The original files' contents, mode (permissions), timestamp, owner, and group are preserved in the archive, and can be restored on extraction.
GNU 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.
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 ar called ranlib can be used to add just the table.
GNU 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. For security reasons absolute paths and paths with a "/../" component are not allowed.
GNU 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.
If you wish, you may begin the first command-line argument with a dash.
The p keyletter specifies what operation to execute; it may be any of the following, but you must specify only one of them:
If you specify the v modifier, ar lists each module as it is deleted.
The ordering of members in an archive can make a difference in how programs are linked using the library, if a symbol is defined in more than one member.
If no modifiers are used with "m", any members you name in the member arguments are moved to the end of the archive; you can use the a, b, or i modifiers to move them to a specified place instead.
If you specify no member arguments, all the files in the archive are printed.
The modifiers a, b, and i do not affect this operation; new members are always placed at the end of the archive.
The modifier v makes ar list each file as it is appended.
Since the point of this operation is speed, implementations of ar have the option of not updating the archive's symbol table if one exists. Too many different systems however assume that symbol tables are always up-to-date, so GNU ar will rebuild the table even with a quick append.
Note - GNU ar treats the command qs as a synonym for r - replacing already existing files in the archive and appending new ones at the end.
If one of the files named in member... does not exist, ar displays an error message, and leaves undisturbed any existing members of the archive matching that name.
By default, new members are added at the end of the file; but you may use one of the modifiers a, b, or i to request placement relative to some existing member.
The modifier v used with this operation elicits a line of output for each file inserted, along with one of the letters a or r to indicate whether the file was appended (no old member deleted) or replaced.
If you do not specify a member, all files in the archive are listed.
If there is more than one file with the same name (say, fie) in an archive (say b.a), ar t b.a fie lists only the first instance; to see them all, you must ask for a complete listing---in our example, ar t b.a.
If you do not specify a member, all files in the archive are extracted.
Files cannot be extracted from a thin archive.
A number of modifiers (mod) may immediately follow the p keyletter, to specify variations on an operation's behavior:
If binutils was configured with --enable-deterministic-archives, then this mode is on by default. It can be disabled with the U modifier, below.
This is the default unless binutils was configured with --enable-deterministic-archives.
ar ignores an initial option spelt -X32_64, for compatibility with AIX. The behaviour produced by this option is the default for GNU ar. ar does not support any of the other -X options; in particular, it does not support -X32 which is the default for AIX ar.
The optional command line switch --plugin name causes ar to load the plugin called name which adds support for more file formats. This option is only available if the toolchain has been built with plugin support enabled.
The optional command line switch --target bfdname specifies that the archive members are in an object code format different from your system's default format. See
Options in file are separated by whitespace. A whitespace character may be included in an option by surrounding the entire option in either single or double quotes. Any character (including a backslash) may be included by prefixing the character to be included with a backslash. The file may itself contain additional @file options; any such options will be processed recursively.
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