The Uinx Programming Environment

The file system...in Open Source... What is in a file?..... the format of a file is determined by the programs that use it; there is a wide variety of file types, perhaps because there is a wide variety of programs. But since file types are not determined by the file system, the kernel can not tell you the type of a file: it does not know it. The file command makes an educated guess:

                              $file /bin/bin/ed  /usr/src/cmd/ed.c  /usr/man/man1/ed.1
                             /bin                                       : directory.
                             /bin/ed                                  : pure executable.
                            /usr/src/cmd/ed.c                : c program text.
                            /usr/man/man1/ed.1           : roff , nroff, or eqn input text.
                            $
THE UNIX PROGRAMMING ENVIRONMENT  by    BRAIN W.KERNIGHAN