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Three classic command line tips

17 October 2009

Gosh it has been a long time since my last post, life sucks sometimes. Lets get back into it with three golden oldies.

Downloading a real player file

Saving a real player stream takes two steps. Firstly you download the metadata file, this is a text file, normally ending with .ram.

wget http://link-to-realplayer-metadata-file.ram

Opening this file in a text editor, or by using the cat command will show a link such as:

rtsp://blah-blah-blah/blah/blah.ra

Using the following command line arguments, you can now download the stream with mplayer:

mplayer -noframedrop -dumpfile localfile.rm -dumpstream rtsp://blah-blah-blah/blah/blah.ra

Checking your HTTP headers

After fiddling with the configuration of your http server (e.g. Apache), you should check that it is supplying the correct headers. A quick and easy way is to use telnet.

To open the connection, you use:

telnet commandline.org.uk 80

Then lets check the http header for a basic HTML page, copy and paste both lines:

HEAD // HTTP/1.1
Host: commandline.org.uk

Now lets look at an image.

HEAD /images/posts/chess/matchreport/20081025/17.png HTTP/1.1
Host: commandline.org.uk

You can also get the whole page:

GET / HTTP/1.1
Host: commandline.org.uk

You can have hours of fun with telnet!

Giving Java some more juice

Regular readers will know I love using programming languages beginning with P, but I do regularly use little Java programmes written by my friends, which I run in the following way:

java -jar programname.jar

However, I find myself in the situation where the program will die due to lack of memory.

If it runs out of memory, then let it have more:

java -Xms128m -Xmx750m -jar programname.jar

The -Xms argument sets the initial heap size to 128 MB, the -Xmx sets the maximum heap size to 750 MB.

Now all your bloated, poorly-written Java programs can use up as much memory as they need.

1 Brandon says...

BTW, you can combine the "Downloading a real player file" hint into a single command that only depends on the .ram file.

mplayer -noframedrop -dumpfile localfile.rm -dumpstream $(curl --silent http://link-to-realplayer-metadata-file.ram)

Posted at 9:40 p.m. on October 17, 2009


2 bug says...

People still use Real Player?

Posted at 9:20 a.m. on October 18, 2009


3 David Jones says...

As well as telnet, I also use "curl -I" for inspecting headers. Although it has a ridiculously long man page, it's slightly easier for poking about with certain client options:

curl -I http://www.amberfrog.com/logo/

(look ma, real XHTML)

Posted at 11:54 a.m. on October 18, 2009


4 Zeth says...

Thanks for the comments guys. Great to see the all the gang are still here!

Posted at 7:20 p.m. on October 18, 2009


5 Jim says...

Thanks for the rtsp:// post - that's something that has been bugging me for a while!

Posted at 2:30 p.m. on October 19, 2009


6 Ken says...

Stumbled in here at lunch. This is the best find of the week. Thanks.

Posted at 5:59 p.m. on October 21, 2009


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Hello, my name is Zeth, I'll be your host here.

Command Line Warriors is about taking control of your own technology, it looks at our experiences of computing; especially using GNU/Linux, the Python programming language, the command-line and issues such as techno-ethics, best practices and whatever is cool now. If you take control of your technology then you are a Warrior too!

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Stumbled in here at lunch. This is the best find of the week. Thanks.
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Thanks for the rtsp:// post - that's something that has been bugging me for a while!
→ Three classic command line tips

Zeth

October 18, 2009
Thanks for the comments guys. Great to see the all the gang are still here!
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Bubba

October 18, 2009
Is there any way psftp can return the true transfer rates oberved during the actual transfer?
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