Section: C Library Functions (3)
- functions for reading and writing streaming archives
library provides a flexible interface for reading and writing
archives in various formats such as tar and cpio.
also supports reading and writing archives compressed using
various compression filters such as gzip and bzip2.
The library is inherently stream-oriented; readers serially iterate through
the archive, writers serially add things to the archive.
In particular, note that there is currently no built-in support for
random access nor for in-place modification.
When reading an archive, the library automatically detects the
format and the compression.
The library currently has read support for:
old-style tar archives,
most variants of the POSIX
GNU-format tar archives,
most common cpio archive formats,
ISO9660 CD images (including RockRidge and Joliet extensions),
ar archives (including GNU/SysV and BSD extensions),
Microsoft CAB archives,
mtree file tree descriptions,
The library automatically detects archives compressed with
and decompresses them transparently.
It can similarly detect and decode archives processed with
or which have an
When writing an archive, you can specify the compression
to be used and the format to use.
The library can write
``pax interchange format''
POSIX octet-oriented cpio archives,
two different variants of shar archives,
ISO9660 CD images,
mtree file tree descriptions,
Pax interchange format is an extension of the tar archive format that
eliminates essentially all of the limitations of historic tar formats
in a standard fashion that is supported
implementations on many systems as well as several newer implementations of
Note that the default write format will suppress the pax extended
attributes for most entries; explicitly requesting pax format will
enable those attributes for all entries.
The read and write APIs are accessed through the
functions and the
functions, respectively, and either can be used independently
of the other.
The rest of this manual page provides an overview of the library
More detailed information can be found in the individual manual
pages for each API or utility function.
READING AN ARCHIVE
WRITING AN ARCHIVE
WRITING ENTRIES TO DISK
API allows you to write
objects to disk using the same API used by
API is used internally by
Fn archive_read_extract ;
using it directly can provide greater control over how entries
get written to disk.
This API also makes it possible to share code between
archive-to-archive copy and archive-to-disk extraction
READING ENTRIES FROM DISK
supports for populating
objects from information in the filesystem.
This includes the information accessible from the
system call as well as ACLs, extended attributes,
and other metadata.
API also supports iterating over directory trees,
which allows directories of files to be read using
an API compatible with
Detailed descriptions of each function are provided by the
corresponding manual pages.
All of the functions utilize an opaque
datatype that provides access to the archive contents.
structure contains a complete description of a single archive
It uses an opaque interface that is fully documented in
Users familiar with historic formats should be aware that the newer
variants have eliminated most restrictions on the length of textual fields.
Clients should not assume that filenames, link names, user names, or
group names are limited in length.
In particular, pax interchange format can easily accommodate pathnames
in arbitrary character sets that exceed
Most functions return
(zero) on success, non-zero on error.
The return value indicates the general severity of the error, ranging
which indicates a minor problem that should probably be reported
to the user, to
which indicates a serious problem that will prevent any further
operations on this archive.
On error, the
function can be used to retrieve a numeric error code (see
returns a textual error message suitable for display.
return pointers to an allocated and initialized
return a count of the number of bytes actually read or written.
A value of zero indicates the end of the data for this entry.
A negative value indicates an error, in which case the
functions can be used to obtain more information.
There are character set conversions within the
functions that are impacted by the currently-selected locale.
library first appeared in
Fx 5.3 .
library was originally written by
An Tim Kientzle Aq email@example.com
Some archive formats support information that is not supported by
Such information cannot be fully archived or restored using this library.
This includes, for example, comments, character sets,
or the arbitrary key/value pairs that can appear in
pax interchange format archives.
Conversely, of course, not all of the information that can be
stored in an
is supported by all formats.
For example, cpio formats do not support nanosecond timestamps;
old tar formats do not support large device numbers.
The ISO9660 reader cannot yet read all ISO9660 images;
it should learn how to seek.
The AR writer requires the client program to use
two passes, unlike all other libarchive writers.