How to Differentiate Single and Double Quotes in PHP

1. Introduction to Single and Double Quotes in PHP
2. Differences Between Single Quote and Double Quotes During the Interpolation of String and Variable in PHP
3. Differences Between Single Quote and Double Quotes While Escaping Apostrophe in PHP

This article will introduce the differences between single and double quotes in PHP.

Introduction to Single and Double Quotes in PHP

In PHP, we use quotes to specify the value is a string literal. There are two different types of quotes. They are the single quote, ' and the double " quotes. However, we can specify the string literals using string syntaxes like herdoc and nowdoc. In this article, we will focus on the quotes. We can wrap the string literals with single or double quotes to represent the value as a string. An example is shown below.

Example Code:

<?php

echo "hey you \n";
echo 'hey you';

?>

Output:

hey you
hey you

In the example above, the use of both quotes seems to be the same. But that is not only the case. The function of the quotes are the same, but there is a difference in the way they work. We will discuss the significant differences between the single and double quotes below.

Differences Between Single Quote and Double Quotes During the Interpolation of String and Variable in PHP

The most significant difference between the single and the double quotes lies when we interpolate the string and the variable. The single quote does not interpolate the string and the variables. The content inside the single quote prints out as exactly as it is. In most cases, there is no compilation of any variables or escape sequences inside the single quote.

But, in the case of the double quote, the variable written inside the quotes will be interpolated with the string. It means that the variable in the string will be evaluated. Consequently, it is easy to use double quotes when interpolating the string and the variables. The advantage of double quotes over single quotes is that we need not concatenate the string and the variables using the . operator. However, as the variables need to be evaluated in the string, using double quotes will be slightly slower than using the single quote.

For example, create a variable $name and write the string Bond to it. Next, write the string The name is $name. and enclose the string with double-quotes. Use the echo function to print the string. Similarly, enclose the exact string with a single quote in the following line.

Example Code:

<?php

$name = "Bond";
echo "The name is $name. \n";
echo 'The name is $name.'; 

?>

Output:

The name is Bond.
The name is $name.

As the output shows, the variable $name is evaluated using double quotes. While using the single quote, the string is printed the way it is. This is one of the significant differences between the single and double quotes in PHP.

Differences Between Single Quote and Double Quotes While Escaping Apostrophe in PHP

This section will discuss the escape sequences using double quotes and single quotes in PHP. The escape sequences can be used inside the double quotes to escape the characters. Meanwhile, most escape sequences are not interpreted inside a single quote. However, there is an exception for escaping the apostrophe.

There is no need to escape the apostrophe if we write an apostrophe in the string while using double-quotes. But, in the case of a single quote, we need to escape it using \'. The example is shown below.

Example Code:

<?php

echo "Napoleon Hill's \"Think and grow rich\". \n";
echo 'Napoleon Hill\'s \"Think and grow rich\".';

?>

Output:

Napoleon Hill's "Think and grow rich".
Napoleon Hill's \"Think and grow rich\".

In the above code, it is obvious that the apostrophe must not escape using the double-quotes. The double quotes are also escaped inside the double quotes using the character escapes. Meanwhile, in the case of the single quote, the apostrophe is escaped using the character escape. In the latter case, the double quotes are not escaped while using the character escapes.

These are the significant differences between the single and double quotes in PHP.