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257 lines
7.6 KiB
Text
257 lines
7.6 KiB
Text
LIBARCHIVE(3) manual page
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== NAME ==
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'''libarchive'''
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- functions for reading and writing streaming archives
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== OVERVIEW ==
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The
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'''libarchive'''
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library provides a flexible interface for reading and writing
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archives in various formats such as tar and cpio.
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'''libarchive'''
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also supports reading and writing archives compressed using
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various compression filters such as gzip and bzip2.
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The library is inherently stream-oriented; readers serially iterate through
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the archive, writers serially add things to the archive.
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In particular, note that there is currently no built-in support for
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random access nor for in-place modification.
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When reading an archive, the library automatically detects the
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format and the compression.
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The library currently has read support for:
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<ul>
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<li>
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old-style tar archives,
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</li><li>
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most variants of the POSIX
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"ustar"
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format,
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</li><li>
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the POSIX
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"pax interchange"
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format,
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</li><li>
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GNU-format tar archives,
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</li><li>
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most common cpio archive formats,
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</li><li>
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ISO9660 CD images (including RockRidge and Joliet extensions),
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</li><li>
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Zip archives,
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</li><li>
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ar archives (including GNU/SysV and BSD extensions),
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</li><li>
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Microsoft CAB archives,
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</li><li>
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LHA archives,
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</li><li>
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mtree file tree descriptions,
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</li><li>
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RAR archives,
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</li><li>
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XAR archives.
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</li></ul>
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The library automatically detects archives compressed with
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[[gzip(1)|http://www.freebsd.org/cgi/man.cgi?query=gzip&sektion=1]],
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[[bzip2(1)|http://www.freebsd.org/cgi/man.cgi?query=bzip2&sektion=1]],
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[[xz(1)|http://www.freebsd.org/cgi/man.cgi?query=xz&sektion=1]],
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[[lzip(1)|http://www.freebsd.org/cgi/man.cgi?query=lzip&sektion=1]],
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or
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[[compress(1)|http://www.freebsd.org/cgi/man.cgi?query=compress&sektion=1]]
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and decompresses them transparently.
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It can similarly detect and decode archives processed with
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[[uuencode(1)|http://www.freebsd.org/cgi/man.cgi?query=uuencode&sektion=1]]
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or which have an
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[[rpm(1)|http://www.freebsd.org/cgi/man.cgi?query=rpm&sektion=1]]
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header.
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When writing an archive, you can specify the compression
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to be used and the format to use.
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The library can write
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<ul>
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<li>
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POSIX-standard
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"ustar"
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archives,
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</li><li>
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POSIX
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"pax interchange format"
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archives,
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</li><li>
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POSIX octet-oriented cpio archives,
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</li><li>
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Zip archive,
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</li><li>
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two different variants of shar archives,
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</li><li>
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ISO9660 CD images,
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</li><li>
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7-Zip archives,
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</li><li>
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ar archives,
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</li><li>
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mtree file tree descriptions,
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</li><li>
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XAR archives.
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</li></ul>
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Pax interchange format is an extension of the tar archive format that
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eliminates essentially all of the limitations of historic tar formats
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in a standard fashion that is supported
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by POSIX-compliant
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[[pax(1)|http://www.freebsd.org/cgi/man.cgi?query=pax&sektion=1]]
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implementations on many systems as well as several newer implementations of
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[[ManPageBsdtar1]].
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Note that the default write format will suppress the pax extended
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attributes for most entries; explicitly requesting pax format will
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enable those attributes for all entries.
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The read and write APIs are accessed through the
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'''archive_read_XXX'''()
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functions and the
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'''archive_write_XXX'''()
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functions, respectively, and either can be used independently
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of the other.
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The rest of this manual page provides an overview of the library
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operation.
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More detailed information can be found in the individual manual
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pages for each API or utility function.
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== READING AN ARCHIVE ==
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See
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[[ManPagerchiveead3]].
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== WRITING AN ARCHIVE ==
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See
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[[ManPagerchiverite3]].
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== WRITING ENTRIES TO DISK ==
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The
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[[ManPagerchiveriteisk3]]
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API allows you to write
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[[ManPagerchiventry3]]
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objects to disk using the same API used by
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[[ManPagerchiverite3]].
