RFR: 8173970: jar tool should have a way to extract to a directory

Lance Andersen lance.andersen at oracle.com
Wed Mar 3 15:44:32 UTC 2021

Hi Jaikiran,

It should not be too difficult to support the options listed below via GNUStyleOptions.

Some other things needed to be defined and agreed upon in order to move forward

  *   The behavior if the path does not exist
  *   If the option is specified more than once on the command line
  *   Clarify the behavior if any of the files exist in the specified target directory.

Once you have a chance to consider the above, please send your proposal back to the alias to continue the discussion


On Mar 3, 2021, at 5:14 AM, Jaikiran Pai <jai.forums2013 at gmail.com<mailto:jai.forums2013 at gmail.com>> wrote:

Thank you Lance. So I think there's some level of agreement on using -C and --dir (or --directory) for the option names.

Anymore opinion on the directory creation semantics and any other aspects to consider?


On 28/02/21 5:38 pm, Lance Andersen wrote:
Hi Jaikiran,

Thank you for this.  I went through this myself yesterday in addition to what you have below here are a few more:

7zip:       -o
Info-zip:  -d  (MacOS version of zip)
Bandzip: -o:{dir}
jpackage: -d —dest
jlink —output

Thinking about this some more, I might suggest supporting



On Feb 27, 2021, at 11:19 PM, Jaikiran Pai <jai.forums2013 at gmail.com<mailto:jai.forums2013 at gmail.com>> wrote:

Hello Alan,

On 27/02/21 2:23 pm, Alan Bateman wrote:

Yes, the option name will need to be agreed. It would be useful to enumerate the options that the other tools are using to specify the location where to extract. If you see JBS issues mentioning tar -C not supporting chdir when extracting then it might be Solaris tar, which isn't the same as GNU tar which has different options. It might be better to look at more main stream tools, like unzip although jar -d is already taken. It would be nice if there were some consistency with other tools in the JDK that doing extracting (The jmod and jimage extract commands use use --dir for example).

I had a look at both tar and unzip commands on MacOS and Linux (CentOS) setup that I had access to.

tar on MacOS:

tar --version
bsdtar 3.3.2 - libarchive 3.3.2 zlib/1.2.11 liblzma/5.0.5 bz2lib/1.0.6

The version of this tool has:

-C directory, --cd directory, --directory directory
             In c and r mode, this changes the directory before adding the following files.
             In x mode, change directories after opening the archive but before extracting
             entries from the archive.

A command like "tar -xzf foo.tar.gz -C /tmp/bar/" works fine and extracts the foo.tar.gz from current directory to a target directory /tmp/bar/

tar on CentOS:

tar --version
tar (GNU tar) 1.26

This version of the tool has:

Common options:
       -C, --directory=DIR
              change to directory DIR

Although the wording isn't clear that, when used with -x, it extracts to the directory specified in -C, it does indeed behave that way.

Specifically, a command like "tar -xzf foo.tar.gz -C /tmp/bar/" works fine and extracts the foo.tar.gz from current directory to a target directory /tmp/bar/

unzip on both MacOS and CentOS:

unzip -v
UnZip 6.00 of 20 April 2009, by Info-ZIP.  Maintained by C. Spieler.

This version of the tool has:

[-d exdir]
              An optional directory to which to extract files.  By default, all files and sub-
              directories are recreated in the current directory; the -d option allows extrac-
              tion in an arbitrary directory (always assuming one has permission to  write  to
              the  directory).  This option need not appear at the end of the command line; it
              is also accepted before the zipfile specification (with  the  normal  options),
              immediately  after  the zipfile specification, or between the file(s) and the -x
              option.  The option and directory may be concatenated without  any  white  space
              between  them,  but  note  that  this may cause normal shell behavior to be sup-
              pressed.  In particular, ``-d ~'' (tilde) is expanded by Unix C shells into  the
              name of the user's home directory, but ``-d~'' is treated as a literal subdirec-
              tory ``~'' of the current directory.

unzip foo.zip -d /tmp/bar/ works fine and extracts the foo.zip from current directory to /tmp/bar/

jimage and jmod

The jimage and jmod as you note use the --dir option for extracting to that specified directory.

