Txp:Variable Uncovered

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As of version 4.0.7, Textpattern has a few new strings to its bow. One of these is the concept of economical storage and retrieval via <txp:variable /> but for those without a coding mindset it can appear tricky at first.

We caught up with this new tag We caught up with this new tag… and asked it to keep things simple for onceas it was preparing to bamboozle some more innocent people and asked it to keep things simple for once.

TXPQ What is life all about?

txp:variable Being flexible, inventive and useful.

TXPQ Tell us about your childhood.

txp:variable Since I was born my parents brought me up to make the most of what I’ve got. I was a little sensitive about my weight — just 10 lines of code — but they told me bedtime stories about how I’d change the way people use Textpattern. Above all, they taught me that with my in-built flexibility, I could provide site designers with a little programming ability without the need for PHP.

TXPQ But programmers are strange creatures; should we be worried that TXP is turning into a geeks-only tool instead of for designers?

txp:variable lol, not at all. I can appeal to designers as well as codersIf you can’t see a use for me right away, that’s fine. I’m there as a convenience if you ever need me. And I’m sure I can appeal to designers as well as coders if you give me a few minutes. I don’t bite.

TXPQ OK, ummm, so convince us. Ease us into your mindset.

Save it for Later

txp:variable I’m all about storage and retrieval and keeping pages fairly lean by avoiding duplication. One of the simplest things you can do is store a single value you use again and again across your pages.

For example, if you use the same URL a few times, instead of hard-coding it into all your forms or pages, you can define it once and refer to it; a bit like adding a URL to the bottom of an article and referring to it many times with Textile.

Doing things this way means that if you ever need to change the URL in future you can do it in one place and it gets changed everywhere. Perhaps in a form called constants:

<txp:variable name="megablog"
  value="<a href='http://my.megablog.com/is/here'>MegaBlog</a>" />

<txp:variable name="coderblog"
  value="<a href='http://blogs.com/~foo/coder'>Coding blog</a>" />

If you use <txp:output_form form="constants" /> at the top of your page template, the two variables called megablog and coderblog then become available to be used freely wherever you like; even in articles!

To retrieve the value at any time you would write:

Don’t forget to visit my <txp:variable name="megablog" /> to learn about how cool I am.

You could even assign the <txp:variable /> as a QuickTag if you use it often enough.

Ch-ch-ch-Changes

TXPQ So once a value is set, is that it?

txp:variable Not at all. You can set and reset any value as often as you like during the course of the pageYou can set and reset any value as often as you like during the course of the page. Let’s run through an example, step by step:

<txp:variable name="where_are_we" value="A page" />

Initially the value of the variable named "where_are_we" is set to "A page". If nothing is done to alter that variable from now on, it will stay this way. But:

<txp:if_search>

  <!-- This conditional section is only entered
    if the visitor is using the search feature -->

  <txp:variable name="where_are_we"
          value="We're in a search" />

</txp:if_search>

If a search is in progress, the variable named "where_are_we" now has its value changed to "We're in a search". If, however, a search is not in progress, at this point the variable’s value would still be "A page".

Adding:

<txp:if_category>

  <!-- This conditional section is only entered
    if the visitor is browsing by category -->

  <txp:variable name="where_are_we"
          value="I lied, it's a category list" />

</txp:if_category>

means that — similarly to above — "where_are_we" is only altered if the visitor is browsing a category. If they were not browsing a category, the value would be left as it was (which is either "We're in a search" if the visitor was searching for something, or "A page" if they weren’t).

So if the above I have set and subsequently changed the value depending on what the visitor is doingthree chunks of code are put together I have set and subsequently changed the value depending on what the visitor is doing. At some point later you can print out my latest value with:

<txp:variable name="where_are_we" />

The result of that statement would display one of the following:

TXPQ Seems simple enough. What’s the next step?

Parse the Sauce

txp:variable With the new tag parser in TXP 4.0.7 I can be used inside other tags to pass values into them:

<txp:if_section name="gallery">

  <txp:variable name="category_type" value="image" />

<txp:else />

  <txp:variable name="category_type" value="article" />

</txp:if_section>

<txp:category_list type='<txp:variable name="category_type" />' />

That’s very useful, since repeating the <txp:category_list /> tag and, potentially, all its other attributes inside both branches of the <txp:if_section /> clutters the form and is a pain to update. I can be used to simplify page structure and help make sure you only have to refer to stuff onceSo I can be used to simplify page structure and help make sure you only have to refer to stuff once.

