Linux tar

导读：
linux中有很多命令可以关于压缩的命令：tar，zip，compress；也有很多的压缩格式，tar，tar.gz,zip。对这些命令和格式有疑惑吗？他们的使用有什么区别呢？

摘要：

• tar是solid compress，rar和7zip也是；而zip不是。
• tar是把文件集合起来，然后用各种方式压缩，如果用gzip便压为tar.gz,如果用bzip2便压缩为tar.bz2。
• 为适用MS-DOS's 8.3 filename limitations，tar.gz equals tgz，tar.bz2 equals tbz。

Details:
    tar files usually have the extension ".tar", as in somefile.tar As a pun, a tar file is commonly referred to as a tarball.[1]
One situation in which you may want to use tar is when you have a number of files which you want send online. If you email the files, you might be sending many attachments. If you post the files on a web page, you might have many links. You can use tar to avoid dealing with multiple files. You create one file, a tar file, into which you put your files. Then you can email this one tar file, or post it on a web page.
    Note that a tar file does not compress the files which it contains. To compress a tar file, you can use a variety of compression programs, such as gzip, bzip2, xz, lzip, lzma, or compress. For example, if you use gzip to compress a tar file, the resulting file might have the name somefile.tar.gz.
    (Alternatively, in the example above, instead of using a compressed tar file, you could put the files into a zip file. Simply, the difference between a zip file and a compressed tar file is that a zip file "compresses each file, and then merges the compressed files," whereas a compressed tar file "merges the files, and then compresses the big file." In other words, a zip file does not use solid compression, but a compressed tar file does.)
    Popular tar programs like the BSD and GNU versions of tar support the command line options -Z (compress), -z (gzip), and -j (bzip2) to automatically compress or decompress the archive file it is currently working with. GNU tar from version 1.20 onwards also supports --lzma (LZMA). 1.21 also supports lzop via --lzop, 1.22 adds support for xz via --xz or -J, and 1.23 adds support for lzip via --lzip.

    Tar archiving is often used together with a compression method, such as gzip, to create a compressed archive. As shown, the combination of the files in the archive are compressed as one unit.
MS-DOS's 8.3 filename limitations, and a desire for brevity, resulted in additional popular conventions for naming compressed tar archives, though this practice has declined with FAT offering long filenames.
.tgz is equivalent to .tar.gz
.tbz, .tbz2 and .tb2 are equivalent to .tar.bz2
.taz is equivalent to .tar.Z
.tlz is equivalent to .tar.lz
.txz is equivalent to .tar.xz

Usage:

tar -cf list.tar /com  # pack the files under /com to list.tar
tar -tf list.tar       # to see the files in the list.tar

references:
http://en.wikipedia.org/wiki/Tar_(file_format)