libarchive/libarchive.3

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.Dd March 18, 2012
.Dt LIBARCHIVE 3
.Os
.Sh NAME
.Nm libarchive
.Nd functions for reading and writing streaming archives
.Sh OVERVIEW
The
.Nm
library provides a flexible interface for reading and writing
archives in various formats such as tar and cpio.
.Nm
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.
.Pp
When reading an archive, the library automatically detects the
format and the compression.
The library currently has read support for:
.Bl -bullet -compact
.It
old-style tar archives,
.It
most variants of the POSIX
.Dq ustar
format,
.It
the POSIX
.Dq pax interchange
format,
.It
GNU-format tar archives,
.It
most common cpio archive formats,
.It
ISO9660 CD images (including RockRidge and Joliet extensions),
.It
Zip archives,
.It
ar archives (including GNU/SysV and BSD extensions),
.It
Microsoft CAB archives,
.It
LHA archives,
.It
mtree file tree descriptions,
.It
RAR archives,
.It
XAR archives.
.El
The library automatically detects archives compressed with
.Xr gzip 1 ,
.Xr bzip2 1 ,
.Xr xz 1 ,
.Xr lzip 1 ,
or
.Xr compress 1
and decompresses them transparently.
It can similarly detect and decode archives processed with
.Xr uuencode 1
or which have an
.Xr rpm 1
header.
.Pp
When writing an archive, you can specify the compression
to be used and the format to use.
The library can write
.Bl -bullet -compact
.It
POSIX-standard
.Dq ustar
archives,
.It
POSIX
.Dq pax interchange format
archives,
.It
POSIX octet-oriented cpio archives,
.It
Zip archive,
.It
two different variants of shar archives,
.It
ISO9660 CD images,
.It
7-Zip archives,
.It
ar archives,
.It
mtree file tree descriptions,
.It
XAR archives.
.El
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
.Xr pax 1
implementations on many systems as well as several newer implementations of
.Xr 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.
.Pp
The read and write APIs are accessed through the
.Fn archive_read_XXX
functions and the
.Fn archive_write_XXX
functions, respectively, and either can be used independently
of the other.
.Pp
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.
.\"
.Sh READING AN ARCHIVE
See
.Xr archive_read 3 .
.\"
.Sh WRITING AN ARCHIVE
See
.Xr archive_write 3 .
.\"
.Sh WRITING ENTRIES TO DISK
The
.Xr archive_write_disk 3
API allows you to write
.Xr archive_entry 3
objects to disk using the same API used by
.Xr archive_write 3 .
The
.Xr archive_write_disk 3
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
operations.
.Sh READING ENTRIES FROM DISK
The
.Xr archive_read_disk 3
supports for populating
.Xr archive_entry 3
objects from information in the filesystem.
This includes the information accessible from the
.Xr stat 2
system call as well as ACLs, extended attributes,
and other metadata.
The
.Xr 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
.Xr archive_read 3
API.
.Sh DESCRIPTION
Detailed descriptions of each function are provided by the
corresponding manual pages.
.Pp
All of the functions utilize an opaque
.Tn struct archive
datatype that provides access to the archive contents.
.Pp
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
.Xr archive_entry 3 .
.Pp
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
.Va PATH_MAX .
.Sh RETURN VALUES
Most functions return
.Cm ARCHIVE_OK
(zero) on success, non-zero on error.
The return value indicates the general severity of the error, ranging
from
.Cm ARCHIVE_WARN ,
which indicates a minor problem that should probably be reported
to the user, to
.Cm ARCHIVE_FATAL ,
which indicates a serious problem that will prevent any further
operations on this archive.
On error, the
.Fn archive_errno
function can be used to retrieve a numeric error code (see
.Xr errno 2 ) .
The
.Fn archive_error_string
returns a textual error message suitable for display.
.Pp
.Fn archive_read_new
and
.Fn archive_write_new
return pointers to an allocated and initialized
.Tn struct archive
object.
.Pp
.Fn archive_read_data
and
.Fn 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
.Fn archive_errno
and
.Fn archive_error_string
functions can be used to obtain more information.
.Sh ENVIRONMENT
There are character set conversions within the
.Xr archive_entry 3
functions that are impacted by the currently-selected locale.
.Sh SEE ALSO
.Xr tar 1 ,
.Xr archive_entry 3 ,
.Xr archive_read 3 ,
.Xr archive_util 3 ,
.Xr archive_write 3 ,
.Xr tar 5
.Sh HISTORY
The
.Nm libarchive
library first appeared in
.Fx 5.3 .
.Sh AUTHORS
.An -nosplit
The
.Nm libarchive
library was originally written by
.An Tim Kientzle Aq kientzle@acm.org .
.Sh 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.
.Pp
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.
.Pp
The ISO9660 reader cannot yet read all ISO9660 images;
it should learn how to seek.
.Pp
The AR writer requires the client program to use
two passes, unlike all other libarchive writers.