NAME

Archive::Tar::Wrapper - API wrapper around the 'tar' utility

SYNOPSIS

use Archive::Tar::Wrapper;

my $arch = Archive::Tar::Wrapper->new();

# Open a tarball, expand it into a temporary directory
$arch->read("archive.tgz");

# Iterate over all entries in the archive
$arch->list_reset(); # Reset Iterator
# Iterate through archive
while(my $entry = $arch->list_next()) {
    my($tar_path, $phys_path) = @$entry;
    print "$tar_path\n";
}

# Get a huge list with all entries
for my $entry (@{$arch->list_all()}) {
    my($tar_path, $real_path) = @$entry;
    print "Tarpath: $tar_path Tempfile: $real_path\n";
}

# Add a new entry
$arch->add($logic_path, $file_or_stringref);

# Remove an entry
$arch->remove($logic_path);

# Find the physical location of a temporary file
my($tmp_path) = $arch->locate($tar_path);

# Create a tarball
$arch->write($tarfile, $compress);

DESCRIPTION

Archive::Tar::Wrapper is an API wrapper around the 'tar' command line utility. It never stores anything in memory, but works on temporary directory structures on disk instead. It provides a mapping between the logical paths in the tarball and the 'real' files in the temporary directory on disk.

It differs from Archive::Tar in two ways:

• Archive::Tar::Wrapper doesn't hold anything in memory. Everything is stored on disk.
• Archive::Tar::Wrapper is 100% compliant with the platform's tar utility, because it uses it internally.

METHODS

• my $arch = Archive::Tar::Wrapper->new()

  Constructor for the tar wrapper class. Finds the tar executable by searching PATH and returning the first hit. In case you want to use a different tar executable, you can specify it as a parameter:

    my $arch = Archive::Tar::Wrapper->new(tar => '/path/to/tar');
  

  Since Archive::Tar::Wrapper creates temporary directories to store tar data, the location of the temporary directory can be specified:

    my $arch = Archive::Tar::Wrapper->new(tmpdir => '/path/to/tmpdir');
  

  Tremendous performance increases can be achieved if the temporary directory is located on a ram disk. Check the "Using RAM Disks" section below for details.

  Additional options can be passed to the tar command by using the tar_read_options and tar_write_options parameters. Example:

     my $arch = Archive::Tar::Wrapper->new(
                   tar_read_options => "p"
                );
  

  will use tar xfp archive.tgz to extract the tarball instead of just tar xf archive.tgz. Gnu tar supports even more options, these can be passed in via

     my $arch = Archive::Tar::Wrapper->new(
                    tar_gnu_read_options => ["--numeric-owner"],
                );
  

  Similarily, tar_gnu_write_options can be used to provide additional options for Gnu tar implementations. For example, the tar object

    my $tar = Archive::Tar::Wrapper->new(
                  tar_gnu_write_options => ["--exclude=foo"],
              );
  

  will call the tar utility internally like

    tar cf tarfile --exclude=foo ...
  

  when the write method gets called.

  By default, the list_*() functions will return only file entries. Directories will be suppressed. To have list_*() return directories as well, use

     my $arch = Archive::Tar::Wrapper->new(
                   dirs  => 1
                );
  

  If more files are added to a tarball than the command line can handle, Archive::Tar::Wrapper will switch from using the command

    tar cfv tarfile file1 file2 file3 ...
  

  to

    tar cfv tarfile -T filelist
  

  where filelist is a file containing all file to be added. The default for this switch is 512, but it can be changed by setting the parameter max_cmd_line_args:

     my $arch = Archive::Tar::Wrapper->new(
         max_cmd_line_args  => 1024
     );
  

• $arch->read("archive.tgz")

  read() opens the given tarball, expands it into a temporary directory and returns 1 on success und undef on failure. The temporary directory holding the tar data gets cleaned up when $arch goes out of scope.

  read handles both compressed and uncompressed files. To find out if a file is compressed or uncompressed, it tries to guess by extension, then by checking the first couple of bytes in the tarfile.

  If only a limited number of files is needed from a tarball, they can be specified after the tarball name:

    $arch->read("archive.tgz", "path/file.dat", "path/sub/another.txt");
  

  The file names are passed unmodified to the tar command, make sure that the file paths match exactly what's in the tarball, otherwise read() will fail.

• $arch->list_reset()

  Resets the list iterator. To be used before the first call to **$arch-**list_next()>.

• my($tar_path, $phys_path, $type) = $arch->list_next()

  Returns the next item in the tarfile. It returns a list of three scalars: the relative path of the item in the tarfile, the physical path to the unpacked file or directory on disk, and the type of the entry (f=file, d=directory, l=symlink). Note that by default, Archive::Tar::Wrapper won't display directories, unless the dirs parameter is set when running the constructor.

• my $items = $arch->list_all()

  Returns a reference to a (possibly huge) array of items in the tarfile. Each item is a reference to an array, containing two elements: the relative path of the item in the tarfile and the physical path to the unpacked file or directory on disk.

