PHP filegroup Function
last modified April 3, 2025
The PHP filegroup function retrieves the group ownership of a file.
It returns the group ID (GID) of the file specified by the filename.
Basic Definition
The filegroup function returns the group ID of the specified file.
It takes one parameter: the filename path as a string.
Syntax: filegroup(string $filename): int|false. The function
returns the group ID on success, or false on failure.
Basic filegroup Example
This shows the simplest usage of filegroup to get a file's group ID.
<?php
declare(strict_types=1);
$filename = "/var/www/html/index.php";
$group_id = filegroup($filename);
if ($group_id !== false) {
echo "Group ID: " . $group_id;
} else {
echo "Could not retrieve group information";
}
This retrieves the group ID of "index.php". The result is numeric on Unix-like systems. Always check for false return value in case of errors.
Getting Group Name
We can use posix_getgrgid to convert the GID to a group name.
<?php
declare(strict_types=1);
$filename = "/etc/passwd";
$group_id = filegroup($filename);
if ($group_id !== false) {
$group_info = posix_getgrgid($group_id);
echo "Group name: " . $group_info['name'];
} else {
echo "Could not retrieve group information";
}
This example shows how to get the human-readable group name instead of just the
numeric ID. The posix_getgrgid function is required.
Checking File Permissions
We can combine filegroup with posix_getegid to check
if the current process has access to a file.
<?php
declare(strict_types=1);
$filename = "/var/log/syslog";
$file_group = filegroup($filename);
$current_group = posix_getegid();
if ($file_group !== false) {
if ($file_group === $current_group) {
echo "Current process has group access to the file";
} else {
echo "Current process does not have group access";
}
} else {
echo "Could not retrieve group information";
}
This checks if the current process runs under the same group as the file. This can help determine if group permissions would apply to file operations.
Error Handling
Proper error handling is important when working with filesystem functions.
<?php
declare(strict_types=1);
$filename = "/nonexistent/file.txt";
$group_id = filegroup($filename);
if ($group_id === false) {
$error = error_get_last();
echo "Error: " . $error['message'];
} else {
echo "Group ID: " . $group_id;
}
This demonstrates proper error handling when the file doesn't exist or isn't
accessible. The error_get_last function helps get error details.
Comparing Group Ownership
We can compare group ownership between two files using filegroup.
<?php
declare(strict_types=1);
$file1 = "/etc/passwd";
$file2 = "/etc/group";
$group1 = filegroup($file1);
$group2 = filegroup($file2);
if ($group1 !== false && $group2 !== false) {
if ($group1 === $group2) {
echo "Both files belong to the same group";
} else {
echo "Files have different group ownership";
}
} else {
echo "Could not retrieve group information for one or both files";
}
This example compares the group ownership of two system files. It's useful for checking consistency in file permissions across related files.
Best Practices
- Error Checking: Always check for false return values.
- Security: Be cautious with sensitive file operations.
- Performance: Cache results if checking repeatedly.
- Cross-platform: Note Windows may behave differently.
- Permissions: Ensure proper read permissions for files.
Source
This tutorial covered the PHP filegroup function with practical
examples showing its usage in different scenarios.