [romandas@localhost ~]$

But when I put the same information into a text file and feed it to netcat through a pipe or via redirection, in preparation for scripting, it doesn’t return the headers.
The text file consists of the HEAD request and two newlines:

HEAD / HTTP/1.0  

Sending the same information via echo or printf doesn’t work either.

$ printf 'HEAD / HTTP/1.0\r\n'; |nc -n 10.1.1.2 80 $ /bin/echo -ne 'HEAD / HTTP/1.0\n\n' |nc 10.1.1.2 80

Any ideas what I’m doing wrong? Not sure if it’s a bash problem, an echo problem, or a netcat problem.

I checked the traffic via Wireshark, and the successful request (manually typed) sends the trailing newline in a second packet, whereas the echo, printf, and text file methods keep the newline in the same packet, but I’m not sure what causes this behavior.

Answer 1

You need two pairs of "\r\n", and also to tell netcat to wait for a response.

The following or something similar should work:

printf "HEAD / HTTP/1.0\r\n\r\n" | nc -n -i 1 10.1.1.2 80