LIBARCHIVE(3) LIBARCHIVE(3)
March 18, 2012
NAME
libarchive - functions for reading and writing streaming archives
OVERVIEW
The libarchive library provides a flexible interface for reading and
writing archives in various formats such as tar and cpio. libarchive
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 ``ustar'' format,
+ the POSIX ``pax interchange'' format,
+ GNU-format tar archives,
+ most common cpio archive formats,
+ ISO9660 CD images (including RockRidge and Joliet
extensions),
+ Zip archives,
+ ar archives (including GNU/SysV and BSD extensions),
+ Microsoft CAB archives,
+ LHA archives,
+ mtree file tree descriptions,
+ RAR archives,
+ XAR archives.
The library automatically detects archives compressed with gzip(1),
bzip2(1), xz(1), lzip(1), or compress(1) and decompresses them
transparently. It can similarly detect and decode archives processed
with uuencode(1) or which have an rpm(1) header.
When writing an archive, you can specify the compression to be used
and the format to use. The library can write
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+ POSIX-standard ``ustar'' archives,
+ POSIX ``pax interchange format'' archives,
+ POSIX octet-oriented cpio archives,
+ Zip archive,
+ two different variants of shar archives,
+ ISO9660 CD images,
+ 7-Zip archives,
+ ar archives,
+ mtree file tree descriptions,
+ XAR archives.
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 by POSIX-compliant pax(1)
implementations on many systems as well as several newer
implementations of tar(1). 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 archive_read_XXX()
functions and the archive_write_XXX() functions, respectively, and
either can be used independently of the other.
The rest of this manual page provides an overview of the library
operation. More detailed information can be found in the individual
manual pages for each API or utility function.
READING AN ARCHIVE
See archive_read(3).
WRITING AN ARCHIVE
See archive_write(3).
WRITING ENTRIES TO DISK
The archive_write_disk(3) API allows you to write archive_entry(3)
objects to disk using the same API used by archive_write(3). The
archive_write_disk(3) API is used internally by
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 operations.
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READING ENTRIES FROM DISK
The archive_read_disk(3) supports for populating archive_entry(3)
objects from information in the filesystem. This includes the
information accessible from the stat(2) system call as well as ACLs,
extended attributes, and other metadata. The archive_read_disk(3) API
also supports iterating over directory trees, which allows directories
of files to be read using an API compatible with the archive_read(3)
API.
DESCRIPTION
Detailed descriptions of each function are provided by the
corresponding manual pages.
All of the functions utilize an opaque Tn struct archive datatype that
provides access to the archive contents.
The Tn struct archive_entry structure contains a complete description
of a single archive entry. It uses an opaque interface that is fully
documented in archive_entry(3).
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 PATH_MAX.
RETURN VALUES
Most functions return ARCHIVE_OK (zero) on success, non-zero on error.
The return value indicates the general severity of the error, ranging
from ARCHIVE_WARN, which indicates a minor problem that should
probably be reported to the user, to ARCHIVE_FATAL, which indicates a
serious problem that will prevent any further operations on this
archive. On error, the archive_errno() function can be used to
retrieve a numeric error code (see errno(2)). The
archive_error_string() returns a textual error message suitable for
display.
archive_read_new() and archive_write_new() return pointers to an
allocated and initialized Tn struct archive object.
archive_read_data() and archive_write_data() 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 archive_errno() and archive_error_string()
functions can be used to obtain more information.
ENVIRONMENT
There are character set conversions within the archive_entry(3)
functions that are impacted by the currently-selected locale.
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SEE ALSO
tar(1), archive_entry(3), archive_read(3), archive_util(3),
archive_write(3), tar(5)
HISTORY
The libarchive library first appeared in FreeBSD 5.3.
AUTHORS
-nosplit The libarchive library was originally written by Tim Kientzle
<kientzle@acm.org.>
BUGS
Some archive formats support information that is not supported by Tn
struct archive_entry. 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 Tn struct archive_entry 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.
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