isfile

Isfile is a common predicate name used in many programming languages and environments to test whether a given filesystem path designates a regular file. It typically returns true when the path exists and points to a file, and false for non-existent paths, directories, or other non-regular targets. Some implementations may also return false for certain special files such as devices or sockets, depending on their definitions.

Implementation and behavior vary by language, but most rely on filesystem metadata queries, often via a stat-like system call. A key variation is whether the check follows symbolic links. Some variants test the status of the path’s target (following links), while others test the link itself (not following). When following links is configurable, choosing the appropriate mode is important to avoid inadvertently validating a link to a non-regular target or encountering broken links.

Common language examples. In Python, the isfile predicate is exposed as os.path.isfile(path) or Path.is_file() and returns True for existing regular files. In PHP, is_file(string $filename) returns true if the filename exists and is a regular file, false for directories, non-existent paths, or non-regular targets. Other languages include analogous functions or methods, sometimes named differently but serving the same purpose. Shell environments often provide a test or [ command with the -f flag to perform a similar check.

Edge cases and usage. isfile-style checks are frequently used for input validation, file loading, and conditional processing based on the presence of a file. They may be affected by permissions, broken links, or the distinction between regular files and special file types. See also: isdir, exists, stat, lstat.