The widespread use of databases has not deprived the ordinary file system of value. Writing and reading files still occupy a significant place in programming.
Algorithms for checking the availability of a file allow you to avoid errors when executing code. The PHP function file_exists offers a simple solution to verify the existence of a file or directory.
Syntax and use of the file_exists function
The result of the function is true or false. The only parameter is the file name and path to it. The result of the function is cached because if PHP file_exists does not work, and the file actually exists, then this is an algorithm error.
When using the clearstatcache () function, many errors can be avoided in examining the state of an accessible file system. But it should be borne in mind that on a nonexistent PHP file, file_exists will return false until the searched file is created, and then will return true even when it has already been deleted.
The correct combination of the clearstatcache () function and functions related to the file system (for example, is_writable (), is_readable (), is_executable (), is_file (), is_dir () and others) avoids "hidden" script execution errors.
Caching significantly improves system performance, but in some cases it can create really false results on important files and cause a serious, hard to detect execution error.
PHP function parameter file_exists
PHP can be installed on various computing platforms, and therefore, the naming of paths and files can be different.
The documentation declares that when checking PHP focuses on UID / GID, and not on effective identifiers. When developing an algorithm for using PHP file_exists, one should pay attention not only to the correct slashes (forward or reverse), the encoding of the file path and the name of the file itself, but also to check for the presence of the necessary register, correct characters, access rights, and other circumstances.
A negative result may be affected by the encoding of the script file; conversion of the character string obtained from the database may be required.
Putting the function into practice
The scope of PHP scripts is significantly different. This is not to say that PHP file_exists is used exclusively for storing system information, data files, objects, or dynamically generated images.
Cases of using streaming formation of large volumes of temporary information that are not efficiently immediately put into the database are frequent. Information from different visitors can flock to the site, and only after preliminary processing for a certain period of time, the necessary information should be placed in the database tables.
Reading system files can cause caching for multiple page refresh or incorrect visitor actions. There are a lot of situations in reality, but with the correct use of the function, it allows you to write safe and reliable code.