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file(1)
NAME
  file - Determines file type

SYNOPSIS
  file [-c] [-f file_list] [-m magic_file] file...

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  file:	 XPG4, XPG4-UNIX

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

OPTIONS
  -c  [DIGITAL]	 Checks the magic file (/etc/magic by default) for format
      errors.  This validation is not normally done.  File typing is not done
      under this option.

  -f file_list
      [DIGITAL]	 Reads file_list for a list of files to examine.

  -m magic_file
      [DIGITAL]	 Specifies magic_file as the magic file (/etc/magic by
      default).

OPERANDS
  file
      The path name of the file to be tested.

DESCRIPTION
  The file command reads input files and performs a series of tests on each
  one. It then attempts to classify them by type and writes the file types to
  standard output.

  The file command uses the /etc/magic file to identify files that have some
  sort of a magic number (that is, any file containing a numeric or string
  constant that indicates its type).

  [DIGITAL]  If a file appears to be plain text, file examines the first 512
  bytes and tries to determine what kind of text it is.	 If the first 512
  bytes only contain ASCII characters, file returns either ASCII text or
  English text.	 If the file contains other characters (that is, European or
  Asian extended characters), file returns data.


  [DIGITAL]  If a file does not appear to be plain text, file attempts to
  distinguish a binary data file from a text file that contains extended
  characters.  If the file is an a.out file and the version number is greater
  than zero, file displays the version stamp.


  [DIGITAL]  For character special files, part of the identification is
  information about the devices the system shows as active. In particular,
  file returns device-specific information such as controller type and unit,
  device type and unit, and status (offline, write locked, density, errors).
  The general categories currently implemented are disk, tape, and terminal
  devices. The supported terminal devices include Local Area Terminals (LAT)
  but not Local Area Network (LAN) pseudo-terminals.

  [DIGITAL]  The following example shows how the file command identifies a
  device. The output is shown on two lines due to space considerations, but
  appears on one line on a display.

	% file /dev/rrz0c

	/dev/rrz0c: character special (8/2) SCSI #0
	RZ24 disk #0 (SCSI ID #0)

  [DIGITAL]  On DIGITAL UNIX systems, the file command recognizes OSF core
  files.  For example:

       % file core

	 core:	 core dump, generated from 'mwm'

  [DIGITAL]  The amount and type of information the file command returns can
  depend on the permissions of the file being queried. For example, most
  special device files have permissions that allow access only by root and
  non-root users cannot open them. The file command has to open the device
  and only root has the proper permissions.  Thus, if the file command is
  issued by a non-root user, it can report only information it can determine
  without gaining access to the device.

  [DIGITAL]  The file command also uses internal tables to decode certain
  types of files. The following example shows the keywords the file command
  uses to locate troff, C code, and assembler code.

       char  *troff[] = {    /* new troff intermediate lang */
	     "x","T","res","init","font","202","V0","p1",0};
       char  *c[] = {
	     "int","char","float","double","struct","extern",0};
       char  *as[] = {
	     "globl","byte","align","text","data","comm",0};

  The file types recognized and identification displayed include those shown
  in the following table:

  ____________________________________________________________
  If file is a				  It is identified as
  ____________________________________________________________
  directory				  directory
  FIFO					  fifo
  block special				  block special
  character special			  character special
  executable binary			  executable
  empty regular file			  empty
					  archive

  ar archive library (see ar)
					  cpio archive

  extended cpio format (see pax)
					  tar archive

  extended tar format (see tar)
  shell script				  commands text
  C-language source			  c program text
  FORTRAN source			  fortran program text
  ____________________________________________________________





RESTRICTIONS
  [DIGITAL]  The file command often does a poor job of distinguishing C
  programs, shell scripts, English text, and ASCII text.  In addition, it
  does not recognize certain programming languages, including Modula, Pascal,
  and Lisp.

EXIT STATUS
  The following exit values are returned:

  0   Successful completion.

  >0  An error occurred.

EXAMPLES
   1.  To display the type of information a file contains, enter:
	    file myfile

       This displays the file type of myfile (directory, data, ASCII text, C
       program source, archive, and so on).

   2.  To display the type of each file named in a list of file names, enter:
	    file -f filenames

       This displays the type of each file with a name that appears in
       filenames.  Each file name must appear alone on a line.

       To create filenames, enter:
	    ls > filenames

       Then edit filenames as desired.

FILES
  /etc/magic
      File type database

SEE ALSO
  Commands:  r(1), cpio(1), ls(1), pax(1), tar(1)

  Files:  magic(4)

  Standards:  standards(5)

  Programmer's Guide