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NAME
erl_tar - Unix 'tar' utility for reading and writing tar archives.
DESCRIPTION
This module archives and extract files to and from a tar file. This module supports
reading most common tar formats, namely v7, STAR, USTAR, and PAX, as well as some of GNU
tar's extensions to the USTAR format (sparse files most notably). It produces tar archives
in USTAR format, unless the files being archived require PAX format due to restrictions in
USTAR (such as unicode metadata, filename length, and more). As such, erl_tar supports tar
archives produced by most all modern tar utilities, and produces tarballs which should be
similarly portable.
By convention, the name of a tar file is to end in ".tar". To abide to the convention, add
".tar" to the name.
Tar files can be created in one operation using function create/2 or create/3.
Alternatively, for more control, use functions open/2, add/3,4, and close/1.
To extract all files from a tar file, use function extract/1. To extract only some files
or to be able to specify some more options, use function extract/2.
To return a list of the files in a tar file, use function table/1 or table/2. To print a
list of files to the Erlang shell, use function t/1 or tt/1.
To convert an error term returned from one of the functions above to a readable message,
use function format_error/1.
UNICODE SUPPORT
If file:native_name_encoding/0 returns utf8, path names are encoded in UTF-8 when creating
tar files, and path names are assumed to be encoded in UTF-8 when extracting tar files.
If file:native_name_encoding/0 returns latin1, no translation of path names is done.
Unicode metadata stored in PAX headers is preserved
OTHER STORAGE MEDIA
The ftp module (Inets) normally accesses the tar file on disk using the file module. When
other needs arise, you can define your own low-level Erlang functions to perform the
writing and reading on the storage media; use function init/3.
An example of this is the SFTP support in ssh_sftp:open_tar/3. This function opens a tar
file on a remote machine using an SFTP channel.
LIMITATIONS
* If you must remain compatible with the USTAR tar format, you must ensure file paths
being stored are less than 255 bytes in total, with a maximum filename component
length of 100 bytes. USTAR uses a header field (prefix) in addition to the name field,
and splits file paths longer than 100 bytes into two parts. This split is done on a
directory boundary, and is done in such a way to make the best use of the space
available in those two fields, but in practice this will often mean that you have less
than 255 bytes for a path. erl_tar will automatically upgrade the format to PAX to
handle longer filenames, so this is only an issue if you need to extract the archive
with an older implementation of erl_tar or tar which does not support PAX. In this
case, the PAX headers will be extracted as regular files, and you will need to apply
them manually.
* Like the above, if you must remain USTAR compatible, you must also ensure than paths
for symbolic/hard links are no more than 100 bytes, otherwise PAX headers will be
used.
EXPORTS
add(TarDescriptor, Filename, Options) -> RetValue
Types:
TarDescriptor = term()
FilenameOrBin = filename()|binary()
NameInArchive = filename()
Filename = filename()|{NameInArchive,FilenameOrBin}
Options = [Option]
Option = dereference|verbose|{chunks,ChunkSize}
ChunkSize = positive_integer()
RetValue = ok|{error,{Filename,Reason}}
Reason = term()
Adds a file to a tar file that has been opened for writing by open/1.
NameInArchive is the name under which the file becomes stored in the tar file. The
file gets this name when it is extracted from the tar file.
Options:
dereference:
By default, symbolic links are stored as symbolic links in the tar file. To
override the default and store the file that the symbolic link points to into
the tar file, use option dereference.
verbose:
Prints an informational message about the added file.
{chunks,ChunkSize}:
Reads data in parts from the file. This is intended for memory-limited machines
that, for example, builds a tar file on a remote machine over SFTP, see
ssh_sftp:open_tar/3.
add(TarDescriptor, FilenameOrBin, NameInArchive, Options) -> RetValue
Types:
TarDescriptor = term()
FilenameOrBin = filename()|binary()
Filename = filename()
NameInArchive = filename()
Options = [Option]
Option = dereference|verbose
RetValue = ok|{error,{Filename,Reason}}
Reason = term()
Adds a file to a tar file that has been opened for writing by open/2. This function
accepts the same options as add/3.
close(TarDescriptor)
Types:
TarDescriptor = term()
Closes a tar file opened by open/2.
