Linux : Compression and Archiving

Compression is a process or technique to reduce the size of a data file. This is achieved using specific algorithms that identify patterns in the data to reduce its size.

Compression is divided into two types:

• Lossless Compression: Data is compressed without any loss of information. The decompressed data is identical to the original.
• Lossy Compression: Some information is intentionally removed to reduce file size. The decompressed result may not be identical to the original.

Before exploring compression, it is important to understand archiving.

Archiving is the process of collecting multiple files or directories into a single file. This archive can then be compressed using compression tools.

tar is a common archiving tool on Linux. Example usage:

tar -cvf archive.tar file1 file2 directory

In the example above:

• -c

  : Create a new archive

• -v

  : Verbose mode (shows detailed process)

• -f

  : Specifies the archive file name

-z

-j

-J

Common compression tools on Linux:

gzip is a widely used compression utility using the DEFLATE algorithm.

• Compress a file:

    gzip filename
 

  → Produces <code>filename.gz</code>

• Decompress a file:

    gunzip filename.gz
    # or
    gzip -d filename.gz
 

• View compression info:

    gzip -l filename.gz
 

bzip2 uses the Burrows-Wheeler algorithm for better compression than gzip.

• Compress a file:

    bzip2 filename
 

  → Produces <code>filename.bz2</code>

• Decompress a file:

    bunzip2 filename.bz2
    # or
    bzip2 -d filename.bz2
 

• View compression info:

    bzcat filename.bz2 | wc -c
 

xz uses the LZMA (Lempel-Ziv-Markov chain algorithm). It offers higher compression ratios but is slower and more resource-intensive.

• Compress a file:

    xz filename
 

  → Produces <code>filename.xz</code>

• Decompress a file:

    unxz filename.xz
    # or
    xz -d filename.xz
 

• View compression info:

    xz -l filename.xz
 

zip is commonly used to compress and archive multiple files.

• Compress files:

    zip archive.zip file1 file2 folder1
 

• Recursively compress a folder:

    zip -r archive.zip folder1
 

• Add files to existing zip:

    zip -u archive.zip file3
 

• Password-protect a zip:

    zip -r -e archive.zip folder1
 

→ Produces <code>archive.zip</code>

• Decompress:

    unzip archive.zip
 

• View compression info:

    unzip -l archive.zip
 

tar supports built-in compression in one command:

# Compress
tar -czvf archive.tar.gz directory/
# Decompress
tar -xzvf archive.tar.gz

# Compress
tar -cjvf archive.tar.bz2 directory/
# Decompress
tar -xjvf archive.tar.bz2

# Compress
tar -cJvf archive.tar.xz directory/
# Decompress
tar -xJvf archive.tar.xz