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man : OpenBSD::Ustar(3p)
OpenBSD::Ustar(3pPerl Programmers Reference GuiOpenBSD::Ustar(3p)
NAME
OpenBSD::Ustar - simple access to Ustar tar(1) archives
SYNOPSIS
use OpenBSD::Ustar;
# for reading
open(my $in, "<", $arcnameforreading) or die;
$rdarc = OpenBSD::Ustar->new($in, $destdir);
while (my $o = $rdarc->next()) {
# decide whether we want to extract it, change object attributes
$o->create();
}
$rdarc->close();
# for writing
open(my $out, ">", $arcnameforwriting) or die;
$wrarc = OpenBSD::Ustar->new($fh, $destdir);
# loop
my $o = $wrarc->prepare($filename);
# tweak some entry parameters
$o->write();
$wrarc->close();
# for copying
open(my $in, "<", $arcnameforreading) or die;
$rdarc = OpenBSD::Ustar->new($in, $destdir);
open(my $out, ">", $arcnameforwriting) or die;
$wrarc = OpenBSD::Ustar->new($fh, $destdir);
while (my $o = $rdarc->next()) {
$o->copy($wrarc);
}
$rdarc->close();
$wrarc->close();
DESCRIPTION
"OpenBSD::Ustar" provides an API to read, write and copy
archives compatible with tar(1). For the time being, it
can only handle the USTAR archive format.
A filehandle $fh is associated with an "OpenBSD::Ustar"
object through "new". For archive reading, the filehandle
should support "read". "OpenBSD::Ustar" does not rely on
"seek" or "rewind" in order to be usable on pipe outputs.
For archive writing, the filehandle should support
"print".
Note that read and write support are mutually exclusive,
though there is no need to specify the mode used at
creation time; it is implicitly provided by the underlying
filehandle.
Read access to an archive object $rdarc occurs through a
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loop that repeatedly calls "$o = $rdarc->next()" to obtain
the next archive entry. It returns an archive entry
object $o that can be queried to decide whether to extract
this entry or not.
Write access to an archive object $wrarc occurs through a
user-directed loop: obtain an archive entry through "$o =
$wrarc->prepare($filename)", which can be tweaked manually
and then written to the archive.
Most client software will specialize "OpenBSD::Ustar" to
their own needs. Note however that "OpenBSD::Ustar" is
not designed for inheritance. Composition (putting a
"OpenBSD::Ustar" object inside your class) and forwarding
methods (writing "create" or "next" methods that call the
corresponding "OpenBSD::Ustar" method) are the correct way
to use this API.
Note that "OpenBSD::Ustar" does not do any caching. The
client code is responsible for retrieving and storing
archives if it needs to scan through them multiple times
in a row.
Actual extraction is performed through "$o->extract()" and
is not mandatory. Thus, client code can control whether it
wants to extract archive elements or not.
Small files can also be directly extracted to a scalar
using "$v = $o->contents()".
Actual writing is performed through "$o->write()" and is
not mandatory either.
Archives should be closed using "$wrarc->close()", which
will pad the archive as needed and close the underlying
file handle. In particular, this is mandatory for write
access, since valid archives require blank-filled blocks.
This is equivalent to calling "$wrarc->pad()", which will
complete the archive with blank-filled blocks, then
closing the associated file handle manually.
Client code may decide to abort archive extraction early,
or to run it through until "$arc->next()" returns false.
The "OpenBSD::Ustar" object doesn't hold any hidden
resources and doesn't need any specific clean-up.
Client code is only responsible for closing the underlying
filehandle and terminating any associated pipe process.
An object $o returned through "next" or through "prepare"
holds all the characteristics of the archive header:
"$o->IsDir()" true if archive entry is a directory
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"$o->IsFile()" true if archive entry is a file
"$o->IsLink()" true if archive entry is any kind of
link
"$o->IsSymLink()" true if archive entry is a symbolic
link
"$o->IsHardLink()" true if archive entry is a hard link
"$o->{name}" filename
"$o->{mode}" chmod(2) mode
"$o->{mtime}" utime(2) modification time
"$o->{uid}" owner user ID
"$o->{gid}" owner group ID
"$o->{uname}" owner user name
"$o->{gname}" owner group name
"$o->{linkname}" name of the source link, if applicable
The fields "name", "mode", "mtime", "uid", "gid" and
"linkname" can be altered before calling "$o->create()" or
"$o->write()", and will properly influence the resulting
file.
The relationship between "uid" and "uname", and "gid" and
"gname" conforms to the USTAR format usual behavior.
In addition, client code may define "$o->{cwd}" in a way
similar to tar(1)'s "-C" option to affect the creation of
hard links.
All creation commands happen relative to the current
destdir of the $arc "OpenBSD::Ustar" object. This is set
at creation, and can later be changed through
"$arc->destdir($value)".
During writing, hard link status is determined according
to already written archive entries: a name that references
a file which has already been written will be granted hard
link status.
Hard links can not be copied from one archive to another
unless the original file has also been copied. Calling
"$o->alias($arc, $name)" will trick the destination
archive $arc into believing $o has been copied under the
given $name, so that further hard links will be copied
over.
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Archives can be copied by creating separate archives for
reading and writing. Calling "$o = $rdarc->next()" and
"$o->copy($wrarc)" will copy an entry obtained from $rdarc
to $wrarc.
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