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

Provided by: libarchive-dev_3.4.0-2ubuntu1.5_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,
• ISO9660 CD images (including RockRidge and Joliet extensions),
• Zip archives,
• ar archives (including GNU/SysV and BSD extensions),
• Microsoft CAB archives,
• LHA archives,
• mtree file tree descriptions,
• RAR archives,
• XAR archives.
The library automatically detects archives compressed with gzip(1), bzip2(1), xz(1), lzip(1), or
compress(1) and decompresses them transparently. 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,
• POSIX octet-oriented cpio archives,
• Zip archive,
• two different variants of shar archives,
• ISO9660 CD images,
• 7-Zip archives,
• ar archives,
• mtree file tree descriptions,
• XAR archives.
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)