  To iterate over the list, the following construct can be used:

    # Get a huge list with all entries
    for my $entry (@{$arch->list_all()}) {
        my($tar_path, $real_path) = @$entry;
        print "Tarpath: $tar_path Tempfile: $real_path\n";
    }
  

  If the list of items in the tarfile is big, use list_reset() and list_next() instead of list_all.

• $arch->add($logic_path, $file_or_stringref, [$options])

  Add a new file to the tarball. $logic_path is the virtual path of the file within the tarball. $file_or_stringref is either a scalar, in which case it holds the physical path of a file on disk to be transferred (i.e. copied) to the tarball. Or it is a reference to a scalar, in which case its content is interpreted to be the data of the file.

  If no additional parameters are given, permissions and user/group id settings of a file to be added are copied. If you want different settings, specify them in the options hash:

    $arch->add($logic_path, $stringref, 
               { perm => 0755, uid => 123, gid => 10 });
  

  If $file_or_stringref is a reference to a Unicode string, the binmode option has to be set to make sure the string gets written as proper UTF-8 into the tarfile:

    $arch->add($logic_path, $stringref, { binmode => ":utf8" });
  

• $arch->remove($logic_path)

  Removes a file from the tarball. $logic_path is the virtual path of the file within the tarball.

• $arch->locate($logic_path)

  Finds the physical location of a file, specified by $logic_path, which is the virtual path of the file within the tarball. Returns a path to the temporary file Archive::Tar::Wrapper created to manipulate the tarball on disk.

• $arch->write($tarfile, $compress)

  Write out the tarball by tarring up all temporary files and directories and store it in $tarfile on disk. If $compress holds a true value, compression is used.

• $arch->tardir()

  Return the directory the tarball was unpacked in. This is sometimes useful to play dirty tricks on Archive::Tar::Wrapper by mass-manipulating unpacked files before wrapping them back up into the tarball.

• $arch->is_gnu()

  Checks if the tar executable is a GNU tar by running 'tar --version' and parsing the output for "GNU".

Using RAM Disks

On Linux, it's quite easy to create a RAM disk and achieve tremendous speedups while untarring or modifying a tarball. You can either create the RAM disk by hand by running

# mkdir -p /mnt/myramdisk
# mount -t tmpfs -o size=20m tmpfs /mnt/myramdisk

and then feeding the ramdisk as a temporary directory to Archive::Tar::Wrapper, like

my $tar = Archive::Tar::Wrapper->new( tmpdir => '/mnt/myramdisk' );

or using Archive::Tar::Wrapper's built-in option 'ramdisk':

my $tar = Archive::Tar::Wrapper->new( 
    ramdisk => { 
        type => 'tmpfs',
        size => '20m',   # 20 MB
    },
);

Only drawback with the latter option is that creating the RAM disk needs to be performed as root, which often isn't desirable for security reasons. For this reason, Archive::Tar::Wrapper offers a utility functions that mounts the ramdisk and returns the temporary directory it's located in:

# Create new ramdisk (as root):
my $tmpdir = Archive::Tar::Wrapper->ramdisk_mount(
    type => 'tmpfs',
    size => '20m',   # 20 MB
);

# Delete a ramdisk (as root):
Archive::Tar::Wrapper->ramdisk_unmount();

Optionally, the ramdisk_mount() command accepts a tmpdir parameter pointing to a temporary directory for the ramdisk if you wish to set it yourself instead of letting Archive::Tar::Wrapper create it automatically.

KNOWN LIMITATIONS

• Currently, only tar programs supporting the z option (for compressing/decompressing) are supported. Future version will use gzip alternatively.
• Currently, you can't add empty directories to a tarball directly. You could add a temporary file within a directory, and then remove() the file.
• If you delete a file, the empty directories it was located in stay in the tarball. You could try to locate() them and delete them. This will be fixed, though.
• Filenames containing newlines are causing problems with the list iterators. To be fixed.
• If you ask Archive::Tar::Wrapper to add a file to a tarball, it copies it into a temporary directory and then calls the system tar to wrap up that directory into a tarball.

This approach has limitations when it comes to file permissions: if the file to be added belongs to a different user/group, Archive::Tar::Wrapper will adjust the uid/gid/permissions of the target file in the temporary directory to reflect the original file's settings, to make sure the system tar will add it like that to the tarball, just like a regular tar run on the original file would. But this will fail of course if the original file's uid is different from the current user's, unless the script is running with superuser rights.

The tar program by itself (without Archive::Tar::Wrapper) works differently: it'll just make a note of a file's uid/gid/permissions in the tarball (which it can do without superuser rights) and upon extraction, it'll adjust the permissions of newly generated files if the -p option is given (default for superuser).

BUGS

Archive::Tar::Wrapper doesn't currently handle filenames with embedded newlines.

LEGALESE

Copyright 2005 by Mike Schilli, all rights reserved. This program is free software, you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

2005, Mike Schilli cpan@perlmeister.com

MAINTAINER

2018, Alceu Rodrigues de Freitas Junior arfreitas@cpan.org