ar [-]p[mod] [--plugin name] [--target bfdname] [--output dirname] [--record-libdeps libdeps] [relpos] [count] archive [member] ar -M [ <mri-script ]
ar program creates, modifies, and extracts from archives. An archive is a single file holding a collection of other files in a structure that makes it possible to retrieve the original individual files (called members of the archive).
The original files contents, mode (permissions), timestamp, owner, and group are preserved in the archive, and can be restored on extraction.
ar can maintain archives whose members have names of any length; however, depending on how
ar is configured on your system, a limit on member-name length may be imposed for compatibility with archive formats maintained with other tools. If it exists, the limit is often 15 characters (typical of formats related to a.out) or 16 characters (typical of formats related to coff).
ar is considered a binary utility because archives of this sort are most often used as libraries holding commonly needed subroutines. Since libraries often will depend on other libraries,
ar can also record the dependencies of a library when the --record-libdeps option is specified.
ar creates an index to the symbols defined in relocatable object modules in the archive when you specify the modifier s. Once created, this index is updated in the archive whenever
ar makes a change to its contents (save for the q update operation). An archive with such an index speeds up linking to the library, and allows routines in the library to call each other without regard to their placement in the archive.
You may use nm -s or nm --print-armap to list this index table. If an archive lacks the table, another form of
ranlib can be used to add just the table.
ar can optionally create a thin archive, which contains a symbol index and references to the original copies of the member files of the archive. This is useful for building libraries for use within a local build tree, where the relocatable objects are expected to remain available, and copying the contents of each object would only waste time and space.
An archive can either be thin or it can be normal. It cannot be both at the same time. Once an archive is created its format cannot be changed without first deleting it and then creating a new archive in its place.
Thin archives are also flattened, so that adding one thin archive to another thin archive does not nest it, as would happen with a normal archive. Instead the elements of the first archive are added individually to the second archive.
The paths to the elements of the archive are stored relative to the archive itself.
ar is designed to be compatible with two different facilities. You can control its activity using command-line options, like the different varieties of
ar on Unix systems; or, if you specify the single command-line option -M, you can control it with a script supplied via standard input, like the MRI librarian program.