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25.\" $FreeBSD$
26.\"
27.Dd March 18, 2012
28.Dt LIBARCHIVE 3
29.Os
30.Sh NAME
31.Nm libarchive
32.Nd functions for reading and writing streaming archives
33.Sh OVERVIEW
34The
35.Nm
36library provides a flexible interface for reading and writing
37archives in various formats such as tar and cpio.
38.Nm
39also supports reading and writing archives compressed using
40various compression filters such as gzip and bzip2.
41The library is inherently stream-oriented; readers serially iterate through
42the archive, writers serially add things to the archive.
43In particular, note that there is currently no built-in support for
44random access nor for in-place modification.
45.Pp
46When reading an archive, the library automatically detects the
47format and the compression.
48The library currently has read support for:
49.Bl -bullet -compact
50.It
51old-style tar archives,
52.It
53most variants of the POSIX
54.Dq ustar
55format,
56.It
57the POSIX
58.Dq pax interchange
59format,
60.It
61GNU-format tar archives,
62.It
63most common cpio archive formats,
64.It
657-Zip archives,
66.It
67ar archives (including GNU/SysV and BSD extensions),
68.It
69Microsoft CAB archives,
70.It
71ISO9660 CD images (including RockRidge and Joliet extensions),
72.It
73LHA archives,
74.It
75mtree file tree descriptions,
76.It
77RAR and most RAR5 archives,
78.It
79WARC archives,
80.It
81XAR archives,
82.It
83Zip archives.
84.El
85The library automatically detects archives compressed with
86.Xr compress 1 ,
87.Xr bzip2 1 ,
88.Xr grzip 1 ,
89.Xr gzip 1 ,
90.Xr lrzip 1 ,
91.Xr lz4 1 ,
92.Xr lzip 1 ,
93.Xr lzop 1 ,
94.Xr xz 1 ,
95or
96.Xr zstd 1
97and decompresses them transparently. Decompression of some formats
98requires external decompressor utilities.
99It can similarly detect and decode archives processed with
100.Xr uuencode 1
101or which have an
102.Xr rpm 1
103header.
104.Pp
105When writing an archive, you can specify the compression
106to be used and the format to use.
107The library can write
108.Bl -bullet -compact
109.It
110POSIX-standard
111.Dq ustar
112archives,
113.It
114POSIX
115.Dq pax interchange format
116archives,
117.It
118cpio archives,
119.It
1207-Zip archives,
121.It
122ar archives,
123.It
124two different variants of shar archives,
125.It
126ISO9660 CD images,
127.It
128mtree file tree descriptions,
129.It
130XAR archives,
131.It
132Zip archive.
133.El
134Pax interchange format is an extension of the tar archive format that
135eliminates essentially all of the limitations of historic tar formats
136in a standard fashion that is supported
137by POSIX-compliant
138.Xr pax 1
139implementations on many systems as well as several newer implementations of
140.Xr tar 1 .
141Note that the default write format will suppress the pax extended
142attributes for most entries; explicitly requesting pax format will
143enable those attributes for all entries.
144.Pp
145The read and write APIs are accessed through the
146.Fn archive_read_XXX
147functions and the
148.Fn archive_write_XXX
149functions, respectively, and either can be used independently
150of the other.
151.Pp
152The rest of this manual page provides an overview of the library
153operation.
154More detailed information can be found in the individual manual
155pages for each API or utility function.
156.\"
157.Sh READING AN ARCHIVE
158See
159.Xr archive_read 3 .
160.\"
161.Sh WRITING AN ARCHIVE
162See
163.Xr archive_write 3 .
164.\"
165.Sh WRITING ENTRIES TO DISK
166The
167.Xr archive_write_disk 3
168API allows you to write
169.Xr archive_entry 3
170objects to disk using the same API used by
171.Xr archive_write 3 .
