Unix commands in Runtime.getRuntime().exec()

[Rishidharan Somu]

String[] cmd = {"/bin/sh", "-c", "cd /usr/local/myfolder/ ; tar -cvf tarball.tar.gz abcd" };
Runtime.getRuntime().exec(cmd);

I am using the above code from inside my java program to create a tar.gz file of the folder abcd which is 10GB in size.

I've never used this command before and would like to know if it is advisable to use it.

[Jeff Verdegan]

Runtime.exec() is fine, but the suggested replacement is ProcessBuilder. A lot of people still use exec() though, and I think it just calls PB under the hood.

[Paul Clapham]

I believe the "tar" command is very commonly used in Unix, so I don't see any reason not to use it.

[Rob Spoor]

I would actually stop using an external process, and switch to using Java code. Apache Commons Compress has a class TarArchiveOutputStream which works similar to ZipOutputStream. Wrap a GZIPOutputStream in it, and simply add entries recursively using File.listFiles():

TarArchiveOutputStream out = new TarArchiveOutputStream(new GZIPOutputStream(new FileOutputStream("/usr/local/myfolder/tarball.tar.gz")));
tarFolder(out, new File("/usr/local/myfolder/abcd"), "");
...
private void tarFolder(TarArchiveOutputStream out, File folder, String path)
{
    ...
}

I've added that parameter path because in a recursive call, you need to append the folder to it. This is the only way I've found to maintain the full path of the Tar entries. For example, the following could be a recursive call chain:
tarFolder(out, new File("/usr/local/myfolder/abcd"), ""); -- to tar the /usr/local/myfolder/abcd folder.
tarFolder(out, subFolder, "efgh"); -- to tar sub folder efgh where subFolder represents this sub folder.
tarFolder(out, subFolder, "efgh/ijkl"); -- to tar sub folder ijkl of folder efgh where subFolder represents this sub folder.
pseudo code: tarFile(out, file, "efgh/ijkl/file.ext"); -- to tar file file.ext inside folder ijkl] where [tt]file represents this file.


If you continue with Runtime.exec or ProcessBuilder, you should have read When Runtime.exec() won't first.