Avoid Duplicate Code in PHP: The DRY Principle

DRY stands for Don’t Repeat Yourself. When the same logic exists in several places, a change must be made everywhere, and one copy is always forgotten.

Spot the repetition

index.php

PHP

<?php
// Page 1
$name1 = htmlspecialchars(trim("  Ana <b>  "), ENT_QUOTES, "UTF-8");
// Page 2
$name2 = htmlspecialchars(trim("  Ben & Co "), ENT_QUOTES, "UTF-8");
// Page 3 ... and so on

echo $name1 . " | " . $name2;

Output

OUTPUT

Ana &lt;b&gt; | Ben &amp; Co

The same two steps appear on every page. If you later decide to also limit the length, you must edit every copy.

Extract a function

index.php

PHP

<?php
function cleanName(string $text): string
{
    return htmlspecialchars(trim($text), ENT_QUOTES, "UTF-8");
}

echo cleanName("  Ana <b>  ") . " | " . cleanName("  Ben & Co ");

Output

OUTPUT

Ana &lt;b&gt; | Ben &amp; Co

Now the rule is in one place and has a name.

Extract a template

HTML repeats too. A product card that is copied for each product should be a template that you include with different data.

product-card.php

PHP

<article class="card">
  <h2><?= htmlspecialchars($product["name"]) ?></h2>
  <p><?= number_format($product["price"], 2) ?></p>
</article>

index.php

PHP

<?php
$products = [
    ["name" => "Pen", "price" => 12],
    ["name" => "Book", "price" => 250.5],
];

foreach ($products as $product) {
    include __DIR__ . "/product-card.php";
    echo "\n";   // a line break between the cards
}

Output

OUTPUT

<article class="card">
  <h2>Pen</h2>
  <p>12.00</p>
</article>
<article class="card">
  <h2>Book</h2>
  <p>250.50</p>
</article>

Use data, not copies of code

Repeated if branches that differ only in a value can often become a lookup array.

index.php

PHP

<?php
// Repetitive
function badgeBad(string $status): string
{
    if ($status === "paid") { return "green"; }
    if ($status === "pending") { return "orange"; }
    if ($status === "failed") { return "red"; }
    return "grey";
}

// DRY
function badge(string $status): string
{
    return ["paid" => "green", "pending" => "orange", "failed" => "red"][$status] ?? "grey";
}

echo badgeBad("pending") . " " . badge("pending");

Output

OUTPUT

orange orange

When not to be DRY

Do not merge code that looks alike but exists for different reasons. If two pieces will change independently, a shared function can create a knot: changing one breaks the other. A little duplication is better than the wrong abstraction.

A useful guideline: wait until you see the same thing three times, then extract it.

lightbulb

Name what you extract

A function called cleanName() or renderCard() says what it is for. A vague name like helper1() just moves the confusion.