PHP is_writeable Function
last modified April 3, 2025
The PHP is_writeable function checks whether a file or directory
is writable. It's essential for file operations to verify permissions first.
Basic Definition
The is_writeable function checks if the specified path exists and
is writable. It returns true if writable, false otherwise.
Syntax: is_writeable(string $filename): bool. Note that
is_writable is an alias with identical functionality. The function
considers both file permissions and filesystem restrictions.
Basic is_writeable Example
This shows the simplest usage of is_writeable to check a file.
<?php
declare(strict_types=1);
$file = "data.txt";
if (is_writeable($file)) {
echo "The file is writable";
} else {
echo "The file is not writable";
}
This checks if "data.txt" exists and is writable. The result depends on your filesystem permissions. Always check before attempting file operations.
Checking Directory Write Permissions
is_writeable can also check directory permissions.
<?php
declare(strict_types=1);
$dir = "/var/www/uploads";
if (is_writeable($dir)) {
echo "Directory is writable";
} else {
echo "Cannot write to directory";
}
This verifies if the web server can write to the uploads directory. Directory write permission is needed to create or modify files within it.
Using is_writeable Before File Operations
A practical example checking permissions before writing to a file.
<?php
declare(strict_types=1);
$logFile = "application.log";
if (!is_writeable($logFile) && file_exists($logFile)) {
die("Log file exists but isn't writable");
}
$result = file_put_contents($logFile, "New log entry\n", FILE_APPEND);
if ($result === false) {
die("Failed to write to log file");
}
echo "Log entry added successfully";
This demonstrates proper error handling when writing to files. We check writeability before attempting the operation to prevent runtime errors.
Checking Multiple Files
You can check write permissions for multiple files in one operation.
<?php
declare(strict_types=1);
$files = ["config.ini", "cache/data.cache", "templates/default.html"];
foreach ($files as $file) {
echo $file . ": " . (is_writeable($file) ? "Writable" : "Not writable") . "\n";
}
This loops through an array of files and reports their write status. Useful for verifying all required files are accessible before application startup.
Real-world Configuration Check
A more complex example checking configuration file permissions.
<?php
declare(strict_types=1);
function checkConfigFile(string $path): void {
if (!file_exists($path)) {
if (!is_writeable(dirname($path))) {
throw new RuntimeException("Config directory not writable");
}
return;
}
if (!is_writeable($path)) {
throw new RuntimeException("Config file exists but isn't writable");
}
}
checkConfigFile("/etc/myapp/config.ini");
echo "Configuration file check passed";
This function checks if either the config file is writable or its directory is writable if the file doesn't exist yet. Demonstrates comprehensive permission checking for configuration management.
Edge Cases
is_writeable has some behaviors worth noting in edge cases.
<?php
declare(strict_types=1);
// Non-existent file
var_dump(is_writeable("nonexistent.txt")); // bool(false)
// Symbolic link
symlink("data.txt", "link.txt");
var_dump(is_writeable("link.txt")); // Depends on target permissions
// Windows share
var_dump(is_writeable("\\\\server\\share\\file.txt")); // Checks network permissions
For non-existent files, returns false. For symlinks, checks the target file. Windows network paths are supported but subject to additional permission layers.
Best Practices
- Check Early: Verify permissions as soon as possible.
- Error Handling: Provide clear error messages when checks fail.
- Security: Don't expose sensitive permission details to users.
- Race Conditions: Be aware permissions may change between check and use.
- Alternatives: Consider try/catch for actual operations instead of just checks.
Source
PHP is_writeable Documentation
This tutorial covered the PHP is_writeable function with practical
examples showing its usage in different scenarios.