V4/man/man5/ar.5

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.th ARCHIVE V 9/10/73
.sh NAME
ar \*- archive (library) file format
.sh DESCRIPTION
The archive command
.it ar
is used to combine several files into
one.
Archives are used mainly as libraries to be searched
by the link-editor
.it ld.
.s3
A file produced by
.it ar
has a magic number at the start,
followed by the constituent files, each preceded by a file header.
The magic number is
177555(8)
(it was chosen to be unlikely to occur anywhere else).
The header of each file is 16 bytes long:
.s3
.lp +13 8
0-7	file
name, null padded on the right
.lp +13 8
8-11	modification
time of the file
.lp +13 8
12	user ID of file owner
.lp +13 8
13	file mode
.lp +13 8
14-15	file size
.s3
.i0
If the file is an odd number of bytes long, it is padded
with a null byte, but the size in the header is correct.
.s3
Notice there is no provision for empty areas in an archive
file.
.sh "SEE ALSO"
ar (I), ld (I)
.sh BUGS
Names are only 8 characters, not 14.
More important, there isn't enough room to
store the proper mode,
so
.it ar
always extracts in mode 666.