Here, we'll both read from, and write to a socket. Before I go any further, let me state that this is based on something I discovered here on Dave Smith's Blog.
All I've done here is added a few improvements based on the comments to the original post. I've also added a bit of additional explanation.
The following script fetches the front page from Google:
exec 3<>/dev/tcp/www.google.com/80 echo -e "GET / HTTP/1.1\r\nhost: http://www.google.com\r\nConnection: close\r\n\r\n" >&3 cat <&3
Pretty simple, just 3 lines.
The first line may be a bit confusing if you haven't seen this type of thing before. This line causes file descriptor 3 to be opened for reading and writing on the specified TCP/IP socket. This is a special form of the exec statement.
From the bash man page:
exec [-cl] [-a name] [command [arguments]]So using exec without a command is a way to open files in the current shell.
... If command is not specified, any redirections take effect in the current shell, and the return status is 0.
After the socket is open we send our HTTP request out the socket with the echo ... >&3 command. The request consists of:
GET / HTTP/1.1 host: http://www.google.com Connection: close
Each line is followed by a carriage-return and newline, and all the headers are followed by a blank line to signal the end of the request (this is all standard HTTP stuff).
Next we read the response out of the socket using cat <&3, which reads the response and prints it out. The response being the main HTML page from Google:
$ bash tcp.sh HTTP/1.1 200 OK Date: Wed, 30 Sep 2009 17:28:36 GMT Expires: -1 Cache-Control: private, max-age=0 Content-Type: text/html; charset=ISO-8859-1 Set-Cookie: PREF=ID=... Set-Cookie: NID=27=... Server: gws X-XSS-Protection: 0 Transfer-Encoding: chunked Connection: close fef
And that's it, with just a few more lines of code you could have your own bash based browser... well maybe not.