In PHP it is not required to initialize variables before their usage. However, using uninitialized variables is considered bad practice and should be avoided because of the following reasons:

Noncompliant Code Example

<?php

function getText(array $lines): string {
    foreach ($lines as $line) {
        $text .= $line;
    }

    return $text;
}

Compliant Solution

<?php

function getText(array $lines): string {
    $text = "";

    foreach ($lines as $line) {
        $text .= $line;
    }

    return $text;
}

See