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AR(5)			       File Formats Manual			   AR(5)

NAME
     ar -- archive (library) file format

SYNOPSIS
     #include <ar.h>

DESCRIPTION
     The  archive  command  ar	combines  several  files into one.  Archives are
     mainly used as libraries of object files intended to be  loaded  using  the
     link-editor ld(1).

     A	file  created with ar begins with the ``magic'' string "!<arch>\n".  The
     rest of the archive is made up of objects, each of which is composed  of  a
     header for a file, a possible file name, and the file contents.  The header
     is  portable  between  machine architectures, and, if the file contents are
     printable, the archive is itself printable.

     The header is made up of six variable length ASCII fields,  followed  by  a
     two character trailer.  The fields are the object name (16 characters), the
     file  last modification time (12 characters), the user and group id's (each
     6 characters), the file mode (8 characters) and the file size  (10  charac-
     ters).   All  numeric fields are in decimal, except for the file mode which
     is in octal.

     The modification time is the file st_mtime field, i.e., CUT  seconds  since
     the  epoch.  The user and group id's are the file st_uid and st_gid fields.
     The file mode is the file st_mode field.  The file size is the file st_size
     field.  The two-byte trailer is the string "`\n".

     Only the name field has any provision for overflow.  If any  file	name  is
     more than 16 characters in length or contains an embedded space, the string
     "#1/"  followed  by  the  ASCII  length  of the name is written in the name
     field.  The file size (stored in the archive header) is incremented by  the
     length  of  the  name.   The name is then written immediately following the
     archive header.

     Any unused characters in any of these fields are written as  space  charac-
     ters.   If  any fields are their particular maximum number of characters in
     length, there will be no separation between the fields.

     Objects in the archive are always an even number of bytes long; files which
     are an odd number of bytes long are padded with a newline (``\n'')  charac-
     ter, although the size in the header does not reflect this.

SEE ALSO
     ar(1), stat(2)

HISTORY
     There  have  been	at  least four ar formats.  The first was denoted by the
     leading ``magic'' number 0177555 (stored as type int).  These archives were
     almost certainly created on a 16-bit machine, and contain headers	made  up
     of  five  fields.	 The fields are the object name (8 characters), the file
     last modification time (type long), the user id (type char), the file  mode
     (type char) and the file size (type unsigned int).  Files were padded to an
     even number of bytes.

     The  second  was denoted by the leading ``magic'' number 0177545 (stored as
     type int).  These archives may have been created on either 16 or 32-bit ma-
     chines, and contain headers made up of six fields.  The fields are the  ob-
     ject name (14 characters), the file last modification time (type long), the
     user and group id's (each type char), the file mode (type int) and the file
     size  (type long).  Files were padded to an even number of bytes.	For more
     information on converting from this format see arcv(8).

     The current archive format (without support for long  character  names  and
     names with embedded spaces) was introduced in 4.0BSD.  The headers were the
     same  as  the  current format, with the exception that names longer than 16
     characters were truncated, and names with embedded spaces (and often trail-
     ing spaces) were not supported.  It has been extended for these reasons, as
     described above.  This format is currently under development.

COMPATIBILITY
     No archive format is currently specified by any standard.	 AT&T  System  V
     UNIX  has	historically distributed archives in a different format from all
     of the above.

net2				  May 10, 1991				   AR(5)
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