create(Name, FileList) ->RetValue
Types:
Name = filename()
FileList = [Filename|{NameInArchive, FilenameOrBin}]
FilenameOrBin = filename()|binary()
Filename = filename()
NameInArchive = filename()
RetValue = ok|{error,{Name,Reason}}
Reason = term()
Creates a tar file and archives the files whose names are specified in FileList
into it. The files can either be read from disk or be specified as binaries.
create(Name, FileList, OptionList)
Types:
Name = filename()
FileList = [Filename|{NameInArchive, FilenameOrBin}]
FilenameOrBin = filename()|binary()
Filename = filename()
NameInArchive = filename()
OptionList = [Option]
Option = compressed|cooked|dereference|verbose
RetValue = ok|{error,{Name,Reason}}
Reason = term()
Creates a tar file and archives the files whose names are specified in FileList
into it. The files can either be read from disk or be specified as binaries.
The options in OptionList modify the defaults as follows:
compressed:
The entire tar file is compressed, as if it has been run through the gzip
program. To abide to the convention that a compressed tar file is to end in
".tar.gz" or ".tgz", add the appropriate extension.
cooked:
By default, function open/2 opens the tar file in raw mode, which is faster but
does not allow a remote (Erlang) file server to be used. Adding cooked to the
mode list overrides the default and opens the tar file without option raw.
dereference:
By default, symbolic links are stored as symbolic links in the tar file. To
override the default and store the file that the symbolic link points to into
the tar file, use option dereference.
verbose:
Prints an informational message about each added file.
extract(Name) -> RetValue
Types:
Name = filename() | {binary,binary()} | {file,Fd}
Fd = file_descriptor()
RetValue = ok|{error,{Name,Reason}}
Reason = term()
Extracts all files from a tar archive.
If argument Name is specified as {binary,Binary}, the contents of the binary is
assumed to be a tar archive.
If argument Name is specified as {file,Fd}, Fd is assumed to be a file descriptor
returned from function file:open/2.
Otherwise, Name is to be a filename.
Note:
Leading slashes in tar member names will be removed before writing the file. That
is, absolute paths will be turned into relative paths. There will be an info
message written to the error logger when paths are changed in this way.
extract(Name, OptionList)
Types:
Name = filename() | {binary,binary()} | {file,Fd}
Fd = file_descriptor()
OptionList = [Option]
Option = {cwd,Cwd}|{files,FileList}|keep_old_files|verbose|memory
Cwd = [dirname()]
FileList = [filename()]
RetValue = ok|MemoryRetValue|{error,{Name,Reason}}
MemoryRetValue = {ok, [{NameInArchive,binary()}]}
NameInArchive = filename()
Reason = term()
Extracts files from a tar archive.
If argument Name is specified as {binary,Binary}, the contents of the binary is
assumed to be a tar archive.
If argument Name is specified as {file,Fd}, Fd is assumed to be a file descriptor
returned from function file:open/2.
Otherwise, Name is to be a filename.
The following options modify the defaults for the extraction as follows:
{cwd,Cwd}:
Files with relative filenames are by default extracted to the current working
directory. With this option, files are instead extracted into directory Cwd.
{files,FileList}:
By default, all files are extracted from the tar file. With this option, only
those files are extracted whose names are included in FileList.
compressed:
With this option, the file is uncompressed while extracting. If the tar file is
not compressed, this option is ignored.
cooked:
By default, function open/2 function opens the tar file in raw mode, which is
faster but does not allow a remote (Erlang) file server to be used. Adding
cooked to the mode list overrides the default and opens the tar file without
option raw.
memory:
Instead of extracting to a directory, this option gives the result as a list of
tuples {Filename, Binary}, where Binary is a binary containing the extracted
data of the file named Filename in the tar file.
keep_old_files:
By default, all existing files with the same name as files in the tar file are
overwritten. With this option, existing files are not overwriten.
verbose:
Prints an informational message for each extracted file.
format_error(Reason) -> string()
Types:
Reason = term()
Cconverts an error reason term to a human-readable error message string.
init(UserPrivate, AccessMode, Fun) -> {ok,TarDescriptor} | {error,Reason}
Types:
UserPrivate = term()
AccessMode = [write] | [read]
Fun when AccessMode is [write] = fun(write, {UserPrivate,DataToWrite})->...;
(position,{UserPrivate,Position})->...; (close, UserPrivate)->... end
Fun when AccessMode is [read] = fun(read2, {UserPrivate,Size})->...;
(position,{UserPrivate,Position})->...; (close, UserPrivate)->... end
TarDescriptor = term()
Reason = term()
The Fun is the definition of what to do when the different storage operations
functions are to be called from the higher tar handling functions (such as add/3,
add/4, and close/1).
