PHP is_link Function

last modified April 3, 2025

The PHP is_link function checks whether a filename is a symbolic link. It’s part of PHP’s filesystem functions and helps in file system operations.

Basic Definition

The is_link function returns true if the filename exists and is a symbolic link. It takes one parameter: the path to check.

Syntax: is_link(string $filename): bool. The function returns false for non-existent files or files that aren’t symbolic links.

Basic is_link Example

This shows the simplest usage of is_link to check a file.

basic_is_link.php

<?php

declare(strict_types=1);

$filename = “/path/to/symlink”;

if (is_link($filename)) { echo “$filename is a symbolic link”; } else { echo “$filename is not a symbolic link”; }

This checks if the given path is a symbolic link. The function returns a boolean that we can use in conditional statements.

Checking Before Reading Link

We often use is_link before calling readlink.

is_link_readlink.php

<?php

declare(strict_types=1);

$filename = “/path/to/symlink”;

if (is_link($filename)) { $target = readlink($filename); echo “Link points to: $target”; } else { echo “Not a symbolic link”; }

Here we safely check if the file is a link before trying to read its target. This prevents errors when calling readlink on non-links.

Checking Multiple Files

We can use is_link in a loop to check multiple files.

multiple_files.php

<?php

declare(strict_types=1);

$files = [“file1”, “file2”, “file3”];

foreach ($files as $file) { if (is_link($file)) { echo “$file is a symbolic link\n”; } }

This example checks each file in an array to see if it’s a symbolic link. The function works the same way when processing multiple files in sequence.

Combining with file_exists

We can combine is_link with file_exists for robust checks.

with_file_exists.php

<?php

declare(strict_types=1);

$filename = “/path/to/file”;

if (file_exists($filename)) { if (is_link($filename)) { echo “Exists and is a symbolic link”; } else { echo “Exists but not a symbolic link”; } } else { echo “File does not exist”; }

This checks file existence first, then determines if it’s a symbolic link. This approach prevents errors from checking non-existent files.

Real-world Directory Scan

Here’s how to use is_link when scanning a directory.

directory_scan.php

<?php

declare(strict_types=1);

$dir = “/path/to/directory”;

if ($handle = opendir($dir)) { while (false !== ($entry = readdir($handle))) { if ($entry != “.” && $entry != “..”) { $fullpath = $dir . “/” . $entry; if (is_link($fullpath)) { echo “$entry is a symbolic link\n”; } } } closedir($handle); }

This scans a directory and identifies all symbolic links. It shows how to use is_link in a real directory processing scenario.

Edge Cases

is_link has specific behaviors with certain edge cases.

edge_cases.php

<?php

declare(strict_types=1);

// Non-existent file var_dump(is_link("/nonexistent/file")); // bool(false)

// Regular file (not a link) touch("/tmp/regular_file"); var_dump(is_link("/tmp/regular_file")); // bool(false)

// Actual symbolic link symlink("/tmp/regular_file", “/tmp/symlink”); var_dump(is_link("/tmp/symlink")); // bool(true)

The function returns false for non-existent files and regular files. It only returns true for actual symbolic links that exist on the filesystem.

Best Practices

• Check existence: Combine with file_exists for robust code.

• Error handling: Handle cases where links might be broken.

• Permissions: Ensure proper permissions to check links.

• Cross-platform: Behavior may vary on different OS.

• Performance: Cache results if checking repeatedly.

Source

PHP is_link Documentation

This tutorial covered the PHP is_link 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.

List all PHP Filesystem functions.