02-File-Compression-and-Archival.md

File Compression and Archival

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In this section, we will take a look to compress and archive files

• File Compression and Archival

Viewing file sizes

The du command, which stands for disk usage is a popular command to inspect the size of the file.

• du with -sk shows the size of a file or directory in Kilobytes

  $ du -sk test.img
  

• du with -sh shows the size of a file or directory in human readable format

  $ du -sh test.img
  

• we can also use long list , ls -lh to print the size of the file.

  $ ls -lh test.img
  

Archiving Files

Let us know take a look at widely used utility called tar

• tar is used to group multiple files and directories into a single file. Hence it is specially used for archiving data.
• tar is an abrevation for tape archive.
• Files created with tar are often called tarballs.

To archive a file or directory. Use tar command followed by -c to create an archive and the -f is used to specify the name of the tar file to be created. These is followed by files or directories to be archive.

$ tar -cf test.tar file1 file2 file3 
$ ls -ltr test.tar

The tar command followed by -tf option followed by the tar filename is used to see the contents of the tarball.

$ tar -tf test.tar

The tar command followed by -xf option followed by the tar filename is used to extract the contents from the tarball.

$ tar -xf test.tar

The tar command followed by -zcf option is used to compress the tarball to reduce its size.

$ tar -zcf test.tar

Compression

Compression is the technique used to reduce the size consumed by a file or a dataset.

• To reduce the size of a file or directory in the linux file system, there are commands specificly used for compression.
• Let us now look at the three popular ones

  • bzip2 (.bz2 extension)

  • gzip (.gz extension)

  • xz (.xz extension)

    $ bzip2 test.img
    $ gzip test1.img
    $ xz test2.img
    

The space of the compressed files created by these three commands depends on a few factors, such as the type of data being compressed, the other factors that effect the size are the compression algorithm used by these commands and the compression level used.

• The compressed files can be uncompressed by using the below commands

  • bunzip2

  • gunzip

  • unxz

    $ bunzip2 test.img
    $ gunzip test1.img
    $ unxz test2.img
    

    

Compressed files need not to be uncompressed everytime

• Tools such as zcat , bzcat and xzcat allow the compressed files to be read without an uncompress

  $ zcat hostfile.txt.bz2
  $ zcat hostfile.txt.gz
  $ zcat hostfile.txt.xz