172The
173.Xr archive_write_disk 3
174API is used internally by
175.Fn archive_read_extract ;
176using it directly can provide greater control over how entries
177get written to disk.
178This API also makes it possible to share code between
179archive-to-archive copy and archive-to-disk extraction
180operations.
181.Sh READING ENTRIES FROM DISK
182The
183.Xr archive_read_disk 3
184supports for populating
185.Xr archive_entry 3
186objects from information in the filesystem.
187This includes the information accessible from the
188.Xr stat 2
189system call as well as ACLs, extended attributes,
190and other metadata.
191The
192.Xr archive_read_disk 3
193API also supports iterating over directory trees,
194which allows directories of files to be read using
195an API compatible with
196the
197.Xr archive_read 3
198API.
199.Sh DESCRIPTION
200Detailed descriptions of each function are provided by the
201corresponding manual pages.
202.Pp
203All of the functions utilize an opaque
204.Tn struct archive
205datatype that provides access to the archive contents.
206.Pp
207The
208.Tn struct archive_entry
209structure contains a complete description of a single archive
210entry.
211It uses an opaque interface that is fully documented in
212.Xr archive_entry 3 .
213.Pp
214Users familiar with historic formats should be aware that the newer
215variants have eliminated most restrictions on the length of textual fields.
216Clients should not assume that filenames, link names, user names, or
217group names are limited in length.
218In particular, pax interchange format can easily accommodate pathnames
219in arbitrary character sets that exceed
220.Va PATH_MAX .
221.Sh RETURN VALUES
222Most functions return
223.Cm ARCHIVE_OK
224(zero) on success, non-zero on error.
225The return value indicates the general severity of the error, ranging
226from
227.Cm ARCHIVE_WARN ,
228which indicates a minor problem that should probably be reported
229to the user, to
230.Cm ARCHIVE_FATAL ,
231which indicates a serious problem that will prevent any further
232operations on this archive.
233On error, the
234.Fn archive_errno
235function can be used to retrieve a numeric error code (see
236.Xr errno 2 ) .
237The
238.Fn archive_error_string
239returns a textual error message suitable for display.
240.Pp
241.Fn archive_read_new
242and
243.Fn archive_write_new
244return pointers to an allocated and initialized
245.Tn struct archive
246object.
247.Pp
248.Fn archive_read_data
249and
250.Fn archive_write_data
251return a count of the number of bytes actually read or written.
252A value of zero indicates the end of the data for this entry.
253A negative value indicates an error, in which case the
254.Fn archive_errno
255and
256.Fn archive_error_string
257functions can be used to obtain more information.
258.Sh ENVIRONMENT
259There are character set conversions within the
260.Xr archive_entry 3
261functions that are impacted by the currently-selected locale.
262.Sh SEE ALSO
263.Xr tar 1 ,
264.Xr archive_entry 3 ,
265.Xr archive_read 3 ,
266.Xr archive_util 3 ,
267.Xr archive_write 3 ,
268.Xr tar 5
269.Sh HISTORY
270The
271.Nm libarchive
272library first appeared in
273.Fx 5.3 .
274.Sh AUTHORS
275.An -nosplit
276The
277.Nm libarchive
278library was originally written by
279.An Tim Kientzle Aq kientzle@acm.org .
280.Sh BUGS
281Some archive formats support information that is not supported by
282.Tn struct archive_entry .
283Such information cannot be fully archived or restored using this library.
284This includes, for example, comments, character sets,
285or the arbitrary key/value pairs that can appear in
286pax interchange format archives.
287.Pp
288Conversely, of course, not all of the information that can be
289stored in an
290.Tn struct archive_entry
291is supported by all formats.
292For example, cpio formats do not support nanosecond timestamps;
293old tar formats do not support large device numbers.
294.Pp
295The ISO9660 reader cannot yet read all ISO9660 images;
296it should learn how to seek.
297.Pp
298The AR writer requires the client program to use
299two passes, unlike all other libarchive writers.
300