Richard Dawe > File-ExtAttr-1.09 > File::ExtAttr

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Module Version: 1.09   Source  

NAME ^

File::ExtAttr - Perl extension for accessing extended attributes of files

SYNOPSIS ^

  use File::ExtAttr ':all';
  use IO::File;
  
  # Manipulate the extended attributes of files.
  setfattr('foo.txt', 'colour', 'red') || die;
  my $colour = getfattr('bar.txt', 'colour');
  if (defined($colour))
  {
      print $colour;
      delfattr('bar.txt', 'colour');
  }
  
  # Manipulate the extended attributes of a file via a file handle.
  my $fh = new IO::File('<foo.txt') || die;
  setfattr($fh, 'colour', 'red') || die;
  
  $fh = new IO::File('<bar.txt') || die;
  $colour = getfattr($fh, 'colour');
  if (defined($colour))
  {
      print $colour;
      delfattr($fh, 'colour');
  }

  # List attributes in the default namespace.
  print "Attributes of bar.txt:\n";
  foreach (listfattr($fh))
  {
    print "\t$_\n";
  }

  # Examine attributes in a namespace-aware manner.
  my @namespaces = listfattrns($fh);

  foreach my $ns (@namespaces)
  {
    print "Attributes in namespace '$ns': ";
    my @attrs = listfattr($fh, { namespace => $ns });
    print join(',', @attrs)."\n";
  }

DESCRIPTION ^

File::ExtAttr is a Perl module providing access to the extended attributes of files.

Extended attributes are metadata associated with a file. Examples are access control lists (ACLs) and other security parameters. But users can add their own key=value pairs.

Extended attributes may not be supported by your operating system. This module is aimed at Linux, Unix or Unix-like operating systems (e.g.: Mac OS X, FreeBSD, NetBSD, Solaris).

Extended attributes may also not be supported by your filesystem or require special options to be enabled for a particular filesystem. E.g.:

  mount -o user_xattr /dev/hda1 /some/path

Supported OSes

Linux
Mac OS X
FreeBSD 5.0 and later
NetBSD 4.0 and later
Solaris 10 and later

Unsupported OSes

OpenBSD

Namespaces

Some implementations of extended attributes support namespacing. In those implementations, the attribute is referred to by namespace and attribute name.

Linux

The primary namespaces are user for user programs; security, system and trusted for file security/access-control. See http://www.die.net/doc/linux/man/man5/attr.5.html for more details.

Namespaces on Linux are described by a string, but only certain values are supported by filesystems. In general user, security, system and trusted are supported, by others may be supported -- e.g.: os2 on JFS. File::Extattr will be able to access any of these.

FreeBSD, NetBSD

*BSD have two namespaces: user and system.

Namespaces on *BSD are described by an integer. File::ExtAttr will only be able to access attributes in user and system.

Mac OS X

OS X has no support for namespaces.

Solaris

Solaris has no support for namespaces.

Flags

The functions take a hash reference as their final parameter, which can specify flags to modify the behaviour of the functions. The flags specific to a function are documented in the function's description.

All functions support a namespace flag. E.g.:

  use File::ExtAttr ':all';
  use IO::File;
  
  # Manipulate the extended attributes of files.
  setfattr('foo.txt', 'colour', 'red') || die;
  my $colour = getfattr('bar.txt', 'colour', { namespace => 'user');

If no namespace is specified, the default namespace will be used. On Linux and *BSD the default namespace will be user.

METHODS ^

getfattr([$filename | $filehandle], $attrname, [\%flags])

Return the value of the attribute named $attrname for the file named $filename or referenced by the open filehandle $filehandle (which should be an IO::Handle or subclass thereof).

If no attribute is found, returns undef. Otherwise gives a warning.

setfattr([$filename | $filehandle], $attrname, $attrval, [\%flags])

Set the attribute named $attrname with the value $attrval for the file named $filename or referenced by the open filehandle $filehandle (which should be an IO::Handle or subclass thereof).

%flags allows control of whether the attribute should be created or should replace an existing attribute's value. If the key create is true, setfattr will fail if the attribute already exists. If the key replace is true, setfattr will fail if the attribute does not already exist. If neither is specified, then the attribute will be created (if necessary) or silently replaced.

