The archive command ar combines several files into one. Archives are used mainly as libraries to be searched by the link-editor ld.
A file produced by ar has a magic string 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:
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The name is a blank-padded string. The ar_fmag field contains ARFMAG to help verify the presence of a header. The other fields are left-adjusted, blank-padded numbers. They are decimal except for ar_mode, which is octal. The date is the modification date of the file at the time of its insertion into the archive.
Each file begins on a even (0 mod 2) boundary; a new-line is inserted between files if necessary. Nevertheless the size given reflects the actual size of the file exclusive of padding.
There is no provision for empty areas in an archive file.
The encoding of the header is portable across machines. If an archive contains printable files, the archive itself is printable.