AR(5) File Formats Manual AR(5)
ar - archive (library) file format
The archive command ar is used to combine several files into one. Ar-
chives are used mainly as libraries to be searched by the link-editor
A file produced by ar has a magic number at the start, followed by the
constituent files, each preceded by a file header. The magic number
and header layout as described in the include file are:
/* Header describing `ar' archive file format.
Copyright (C) 1996-2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
#define _AR_H 1
/* Archive files start with the ARMAG identifying string. Then follows a
`struct ar_hdr', and as many bytes of member file data as its `ar_size'
member indicates, for each member file. */
#define ARMAG "!<arch>0/* String that begins an archive file. */
#define SARMAG8/* Size of that string. */
#define ARFMAG"`0/* String in ar_fmag at end of each header. */
char ar_name;/* Member file name, sometimes / terminated. */
char ar_date;/* File date, decimal seconds since Epoch. */
char ar_uid, ar_gid;/* User and group IDs, in ASCII decimal. */
char ar_mode;/* File mode, in ASCII octal. */
char ar_size;/* File size, in ASCII decimal. */
char ar_fmag;/* Always contains ARFMAG. */
#endif /* ar.h */
The name is a null-terminated string; the date is in the form of
time(2); the user ID and group ID are numbers; the mode is a bit pat-
tern per chmod(2); the size is counted in bytes.
Each file begins on a word boundary; a null byte is inserted between
files if necessary. Nevertheless the size given reflects the actual
size of the file exclusive of padding.
Notice there is no provision for empty areas in an archive file.
ar(1), ld(1), nm(1)
Coding user and group IDs as characters is a botch.