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# Welcome to libarchive!
The libarchive project develops a portable, efficient C library that
can read and write streaming archives in a variety of formats. It
also includes implementations of the common `tar`, `cpio`, and `zcat`
command-line tools that use the libarchive library.
## Questions? Issues?
* http://www.libarchive.org is the home for ongoing
libarchive development, including documentation,
and links to the libarchive mailing lists.
* To report an issue, use the issue tracker at
https://github.com/libarchive/libarchive/issues
* To submit an enhancement to libarchive, please
submit a pull request via GitHub: https://github.com/libarchive/libarchive/pulls
## Contents of the Distribution
This distribution bundle includes the following major components:
* **libarchive**: a library for reading and writing streaming archives
* **tar**: the 'bsdtar' program is a full-featured 'tar' implementation built on libarchive
* **cpio**: the 'bsdcpio' program is a different interface to essentially the same functionality
* **cat**: the 'bsdcat' program is a simple replacement tool for zcat, bzcat, xzcat, and such
* **examples**: Some small example programs that you may find useful.
* **examples/minitar**: a compact sample demonstrating use of libarchive.
* **contrib**: Various items sent to me by third parties; please contact the authors with any questions.
The top-level directory contains the following information files:
* **NEWS** - highlights of recent changes
* **COPYING** - what you can do with this
* **INSTALL** - installation instructions
* **README** - this file
* **CMakeLists.txt** - input for "cmake" build tool, see INSTALL
* **configure** - configuration script, see INSTALL for details. If your copy of the source lacks a `configure` script, you can try to construct it by running the script in `build/autogen.sh` (or use `cmake`).
The following files in the top-level directory are used by the 'configure' script:
* `Makefile.am`, `aclocal.m4`, `configure.ac` - used to build this distribution, only needed by maintainers
* `Makefile.in`, `config.h.in` - templates used by configure script
## Documentation
In addition to the informational articles and documentation
in the online [libarchive Wiki](https://github.com/libarchive/libarchive/wiki),
the distribution also includes a number of manual pages:
* bsdtar.1 explains the use of the bsdtar program
* bsdcpio.1 explains the use of the bsdcpio program
* bsdcat.1 explains the use of the bsdcat program
* libarchive.3 gives an overview of the library as a whole
* archive_read.3, archive_write.3, archive_write_disk.3, and
archive_read_disk.3 provide detailed calling sequences for the read
and write APIs
* archive_entry.3 details the "struct archive_entry" utility class
* archive_internals.3 provides some insight into libarchive's
internal structure and operation.
* libarchive-formats.5 documents the file formats supported by the library
* cpio.5, mtree.5, and tar.5 provide detailed information about these
popular archive formats, including hard-to-find details about
modern cpio and tar variants.
The manual pages above are provided in the 'doc' directory in
a number of different formats.
You should also read the copious comments in `archive.h` and the
source code for the sample programs for more details. Please let us
know about any errors or omissions you find.
## Supported Formats
Currently, the library automatically detects and reads the following fomats:
* Old V7 tar archives
* POSIX ustar
* GNU tar format (including GNU long filenames, long link names, and sparse files)
* Solaris 9 extended tar format (including ACLs)
* POSIX pax interchange format
* POSIX octet-oriented cpio
* SVR4 ASCII cpio
* POSIX octet-oriented cpio
* Binary cpio (big-endian or little-endian)
* ISO9660 CD-ROM images (with optional Rockridge or Joliet extensions)
* ZIP archives (with uncompressed or "deflate" compressed entries, including support for encrypted Zip archives)
* GNU and BSD 'ar' archives
* 'mtree' format
* 7-Zip archives
* Microsoft CAB format
* LHA and LZH archives
* RAR archives (with some limitations due to RAR's proprietary status)
* XAR archives
The library also detects and handles any of the following before evaluating the archive:
* uuencoded files
* files with RPM wrapper
* gzip compression
* bzip2 compression
* compress/LZW compression
* lzma, lzip, and xz compression
* lz4 compression
* lzop compression
The library can create archives in any of the following formats:
* POSIX ustar
* POSIX pax interchange format
* "restricted" pax format, which will create ustar archives except for
entries that require pax extensions (for long filenames, ACLs, etc).
* Old GNU tar format
* Old V7 tar format
* POSIX octet-oriented cpio
* SVR4 "newc" cpio
* shar archives
* ZIP archives (with uncompressed or "deflate" compressed entries)
* GNU and BSD 'ar' archives
* 'mtree' format
* ISO9660 format
* 7-Zip archives
* XAR archives
When creating archives, the result can be filtered with any of the following:
* uuencode
* gzip compression
* bzip2 compression
* compress/LZW compression
* lzma, lzip, and xz compression
* lz4 compression
* lzop compression
## Notes about the Library Design
* This is a heavily stream-oriented system. That means that
it is optimized to read or write the archive in a single
pass from beginning to end. For example, this allows
libarchive to process archives too large to store on disk
by processing them on-the-fly as they are read from or
written to a network or tape drive. Conversely, libarchive
does not support in-place modification or random access.
* The library is designed to be extended with new compression and
archive formats. The only requirement is that the format be
readable or writable as a stream and that each archive entry be
independent. There are articles on the libarchive Wiki explaining
how to extend libarchive.
* On read, compression and format are always detected automatically.
* The same API is used for all formats; in particular, it's very
easy for software using libarchive to transparently handle
any of libarchive's archiving formats.
* Libarchive's automatic support for decompression can be used
without archiving by explicitly selecting the "raw" and "empty"
formats.
* I've attempted to minimize static link pollution. If you don't
explicitly invoke a particular feature (such as support for a
particular compression or format), it won't get pulled in to
statically-linked programs. In particular, if you don't explicitly
enable a particular compression or decompression support, you won't
need to link against the corresponding compression or decompression
libraries. This also reduces the size of statically-linked
binaries in environments where that matters.
* On read, the library accepts whatever blocks you hand it.
Your read callback is free to pass the library a byte at a time
or mmap the entire archive and give it to the library at once.
On write, the library always produces correctly-blocked output.
* The object-style approach allows you to have multiple archive streams
open at once. bsdtar uses this in its "@archive" extension.
* The archive itself is read/written using callback functions.
You can read an archive directly from an in-memory buffer or
write it to a socket, if you wish. There are some utility
functions to provide easy-to-use "open file," etc, capabilities.
* The read/write APIs are designed to allow individual entries
to be read or written to any data source: You can create
a block of data in memory and add it to a tar archive without
first writing a temporary file. You can also read an entry from
an archive and write the data directly to a socket. If you want
to read/write entries to disk, there are convenience functions to
make this especially easy.
* Note: "pax interchange format" is really an extended tar format,
despite what the name says.
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