AR(6) AR(6)
NAME
ar - archive (library) file format
SYNOPSIS
#include <ar.h>
DESCRIPTION
The archive command ar(1) is used to combine several files
into one. Archives are used mainly as libraries to be
searched by the loaders 2l(1) et al.
A file produced by ar has a magic string at the start, fol-
lowed by the constituent files, each preceded by a file
header. The magic number and header layout as described in
the include file are:
#define ARMAG "!<arch>\n"
#define SARMAG 8
#define ARFMAG "`\n"
struct ar_hdr {
char name[16];
char date[12];
char uid[6];
char gid[6];
char mode[8];
char size[10];
char fmag[2];
};
#define SAR_HDR 60
The name is a blank-padded string. The `fmag' field con-
tains `ARFMAG' to help verify the presence of a header. The
other fields are left-adjusted, blank-padded numbers. They
are decimal except for `mode', which is octal. The date is
the modification date of the file (see stat(2)) at the time
of its insertion into the archive. The mode is the low 9
bits of the file permission mode. The length of the header
is `SAR_HDR'. Because the `ar_hdr' structure is padded in
an architecture-dependent manner, the structure should never
be read or written as a unit; instead, each field should be
read or written independently.
Each file begins on an even (0 mod 2) boundary; a newline is
inserted between files if necessary. Nevertheless size
reflects the actual size of the file exclusive of padding.
When all members of an archive are object files of the same
architecture, ar automatically adds an extra file, named
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AR(6) AR(6)
__.SYMDEF, as the first member of the archive. This file
contains an index used by the loaders to locate all exter-
nally defined text and data symbols in the archive.
There is no provision for empty areas in an archive file.
SEE ALSO
ar(1), 2l(1), nm(1), stat(2)
BUGS
The uid and gid fields are unused in Plan 9. They provide
compatibility with Unix ar format.
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