PHP linkinfo Function

last modified April 3, 2025

The PHP linkinfo function retrieves information about a link. It returns the st_dev field of the Unix C stat structure for the link.

Basic Definition

The linkinfo function checks if a path is a link and returns information about it. It returns 0 or false if the link doesn't exist.

Syntax: linkinfo(string $path): int|false. The function is useful for verifying symlinks before operations. It works only on Unix-like systems.

Basic linkinfo Example

This shows the simplest usage of linkinfo to check a symlink.

basic_linkinfo.php

<?php

declare(strict_types=1);

$path = "/usr/bin/php";
$linkInfo = linkinfo($path);

if ($linkInfo !== false) {
    echo "Link exists with device ID: " . $linkInfo;
} else {
    echo "Not a link or doesn't exist";
}

This checks if "/usr/bin/php" is a symlink. If it is, it returns the device ID. The function returns false for regular files or non-existent paths.

Checking Symlink Validity

We can use linkinfo to verify if a symlink points to a valid target.

check_symlink.php

<?php

declare(strict_types=1);

$symlink = "/tmp/mysymlink";

if (linkinfo($symlink) {
    echo "Symlink exists and is valid";
} else {
    echo "Symlink is broken or doesn't exist";
}

This example checks the validity of a symlink. A return value greater than 0 indicates a valid symlink. Broken links return false.

Comparing Link Information

linkinfo can compare if two paths are on the same filesystem device.

compare_links.php

<?php

declare(strict_types=1);

$link1 = "/usr/bin/php";
$link2 = "/usr/local/bin/php";

$info1 = linkinfo($link1);
$info2 = linkinfo($link2);

if ($info1 === $info2) {
    echo "Links are on the same device";
} else {
    echo "Links are on different devices";
}

This compares device IDs of two links. Matching IDs mean they're on the same device. Different IDs indicate separate filesystems.

Error Handling

Proper error handling is important when working with linkinfo.

error_handling.php

<?php

declare(strict_types=1);

$path = "/nonexistent/link";

try {
    $result = linkinfo($path);
    
    if ($result === false) {
        throw new RuntimeException("Invalid link or path");
    }
    
    echo "Link device ID: " . $result;
} catch (Throwable $e) {
    echo "Error: " . $e->getMessage();
}

This demonstrates proper error handling. The try-catch block captures any filesystem-related errors. We also check for false returns explicitly.

Windows Compatibility Note

linkinfo has limited functionality on Windows systems.

windows_check.php

<?php

declare(strict_types=1);

$path = "C:\\Windows\\System32\\cmd.exe";

if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
    echo "linkinfo has limited functionality on Windows";
} else {
    $info = linkinfo($path);
    echo "Link info: " . ($info !== false ? $info : "Not a link");
}

On Windows, linkinfo only checks if the path exists. It doesn't provide device information. Always check the OS before using this function.

Best Practices

Check OS: Verify Unix-like system before use.
Error Handling: Always check for false returns.
Permissions: Ensure proper filesystem permissions.
Validation: Validate paths before processing.
Alternatives: Consider is_link() for simple checks.

Source

PHP linkinfo Documentation

This tutorial covered the PHP linkinfo function with practical examples showing its usage in different scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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