More on Using Bash's Built-in /dev/tcp File (TCP/IP)
If you saw yesterday's Tech Tip and were looking for more on using TCP/IP with bash's built-in /dev/tcp device file then read on. 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]]... If command is not specified, any redirections take effect in the current shell, and the return status is 0.
So using exec without a command is a way to open files in the current shell.
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 <!doctype html><html><head><meta ...
And that's it, with just a few more lines of code you could have your own bash based browser... well maybe not.
Mitch Frazier is an Associate Editor for Linux Journal.
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
Free to Linux Journal readers.Register Now!
- SourceClear Open
- SUSE LLC's SUSE Manager
- My +1 Sword of Productivity
- Managing Linux Using Puppet
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- Non-Linux FOSS: Caffeine!
- Tech Tip: Really Simple HTTP Server with Python
- Doing for User Space What We Did for Kernel Space
- Google's SwiftShader Released
- Parsing an RSS News Feed with a Bash Script
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide