Building Strings with Dots and Variables

PHP gives you the means to build dynamic strings. You can run a function and then append a string literal to the end of it. You can embed a variable into a string. You can append the value of the variable to another string. You see it in the themes and plugins, as well as WordPress Core. Let’s talk about it.

With the PHP concatenation operator, i.e. . (dot), you are able to smoosh two string values together to make a new string. For example, look at this code:

include_once( get_template_directory() . '/lib/init.php' );

What is the above code doing? It’s loading a file using include_once(). The file’s full path on the hard drive is dynamically built at runtime. The root to the theme’s directory (this is the parent theme) is fetched using the WordPress function get_template_directory(). Then using the dot the file’s path and filename within the theme is appended to the end of the first part. That new string is passed into the include, which then locates and loads the file into memory.

Look at your theme. Find one of the file loaders. You’ll see this technique being used. It’s prevalent in WordPress.

In this episode, you’ll use the following code to test and see how this works. I’ll walk you through it step-by-step and see the values as well as the sequence of how the string is put together.

Need the code used in this video? Click here to get it

The following code is broken up into the 3 sessions covered in this episode. When you do each session, comment out each session above it using // before each line of code.

	<?php
	// Session 1
	d( get_template_directory() );
	ddd( get_template_directory() . '/lib/init.php' );
	// Session 2
	d( $parent_theme_directory );
	ddd( $parent_theme_directory . '/lib/init.php' );
	// Session 3
	$suffix = ( defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ) ? '' : '.min';
	d( get_stylesheet_directory_uri() );
	d( $suffix );
	d( '/js/responsive-menus{$suffix}.js' );
	d( "/js/responsive-menus{$suffix}.js" );
	ddd( get_stylesheet_directory_uri() . "/js/responsive-menus{$suffix}.js" );

view raw

building-strings.php

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Then you’ll learn about embedding variables within a string and its syntax. PHP lets you embed a variable with the following syntax:

• The string must be wrapped in a double quote (not single).
• Place the variable where you want it to appear within the single.
• Wrap the variable in curly braces

For example,

$suffix = ( defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ) ? '' : '.min';
d( get_stylesheet_directory_uri() . "/js/responsive-menus{$suffix}.js" );

Look at the syntax of the string on the second line. It starts with a double quote, then has a string literal, then an opening curly brace, then the variable, closed by the curly brace, etc. When this code runs, the value bound to that variable will be inserted into the string.

Want to learn more about the ternary operator? Click here to watch this quick tip.

Challenge Yourself

$file = '/js/responsive-menus{$suffix}.js';

For the above code, if the suffix is an empty string, what is the value of $file when this code runs? Why?

/js/responsive-menus{$suffix}.js

Why? Single quotes were used. Therefore, the variable is read by PHP as just part of the string, i.e. it’s just characters. In order for PHP to replace the variable with its value, you must use double quotes.

$theme_directory = get_stylesheet_directory();
$file_in_theme   = '/lib/theme-defaults.php';

include( $theme_directory . $file_in_theme );

include( get_stylesheet_directory() . '/lib/theme-defaults.php' );

True or False. Using the above code, the theme-defaults.php file is only loaded once.

False.

Why? The variables are holding each part of the file’s location. Therefore,

$theme_directory . $file_in_theme

will become the same string as

get_stylesheet_directory() . '/lib/theme-defaults.php'.

They are the same value and equal. Then the code uses include. That means the file can be loaded more than once. Each include in this example is loading the exact same file. Therefore, the file is being loaded two times.

$current_user = wp_get_current_user();
$first_name   = $current_user->user_firstname;
$message      = "Hello and Welcome, {$first_name}";

For the above code, what is the value of the message if the user is Sally Jones?

Hello and Welcome, Sally.

The function wp_get_current_user() get the current user’s information and returns an object (don’t worry about understanding objects right now). Then one of the pieces of information on that object is the user’s first name. When that is embedded into the string, the message will include her name.