#summary LIBARCHIVE 3 manual page
== NAME ==
*libarchive*
- functions for reading and writing streaming archives
== LIBRARY ==
Lb libarchive
== 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:
<ul>
<li>
old-style tar archives,
</li><li>
most variants of the POSIX
"ustar"
format,
</li><li>
the POSIX
"pax interchange"
format,
</li><li>
GNU-format tar archives,
</li><li>
most common cpio archive formats,
</li><li>
ISO9660 CD images (including RockRidge and Joliet extensions),
</li><li>
Zip archives.
</li></ul>
The library automatically detects archives compressed with
*gzip*(1),
*bzip2*(1),
*xz*(1),
or
*compress*(1)
and decompresses them transparently.

When writing an archive, you can specify the compression
to be used and the format to use.
The library can write
<ul>
<li>
POSIX-standard
"ustar"
archives,
</li><li>
POSIX
"pax interchange format"
archives,
</li><li>
POSIX octet-oriented cpio archives,
</li><li>
Zip archive,
</li><li>
two different variants of shar archives.
</li></ul>
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
*libarchive_read*(3).
== WRITING AN ARCHIVE ==
See
*libarchive_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.
== READING ENTRIES FROM DISK ==
The
*archive_read_disk*(3)
provides some support for populating
*archive_entry*(3)
objects from information in the filesystem.
== DESCRIPTION ==
Detailed descriptions of each function are provided by the
corresponding manual pages.

All of the functions utilize an opaque
*struct archive*
datatype that provides access to the archive contents.

The
*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
*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.
== 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 ==
The
*libarchive*
library was written by
Tim Kientzle  <kientzle@acm.org.>
== BUGS ==
Some archive formats support information that is not supported by
*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
*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
*archive_read_disk*(3)
API should support iterating over filesystems;
that would make it possible to share code among
disk-to-archive, archive-to-archive, archive-to-disk,
and disk-to-disk operations.
Currently, it only supports reading the
information for a single file.
(Which is still quite useful, as it hides a lot
of system-specific details.)