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The
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[[ManPagerchiveriteisk3]]
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API is used internally by
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'''archive_read_extract'''('';'')
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using it directly can provide greater control over how entries
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get written to disk.
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This API also makes it possible to share code between
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archive-to-archive copy and archive-to-disk extraction
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operations.
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== READING ENTRIES FROM DISK ==
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The
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[[ManPagerchiveeadisk3]]
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supports for populating
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[[ManPagerchiventry3]]
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objects from information in the filesystem.
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This includes the information accessible from the
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[[stat(2)|http://www.freebsd.org/cgi/man.cgi?query=stat&sektion=2]]
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system call as well as ACLs, extended attributes,
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and other metadata.
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The
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[[ManPagerchiveeadisk3]]
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API also supports iterating over directory trees,
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which allows directories of files to be read using
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an API compatible with
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the
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[[ManPagerchiveead3]]
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API.
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== DESCRIPTION ==
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Detailed descriptions of each function are provided by the
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corresponding manual pages.
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All of the functions utilize an opaque
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'''struct archive'''
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datatype that provides access to the archive contents.
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The
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'''struct archive_entry'''
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structure contains a complete description of a single archive
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entry.
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It uses an opaque interface that is fully documented in
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[[ManPagerchiventry3]].
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Users familiar with historic formats should be aware that the newer
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variants have eliminated most restrictions on the length of textual fields.
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Clients should not assume that filenames, link names, user names, or
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group names are limited in length.
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In particular, pax interchange format can easily accommodate pathnames
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in arbitrary character sets that exceed
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''PATH_MAX''.
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== RETURN VALUES ==
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Most functions return
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'''ARCHIVE_OK'''
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(zero) on success, non-zero on error.
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The return value indicates the general severity of the error, ranging
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from
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'''ARCHIVE_WARN''',
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which indicates a minor problem that should probably be reported
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to the user, to
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'''ARCHIVE_FATAL''',
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which indicates a serious problem that will prevent any further
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operations on this archive.
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On error, the
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'''archive_errno'''()
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function can be used to retrieve a numeric error code (see
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[[errno(2)|http://www.freebsd.org/cgi/man.cgi?query=errno&sektion=2]]).
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The
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'''archive_error_string'''()
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returns a textual error message suitable for display.
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'''archive_read_new'''()
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and
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'''archive_write_new'''()
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return pointers to an allocated and initialized
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'''struct archive'''
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object.
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'''archive_read_data'''()
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and
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'''archive_write_data'''()
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return a count of the number of bytes actually read or written.
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A value of zero indicates the end of the data for this entry.
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A negative value indicates an error, in which case the
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'''archive_errno'''()
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and
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'''archive_error_string'''()
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functions can be used to obtain more information.
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== ENVIRONMENT ==
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There are character set conversions within the
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[[ManPagerchiventry3]]
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functions that are impacted by the currently-selected locale.
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== SEE ALSO ==
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[[ManPageBsdtar1]],
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[[ManPagerchiventry3]],
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[[ManPagerchiveead3]],
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[[ManPagerchivetil3]],
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[[ManPagerchiverite3]],
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[[ManPageTar5]]
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== HISTORY ==
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The
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'''libarchive'''
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library first appeared in
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FreeBSD 5.3.
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== AUTHORS ==
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The
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'''libarchive'''
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library was originally written by
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Tim Kientzle <kientzle@acm.org.>
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== BUGS ==
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Some archive formats support information that is not supported by
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'''struct archive_entry .'''
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Such information cannot be fully archived or restored using this library.
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This includes, for example, comments, character sets,
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or the arbitrary key/value pairs that can appear in
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pax interchange format archives.
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Conversely, of course, not all of the information that can be
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stored in an
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'''struct archive_entry'''
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is supported by all formats.
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For example, cpio formats do not support nanosecond timestamps;
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old tar formats do not support large device numbers.
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The ISO9660 reader cannot yet read all ISO9660 images;
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it should learn how to seek.
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The AR writer requires the client program to use
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two passes, unlike all other libarchive writers.
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