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A useful technique to know about when using Linux is to run commands in the background. Sometimes certain commands can either take a while (like copying a large file) or will simply take over the terminal window when run. For example, lets say that you open a file in gedit, you might use the following command.

gedit file.txt

Doing this will open the file in gedit but will not allow you to do anything in the terminal window until you close gedit. To open the file but still keep the terminal window active use the & symbol at the end of the command. This will run the proceeding command in the background.

gedit file.txt&

To run a file copy in the background do the following.

cp file.txt file.txt.bak&

Note that this command shouldn't be used for all commands, especially those that produce some form of output. For example, running the following command

Removing the last line from a file is an easy process and can be done in just a few lines of code.

XML data extraction can be a common task, but to work directly with this data you need to understand how PHP parses XML. There are various different functions involved in parsing XML in PHP, all of which work together to extract data from a XML document. I will go through each of these functions and tie them together at the end.

xml_parser_create()

This function is used to create the parser object that will be used by the rest of the process. This object is used to store data and configuration options and is passed to each of the functions involved.

$xml_parser = xml_parser_create();

xml_set_element_handler()

Next we need to set up the functions that will be used in the parsing of the script. The xml_set_handler() method takes the following parameters:

Whilst creating a small plugin on a Wordpress site I decided not to use the media library as I just wanted to add some small stub images to the content. I created some boxes on the post page using add_meta_box() and added a file input box to them. The only thing is that the post form in Wordpress doesn't have the enctype="multipart/form-data" attribute and so it won't pass file to the $_FILES array in PHP.

It is not possible to add the enctype into the form declaration via Wordpress as there is no hook or action to do this. So the only alternative (rather than hack the source code) is to add the attribute using JavaScript, and as we have JQuery already loaded we can utilise that.

When moving a Wordpress install from one place to another there are a number of things you must be aware of. If you have created your templates properly you will have used calls to bloginfo('home') rather than using static links, but you will need to update these links to make your Wordpress install work properly.

Once the files are in place, the database connection details have been edited and the database created there are a number of things to alter in the database to make your Wordpress install work.

The most important changes are in the options table. There are two references to your URL in this table that must be altered to stop Wordpress redirecting back to your old site. This must be done via database access as Wordpress will redirect you when you try to login to the stie.

Changing the text of a submit button when clicked can be useful if you are writing an AJAX application or you know that there will be some sort of delay. Providing the user with some form of feedback is a useful way of letting them know they they have done something.

First, we need a form to work with, so I built a quick one here. Notice that the submit button has an onclick action associated with it, this will be used later to enable us to alter the text of the button.

If you want to create a "rounded" time stamp, for example, to the nearest 15 minutes use this as a reference:

Setting up a permalinks structure in Wordpress one of the things I normally do right after installing a blog, before event getting started on the templates. However, I always seem to forget what to put in the box so I thought I would put this here to remind myself and to go over the best practices on your own site in terms of SEO.

To set the permalinks on your Wordpress install go into Settings > Permalinks and enter the following into the Custom Structure field.

/%postname%-%post_id%.html

This will make a post on your site have a URL something like this.

/this-is-a-new-post-2.html

It is also possible to create a permalink using the category slug by using the %category% option.

/%category%/%postname%-%post_id%.html

So the post above would become the following.

Converting an IP address into some useful location information can be useful if you want to find out where sites are hosted or customise content to users depending on their location.

All this code is freely available over at github.

There are several ways to do this, all of which have their advantages and disadvantages, but sticking with one can cause rewriting a lot of code in the future. So rather than pick one and stick with it I decided to use dependency injection to allow different classes to be used that convert IP addresses to locations in different ways. The first task is to create an abstract class that will be used to construct the rest of the IP location classes. Each class that extends this abstract class will contain a method called getIpLocation() that will convert an IP address into a location, and a method that will update the data source for the location lookup. Rather than lump all of the classes into a single directory I have created a directory called Service, into which all of the different classes that lookup IP addresses will be kept.

Whilst setting up a new Wordpress install for a site development I found an odd little issue that would only occur in certain circumstances. My current development platform consists of an Apache server on which I create a virtual host for every development site I need. However, rather than setting a DNS entry for each address I just listen to diferent ports. In this particular instance I used the port 59419.

When the install was complete I was presented with the following error at the top of every admin page.