Unix file types

The seven standard Unix file types are regular, directory, symbolic link, FIFO special, block special, character special, and socket as defined by POSIX.^[1] Different OS-specific implementations allow more types than what POSIX requires (e.g. Solaris doors). A file's type can be identified by the ls -l command, which displays the type in the first character of the file-system permissions field.

For regular files, Unix does not impose or provide any internal file structure; therefore, their structure and interpretation is entirely dependent on the software using them.^[2] However, the file command can usually be used to determine what type of data they contain.^[3]