Ubuntu Manpage: libarchive — functions for reading and writing streaming archives

Provided by: libarchive-dev_3.7.7-0ubuntu2.3_amd64

NAME

       libarchive — functions for reading and writing streaming archives

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:
• old-style tar archives,
• most variants of the POSIX “ustar” format,
• the POSIX “pax interchange” format,
• GNU-format tar archives,
• most common cpio archive formats,
• 7-Zip archives,
• ar archives (including GNU/SysV and BSD extensions),
• Microsoft CAB archives,
• ISO9660 CD images (including RockRidge and Joliet extensions),
• LHA archives,
• mtree file tree descriptions,
• RAR and most RAR5 archives,
• WARC archives,
• XAR archives,
• Zip archives.
The library automatically detects archives compressed with compress(1), bzip2(1), grzip(1), gzip(1),
lrzip(1), lz4(1), lzip(1), lzop(1), xz(1), or zstd(1) and decompresses them transparently. Decompression
of some formats requires external decompressor utilities. It can similarly detect and decode archives
processed with uuencode(1) or which have an rpm(1) header.

When writing an archive, you can specify the compression to be used and the format to use. The library
can write
• POSIX-standard “ustar” archives,
• POSIX “pax interchange format” archives,
• cpio archives,
• 7-Zip archives,
• ar archives,
• two different variants of shar archives,
• ISO9660 CD images,
• mtree file tree descriptions,
• XAR archives,
• Zip archive.
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 archive_read(3).

WRITING AN ARCHIVE

       See archive_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) supports  for  populating  archive_entry(3)  objects  from  information  in  the
       filesystem.   This  includes  the  information  accessible  from the stat(2) system call as well as ACLs,
       extended attributes, and other metadata.  The  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
       archive_read(3) API.

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.

HISTORY

       The libarchive library first appeared in FreeBSD 5.3.

AUTHORS

       The libarchive library was originally 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 ISO9660 reader cannot yet read all ISO9660 images; it should learn how to seek.

       The AR writer requires the client program to use two passes, unlike all other libarchive writers.

Debian                                           March 18, 2012                                    LIBARCHIVE(3)