How to Insert a Variable Into a String in PHP

Master variable interpolation and concatenation, the two ways to add a variable to a string in PHP, and learn when to use each.

Published Categorized as PHP

If you want to include a variable in a string within your PHP code, there are a few ways to do it.

Here are two of my favorite approaches.

Variable Interpolation

Did you know that PHP allows you to *directly* include variables within double-quoted strings?

That’s right—there’s no need to concatenate strings or include any special characters. Literally all you have to do is to make sure you’re using double quotes.

This is known as variable interpolation, and here’s how it works:

$name = "John Doe";
echo "Hello, $name!"; // Output: Hello, John Doe!

With variable interpolation, you can place the variable right inside the string using the dollar sign ($) and curly braces ({}) if needed. It’s a concise way to incorporate variables into strings.

When to Use $variable, And When to Use {$variable}

Curly braces are used in variable interpolation within PHP strings to disambiguate variable names, access array elements or object properties, and handle complex expressions.

They provide clarity and help the interpreter accurately evaluate the intended variable or expression.

Here are a few scenarios where curly braces can be helpful.

Variable with complex name:

If your variable name has characters that could cause ambiguity for the PHP interpreter or for other developers looking at your code, using curly braces clarifies the variable you want to interpolate. For example:

$user = "John Doe";
echo "This is {$user}'s account."; // Output: This is John Doe's account.

Array elements or object properties:

When you want to access an element of an array or a property of an object within a string, curly braces are necessary. For example:

$person = ['name' => 'John Doe', 'age' => 30];
echo "Name: {$person['name']}, Age: {$person['age']}"; // Output: Name: John Doe, Age: 30

Here, the curly braces, which encapsulate square braces, help distinguish the array keys ('name' and 'age') from the surrounding text.

Complex expressions:

If you have complex expressions involving operators, functions, or calculations, you can enclose them in curly braces to ensure correct evaluation. For example:

$num1 = 5;
$num2 = 5;
echo "The sum is: {$num1 + $num2}"; // Output: The sum is: 10

In the example above, by enclosing the expression {$num1 + $num2} within curly braces, you ensure that the addition operation is performed correctly.

String Concatenation

You can concatenate (or, in English, join) the variable with the string using the dot (.) operator.

For example:

$name = "John Doe";
echo "Hello, " . $name . "!"; // Output: Hello, John Doe!

How to Choose

When choosing between one approach and the other for achieving a given task in programming, it’s helpful to consider:

  • Performance and computational efficiency
  • Readability and maintainability of your source code

Performance And Computational Efficiency

In terms of performance and computational efficiency, concatenation (using the dot operator) is generally more performant and economical compared to variable interpolation (using curly braces) in PHP.

The reason behind this is related to how PHP handles string concatenation and variable interpolation.

When you use concatenation, PHP combines separate string literals and variables into a single string.

This process is efficient because string concatenation is a simple operation that requires minimal computational overhead. Each string is concatenated directly without any additional parsing or interpretation.

On the other hand, variable interpolation involves parsing the string and identifying variables within it. PHP needs to scan the string for variables, evaluate their values, and then substitute them into the string.

This extra parsing and evaluation step can introduce additional computational overhead, especially if you have complex expressions or a large number of variables within the string.

That said, it’s important to note that the performance difference between concatenation and interpolation is typically negligible unless you’re dealing with extremely large strings or performance-critical code.

Readability and Maintainability

In most cases, the readability and maintainability of your code should take precedence over minor performance optimizations.

Whichever approach is the easier to read and maintain—and aligned to your team’s and/or organization’s coding style guide—is typically the one to opt for.

By Dim Nikov

Editor of Maker's Aid. Part programmer, part marketer. Making things on the web and helping others do the same since the 2000s. Yes, I had Friendster and Myspace.

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