Linux-Basics-Complete-Course-With-Notes-Slides

File Compression and Archival

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
```