The Fun is called when the tar function wants to do a low-level operation, like
writing a block to a file. The Fun is called as Fun(Op,
{UserPrivate,Parameters...}), where Op is the operation name, UserPrivate is the
term passed as the first argument to init/1 and Parameters... are the data added by
the tar function to be passed down to the storage handling function.
Parameter UserPrivate is typically the result of opening a low-level structure like
a file descriptor or an SFTP channel id. The different Fun clauses operate on that
very term.
The following are the fun clauses parameter lists:
(write, {UserPrivate,DataToWrite}):
Writes term DataToWrite using UserPrivate.
(close, UserPrivate):
Closes the access.
(read2, {UserPrivate,Size}):
Reads using UserPrivate but only Size bytes. Notice that there is only an
arity-2 read function, not an arity-1 function.
(position,{UserPrivate,Position}):
Sets the position of UserPrivate as defined for files in file:position/2
Example:
The following is a complete Fun parameter for reading and writing on files using
the file module:
ExampleFun =
fun(write, {Fd,Data}) -> file:write(Fd, Data);
(position, {Fd,Pos}) -> file:position(Fd, Pos);
(read2, {Fd,Size}) -> file:read(Fd, Size);
(close, Fd) -> file:close(Fd)
end
Here Fd was specified to function init/3 as:
{ok,Fd} = file:open(Name, ...).
{ok,TarDesc} = erl_tar:init(Fd, [write], ExampleFun),
TarDesc is then used:
erl_tar:add(TarDesc, SomeValueIwantToAdd, FileNameInTarFile),
...,
erl_tar:close(TarDesc)
When the erl_tar core wants to, for example, write a piece of Data, it would call
ExampleFun(write, {UserPrivate,Data}).
Note:
This example with the file module operations is not necessary to use directly, as
that is what function open/2 in principle does.
Warning:
The TarDescriptor term is not a file descriptor. You are advised not to rely on the
specific contents of this term, as it can change in future Erlang/OTP releases when
more features are added to this module.
open(Name, OpenModeList) -> RetValue
Types:
Name = filename()
OpenModeList = [OpenMode]
Mode = write|compressed|cooked
RetValue = {ok,TarDescriptor}|{error,{Name,Reason}}
TarDescriptor = term()
Reason = term()
Creates a tar file for writing (any existing file with the same name is truncated).
By convention, the name of a tar file is to end in ".tar". To abide to the
convention, add ".tar" to the name.
Except for the write atom, the following atoms can be added to OpenModeList:
compressed:
The entire tar file is compressed, as if it has been run through the gzip
program. To abide to the convention that a compressed tar file is to end in
".tar.gz" or ".tgz", add the appropriate extension.
cooked:
By default, the tar file is opened in raw mode, which is faster but does not
allow a remote (Erlang) file server to be used. Adding cooked to the mode list
overrides the default and opens the tar file without option raw.
To add one file at the time into an opened tar file, use function add/3,4. When you
are finished adding files, use function close/1 to close the tar file.
Warning:
The TarDescriptor term is not a file descriptor. You are advised not to rely on the
specific contents of this term, as it can change in future Erlang/OTP releases when
more features are added to this module..
table(Name) -> RetValue
Types:
Name = filename()|{binary,binary()}|{file,file_descriptor()}
RetValue = {ok,[string()]}|{error,{Name,Reason}}
Reason = term()
Retrieves the names of all files in the tar file Name.
table(Name, Options)
Types:
Name = filename()|{binary,binary()}|{file,file_descriptor()}
Retrieves the names of all files in the tar file Name.
t(Name)
Types:
Name = filename()|{binary,binary()}|{file,file_descriptor()}
Prints the names of all files in the tar file Name to the Erlang shell (similar to
"tar t").
tt(Name)
Types:
Name = filename()|{binary,binary()}|{file,file_descriptor()}
Prints names and information about all files in the tar file Name to the Erlang
shell (similar to "tar tv").