untar(tarfile, files = NULL, list = FALSE, exdir = ".",
compressed = NA, extras = NULL, verbose = FALSE,
restore_times = TRUE, tar = Sys.getenv("TAR"))path.expand) will be performed. Alternatively, a
connection that can be used for binary reads.TRUE, list the files (the equivalent of
tar -tf). Otherwise extract the files (the equivalent of
tar -xf).tar -C). It will be created if necessary."gzip",
"bzip2" and "xz" select that form of compression (and
may be abbreviated to the first letter). TRUE indicates gzip
compression, FALSE no known compression (but an external
tar command may detect compression automagically), and
NA (the default) indicates that the type is inferred from the
file header.NULL or a character string: further command-line
flags such as -p to be passed to an external tar
program.Note that file times in a tarball are stored with a resolution of 1 second, and can only be restored to the resolution supported by the file system (which on a FAT system is 2 seconds).
tar can also contain flags separated from the command by spaces.list = TRUE, a character vector of (relative or absolute)
paths of files contained in the tar archive. Otherwise the return code from system with an external
tar or 0L, invisibly.tar command or for an
internal implementation written in R. The latter is used if
tarfile is a connection or if the argument tar is
"internal" or "" (except on Windows, when
tar.exe is tried first). What options are supported will depend on the tar used.
Modern GNU flavours of tar will support compressed archives,
and since 1.15 are able to detect the type of compression
automatically: version 1.20 added support for lzma and
version 1.22 for xz compression using LZMA2. macOS 10.6 and
later (and FreeBSD and some other OSes) have a tar (also
known as bsdtar) from the libarchive project which
can also detect gzip and bzip2 compression
automatically. For other flavours of tar, environment
variable R_GZIPCMD gives the command to decompress
gzip and compress files, and R_BZIPCMD
for bzip2 files. Arguments compressed, extras and verbose are only
used when an external tar is used. The internal implementation restores symbolic links as links on a
Unix-alike, and as file copies on Windows (which works only for
existing files, not for directories), and hard links as links. If the
linking operation fails (as it may on a FAT file system), a file copy
is tried. Since it uses gzfile to read a file it can
handle files compressed by any of the methods that function can
handle: at least compress, gzip, bzip2
and xz compression, and some types of lzma
compression. It does not guard against restoring absolute file paths,
as some tar implementations do. It will create the parent
directories for directories or files in the archive if necessary. It
handles the standard (USTAR/POSIX), GNU and pax ways of
handling file paths of more than 100 bytes, and the GNU way of
handling link targets of more than 100 bytes. You may see warnings from the internal implementation such
as unsupported entry type 'x'This often indicates an invalid archive: entry types
"A-Z" are
allowed as extensions, but other types are reserved. The only thing
you can do with such an archive is to find a tar program that
handles it, and look carefully at the resulting files. There may also
be the warning using pax extended headersThis is indicates that additional information may have been discarded, such as ACLs, encodings …. The standards only support ASCII filenames (indeed, only alphanumeric plus period, underscore and hyphen).
untar makes no attempt to
map filenames to those acceptable on the current system, and treats
the filenames in the archive as applicable without any re-encoding in
the current locale. The internal implementation does not special-case ‘resource
forks’ in macOS: that system's tar command does. This may
lead to unexpected files with names with prefix ._.tar, unzip.