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.\" $FreeBSD$

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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.