One thing to note: the single quotes around me when inserted inside another tag tell the parser to go ahead and parse me, putting the result inside the type attribute. If the tag had been written like this instead:

<txp:category_list type="<txp:variable name="category_type" />" />

it may have worked in this simple example but other times it might not. The rule of thumb is: if you want to put a tag as an attribute, surround the contents of the attribute in single quotes.

TXPQ It’s starting to make sense at last! You could be used the other way round, I assume? Other tags can be put inside you?

txp:variable Of course. But on my own that may not be incredibly helpful since all tags can take other tags directly now. Perhaps this is a good time to introduce my brother.

Family Values

TXPQ A sibling?

txp:variable Yep. Meet <txp:if_variable />. He can look at anything I have stored and test it, so action can be taken based on what value is stored.

TXPQ Like a kind of generic <txp:if /> ?

txp:variable Exactly.

My brother is check for the existence of a variable — that is, a variable that has been defined earlier in the pagevery quiet and unassuming in daily life but rather powerful when poked; a bit like Wolverine. Firstly, he can check for the existence of a variable — that is, a variable that has been defined earlier in the page and may or may not have a value:

<txp:variable name="test_me" value="" />

<txp:variable name="test_me_too" value="Something in here" />

<txp:if_variable name="test_me">
  <p>Yes, I exist, even though I don't have a value</p>
</txp:if_variable>

<txp:if_variable name="test_me_too">
  <p>I exist as well! And I have a value</p>
</txp:if_variable>

In both cases above, the value inside the <txp:if_variable /> statement will be displayed.

Adding value="" can test for the existence of an empty variable, which is quite useful when the value you assign to the variable is the result of another tag. That means you could assign the output of <txp:keywords /> to a variable and then take different action depending if there were any keywords returned or not. So essentially you can create a brand new tag – <txp:if_keywords />!

TXPQ So let me get this right. Can I do this using your example above?

<txp:variable name="has_keywords" value='<txp:keywords />' /> 

<txp:if_variable name="has_keywords" value="">

  <p>Article keywords: <txp:keywords /></p>

<txp:else />

  <p>No keywords listed for this article</p>

</txp:if_variable>

[ EDITED to add value="" , thanks maniqui / Els / wet ]

I just I just created a new tag? Wow!created a new tag? Wow!

txp:variable More or less, yes. Cool huh?

TXPQ Very.

All Things Equal

TXPQ So he’s your brother but he certainly ain’t heavy — just 15 lines of source code! You said he can help in two ways…

txp:variable That’s right. The other way is to test if a particular variable matches a given value. For example, the <txp:if_author /> tag only works within search criteria, but what if you wanted to take some action on every page based on who authored an article?

You could do this somewhere near the top of your page template:

<txp:variable name="this_author" value='<txp:author />' />

Which would assign the current author to the variable labelled this_author. Then, sometime later in your page template you could put:

<txp:if_variable name="this_author" value="peter">

  <txp:css n="a_different_style" />

<txp:else />

  <txp:css />

</txp:if_variable>

apply alternating colours without plugins, thus keeping your pages nimble and your plugin count downSo any articles written by Peter use a different stylesheet. You could apply this to comments to more easily highlight author comments or apply alternating colours without plugins, thus keeping your pages nimble and your plugin count down.

TXPQ Hey that’s neat. So what else can you do?

And There’s More

txp:variable Plenty. There are some esoteric uses over on the forums.

We can really be of value for applying little graphical or typographical niceties such as those examples, or for radically simplifying the page structure to keep your pages trim, lean and light in the true spirit of Textpattern. And of course everything in between.

TXPQ Excellent! Thank you for opening our eyes to the possibilities. We wish you much variable goodness in years to come.

txp:variable :

<txp:variable name="sayonara" value="Thanks. You're welcome!" />

<txp:if_variable name="interview" value="over">

  <txp:variable name="sayonara" />

</txp:if_variable>

:-)

If you have found any cool uses for me and my brother, post a comment about it and let us know.

Author: Stef Dawson