PHP is_readable() Function: Syntax, Usage, Example, and Important Considerations

PHP function is_readable() is used to check whether a specified file is readable. It accepts a file path as a parameter and returns a boolean indicating if the file can be read.

Using is_readable() you can verify that a file exists and has read permission before attempting to read it, which helps avoid unexpected errors during file operations.

Basic Syntax:

bool is_readable ( string $filename )

The parameter $filename is the file path to check; it can be relative or absolute. The function returns true if the file is readable, otherwise false.

Example Code:

$file = 'path/to/file.txt';
if (is_readable($file)) {
    echo "文件可读取";
} else {
    echo "文件不可读取";
}

In the example we first define a file path $file, then use is_readable() to check if the file can be read. If it is readable, the script outputs "文件可读取"; otherwise it outputs "文件不可读取".

Notes:

is_readable()

can only check files, not directories.

If the file does not exist or cannot be accessed, is_readable() returns false.

The function is sensitive to the permission context of the PHP runtime user; even if the file has read permission, the function will return false if the PHP process lacks the necessary rights.

Error Handling:

If the argument passed to is_readable() is not a string, PHP will emit an E_WARNING level error.

If the file path is excessively long or contains illegal characters, is_readable() may return false.

Summary:

The is_readable() function is a useful tool for checking file readability before attempting to read a file, helping to prevent unexpected errors. When using it, ensure the file path is correct and be aware of the PHP process's permission context.

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