If the attribute could not be set, a warning is issued.

Note that create cannot be implemented in a race-free manner on *BSD. If your code relies on the create behaviour, it may be insecure on *BSD.

delfattr([$filename | $filehandle], $attrname, [\%flags])

Delete the attribute named $attrname for the file named $filename or referenced by the open filehandle $filehandle (which should be an IO::Handle or subclass thereof).

Returns true on success, otherwise false and a warning is issued.

listfattr([$filename | $filehandle], [\%flags])

Return an array of the attributes on the file named $filename or referenced by the open filehandle $filehandle (which should be an IO::Handle or subclass thereof).

Returns undef on failure and $! will be set.

listfattrns([$filename | $filehandle], [\%flags])

Return an array containing the namespaces of attributes on the file named $filename or referenced by the open filehandle $filehandle (which should be an IO::Handle or subclass thereof).

Returns undef on failure and $! will be set.

EXPORT ^

None by default.

You can request that getfattr, setfattr, delfattr and listfattr be exported using the tag ":all".

Exportable constants

None

BUGS ^

You cannot set empty attributes on Mac OS X 10.4 and earlier. This is a bug in Darwin, rather than File::ExtAttr.

SEE ALSO ^

The latest version of this software should be available from its home page: http://sourceforge.net/projects/file-extattr/

OS2::ExtAttr provides access to extended attributes on OS/2.

Eiciel, http://rofi.pinchito.com/eiciel/, is an access control list (ACL) editor for GNOME; the ACLs are stored in extended attributes.

Various low-level APIs exist for manipulating extended attributes:

Linux

getattr(2), attr(5)

http://www.die.net/doc/linux/man/man2/getxattr.2.html

http://www.die.net/doc/linux/man/man5/attr.5.html

OpenBSD

OpenBSD 3.7 supported extended attributes, although support was never built into the default GENERIC kernel. Its support was documented in the extattr man page:

http://www.openbsd.org/cgi-bin/man.cgi?query=extattr_get_file&apropos=0&sektion=0&manpath=OpenBSD+Current&arch=i386&format=html

Support was removed in OpenBSD 3.8 -- see the CVS history for the include file sys/extattr.h.

http://www.openbsd.org/cgi-bin/cvsweb/src/sys/sys/Attic/extattr.h

FreeBSD

FreeBSD >= 5.0 supports extended attributes.

extattr(2)

http://www.freebsd.org/cgi/man.cgi?query=extattr&sektion=2&apropos=0&manpath=FreeBSD+6.0-RELEASE+and+Ports

NetBSD

NetBSD >= 3.0 supports extended attributes, but you'll need to use NetBSD >= 4.0 to get UFS filesystem support for them.

http://netbsd.gw.com/cgi-bin/man-cgi?extattr_get_file+2+NetBSD-current

http://www.netbsd.org/Changes/changes-4.0.html#ufs

Mac OS X

getxattr(2)

http://developer.apple.com/documentation/Darwin/Reference/ManPages/man2/getxattr.2.html

http://arstechnica.com/reviews/os/macosx-10.4.ars/7

Solaris

attropen(3C), fsattr(5)

http://docsun.cites.uiuc.edu/sun_docs/C/solaris_9/SUNWaman/hman3c/attropen.3c.html

http://docsun.cites.uiuc.edu/sun_docs/C/solaris_9/SUNWaman/hman5/fsattr.5.html

Solaris also has extensible system attributes, which are used by Solaris's CIFS support on ZFS, and have a confusingly similar name to extended file attributes. These system attributes are stored in extended file attributes called SUNWattr_ro and SUNWattr_rw. See PSARC 2007/315 for more details:

http://opensolaris.org/os/community/arc/caselog/2007/315/spec-final-txt/

AUTHOR ^

Kevin M. Goess, <kgoess@ensenda.com>

Richard Dawe, <richdawe@cpan.org>

COPYRIGHT AND LICENSE ^

Copyright (C) 2005 by Kevin M. Goess

Copyright (C) 2005, 2006, 2007, 2008 by Richard Dawe

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.5 or, at your option, any later version of Perl 5 you may have available.

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