Those were the tools I looked at. I think using the -d option with -x for the jar command is ruled out since it already is used for a different purpose, although for a different "main" operation of the jar command.

As for using --dir for this new feature, I don't think it alone will be enough. Specifically, I couldn't find a "short form" option for the --dir option in the jimage or jmod commands. For the jar extract feature that we are discussing here, I think having a short form option (in addition to the longer form) is necessary to have it match the usage expectations of similar other options that the jar command exposes. So even if we do choose --dir as the long form option, we would still need a short form for it and since -d is already taken for something else, we would still need to come up with a different one. The short form of this option could be -C (see below).

I think reusing the -C option, for this new feature, perhaps is a good thing. The -C is currently used by the update and create "main" operation of the jar command and the man page for this option states:

-C dir
              When creating (c) or updating (u) a JAR file, this option temporarily changes
              the directory while processing files specified by the file operands. Its
              operation is intended to be similar to the -C option of the UNIX tar utility.For
              example, the following command changes to the classes directory and adds the
              Bar.class file from that directory to my.jar:

              jar uf my.jar -C classes Bar.class

Using the -C option would indeed align it with the tar command. For the "long form" of this option, the tar command (both on MacOS and CentOS) uses --directory. For this jar extract feature though, we could perhaps just use --dir to have it align with the jimage and the jmod tools.

So I think the combination of -C (short form) and --dir (long form) would perhaps be suitable for this feature.

There are other discussion points around the behavior when the target directory exists or does not exist, to ensure there is some consistency with main stream tools.

I'm guessing you mean the behaviour of creating a directory (or a hierarchy of directories) if the target directory is not present? My testing with the tar tool (both on MacOS and CentOS) shows that if the specified target directory doesn't exist, then the extract fails. The tar extract command doesn't create the target directory during extract. On the other hand, the unzip tool, does create the directory if it doesn't exist. However, interestingly, the unzip tool creates only one level of that directory if it doesn't exist. Specifically, if you specify:

unzip foo.zip -d /tmp/blah/

and if "blah/" isn't a directory inside /tmp/ directory, then it creates the "blah/" directory inside /tmp/ and then extracts the contents of the zip into it.


unzip foo.zip -d /tmp/blah/hello/

and if "blah/" isn't a directory inside /tmp/ directory, then this command fails with an error and it doesn't create the hierarchy of the target directories.

Coming to the jimage and the jmod commands, both these commands create the entire directory hierarchy if the target directory specified during extract, using --dir, doesn't exist. So a command like:

jimage extract --dir /tmp/blah/foo/bar/ jdkmodules

will create the blah/foo/bar/ directory hierarchy if blah doesn't exist in /tmp/, while extracting the "jdkmodules" image.

From the user point of view, I think this behaviour of creating the directories if the target directory doesn't exist, is probably the most intuitive and useful and if we did decide to use this approach for this new option for jar extract command, then it would align with what we already do in jimage and jmod commands.

One another minor detail, while we are at this, is that, IMO we should let the jar extract command to continue to behave the way it currently does when it comes to overwriting existing files. If the jar being extracted contains a file by the same name, in the target directory (hierarchy) then it should continue to overwrite that file. In other words, I don't think we should change the way the jar extract command currently behaves where it overwrites existing files when extracting.



Lance Andersen| Principal Member of Technical Staff | +1.781.442.2037
Oracle Java Engineering
1 Network Drive
Burlington, MA 01803
Lance.Andersen at oracle.com<mailto:Lance.Andersen at oracle.com>

[cid:E1C4E2F0-ECD0-4C9D-ADB4-B16CA7BCB7FC at home]

Lance Andersen| Principal Member of Technical Staff | +1.781.442.2037
Oracle Java Engineering
1 Network Drive
Burlington, MA 01803
Lance.Andersen at oracle.com<mailto:Lance.Andersen at oracle.com>

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