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AR(5)			  FreeBSD 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	con-
     tents 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
     characters).  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 follow-
     ing 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'')
     character,	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
     machines, and contain headers made	up of six fields.  The fields are the
     object 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
     trailing spaces) were not supported.  It has been extended	for these rea-
     sons, 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.

FreeBSD	11.0			 May 10, 1991			  FreeBSD 11.0

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | COMPATIBILITY

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