2.11BSD#431 - /usr/man/cat5/ar.0

AR(5)               UNIX Programmer's 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 charac-
     ters), 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
     following the archive header.

     Any unused characters in any of these fields are written as
     space characters.  If any fields are their particular max-
     imum 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)


Printed 11/24/99       September 24, 1993                       1


AR(5)               UNIX Programmer's Manual                AR(5)


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 con-
     verting from this format see arcv(8).

     The current archive format (without support for long charac-
     ter 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 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.


Printed 11/24/99       September 24, 1993                       2