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

     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.