functions for reading and writing streaming
library provides a flexible
interface for reading and writing archives in various formats such as tar and
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
and decompresses them transparently. It can similarly detect and decode
archives processed with
or which have an
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
implementations on many systems as well as several newer implementations of
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
() functions and the
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.
API allows you to write
objects to disk using the same API used by
API is used internally by
(); 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.
supports for populating
objects from information in the filesystem. This includes the information
accessible from the
system call as well as ACLs, extended attributes, and other metadata. The
API also supports iterating over directory trees, which allows directories of
files to be read using an API compatible with the
Detailed descriptions of each function are provided by the corresponding manual
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
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
Most functions return
success, non-zero on error. The return value indicates the general severity of
the error, ranging from
indicates a minor problem that should probably be reported to the user, to
, which indicates a serious
problem that will prevent any further operations on this archive. On error,
() function can be used to
retrieve a numeric error code (see
() returns a
textual error message suitable for display.
() return pointers to an
allocated and initialized struct archive object.
() 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
() functions can be
used to obtain more information.
There are character set conversions within the
functions that are impacted by the currently-selected locale.
library first appeared in
library was originally written
by Tim Kientzle
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
The ISO9660 reader cannot yet read all ISO9660 images; it should learn how to
The AR writer requires the client program to use two passes, unlike all other