bzip2 Command in Linux
The bzip2 command is a versatile tool you can use for compressing and decompressing files. This command uses the Burrows-Wheeler block sorting text compression algorithm and Huffman coding.
- Burrows-Wheeler Block sorting is a data transformation algorithm that rearranges the data in a way that makes it more compressible.
- On the other hand, Huffman coding is a method of encoding data that reduces the size of the data by using shorter codes for more frequent elements.
Difference between bzip2 and gzip Commands
bzip2 creates smaller archives compared to gzip. This means the files compressed with bzip2 will generally take up less space. Besides that, bzip2 has a slower decompression time compared to gzip. This means it takes longer to extract files from a bzip2 archive.
In addition, bzip2 uses more memory during compression and decompression than gzip and its options are designed to be similar to those of gzip, making it easier for users familiar with gzip to use bzip2. However, they are not exactly the same, so some differences exist.
bzip2 expects a list of file names to be provided along with the command-line flags. Each file you provide is replaced by its compressed version, with the extension .bz2 added to the original file name. The compressed file retains the same modification date, permissions, and ownership as the original file. This ensures that these properties can be restored when the file is decompressed.
bzip2 also does not have mechanisms to preserve original file names, permissions, ownerships, or dates in file systems that lack these concepts or have file name length restrictions (e.g., MS DOS).
Table of Contents
Here is a comprehensive guide to the options available with the bzip2 command −
Syntax of bzip2 Command
The following is the general syntax for the bzip2 command.
bzip2 [OPTIONS] filenames ...
bzip2 Command Options
The following are different options available with the bzip2 command −
| Options | Description |
|---|---|
| -c, --stdout | Compress or decompress to standard output. This means the output will be displayed on the terminal instead of being saved to a file. |
| -d, --decompress | Force decompression. This flag tells bzip2 to decompress the file, regardless of the command used to invoke it. |
| -z, --compress | The complement to -d: forces compression, regardless of the invocation name. |
| -t, --test | Check the integrity of the specified file(s) without decompressing them. It performs a trial decompression and discards the result. |
| -f, --force | Force overwrite of output files. This flag also forces bzip2 to break hard links to files and pass through files without the correct magic header bytes. |
| -k, --keep | Keep (donât delete) input files during compression or decompression. |
| -s, --small | Reduce memory usage during compression, decompression, and testing. -s selects a block size of 200k, which limits memory use to around the same figure, at the expense of your compression ratio. This is useful if your system has limited memory. |
| -q, --quiet | Suppress non-essential warning messages. Messages pertaining to I/O errors and other critical events will not be suppressed. |
| -v, --verbose | Show the compression ratio for each file processed. Further -v's increase the verbosity level, spewing out lots of information which is primarily of interest for diagnostic purposes. |
| -L, --license | Display the software version, license terms, and conditions. |
| -1 (or --fast) to -9 (or -best) | Set the block size to 100 k, 200 k ... 900 k when compressing. The --fast and --best aliases are primarily for GNU gzip compatibility. In particular, --fast doesn't make things significantly faster. And --best merely selects the default behavior. |
| -- | Treats all subsequent arguments as file names, even if they start with a dash. |
| --repetitive-fast, --repetitive-best | These flags are redundant in versions 0.9.5 and above. They were used in earlier versions to control the sorting algorithm. |
Examples of bzip2 Command in Linux
In this section, we'll explore various examples of the bzip2 command using the options we discussed −
- Compress a File and Output to Standard Output
- Decompress a File
- Test the Integrity of a Compressed File
- Force Overwrite of an Existing Compressed File
- Keep the Original File after Compression
- Reduce Memory Usage during Compression
- Suppress Non-essential Warning Messages
- Verbose Mode to Show Compression Ratio
- Compress a File with the Highest Compression Ratio
- Combining and Compressing Files in a Single Command
Compress a File and Output to Standard Output
To compress a filename and save the compressed data to another filename, you can simply use the following command −
bzip2 -c sample1.txt > compressedfile.bz2
The "-c" flag tells bzip2 to write the compressed output to standard output (stdout) instead of replacing the original file.
Decompress a File
To decompress a file that you had already compressed using bzip2, you can use the following syntax −
bzip2 -d sample2.txt.bz2
Test the Integrity of a Compressed File
To test the integrity of a compressed file, you can use the bzip2 command with the "-t" flag:
bzip2 -t sample3.txt.bz2
This command checks if the file is intact and not corrupted. If the file passes the test, there will be no output, indicating that the file has no errors. If there are any issues, an error message will be displayed.
Force Overwrite of an Existing Compressed File
To force the compression of a filename even if a compressed file with the same name already exists, you can use the following syntax −
bzip2 -f sample1.txt
This command compresses sample1.txt and overwrites any existing sample1.txt.bz2.
Keep the Original File after Compression
To compress filename.txt into filename.txt.bz2 while keeping the original filename.txt intact, you can use the following syntax −
bzip2 -k sample4.txt
Reduce Memory Usage during Compression
To reduce memory usage during the compression process, you can simply use the bzip2 command with the "-s" flag −
bzip2 -s sample5.txt
This command is particularly useful if you have a system with limited memory resources, as it makes the compression process less memory-intensive, though it might take a bit longer to complete.
Suppress Non-essential Warning Messages
To suppress non-essential warning messages, you can use the bzip2 command with the "-q" option −
bzip2 -q sample6.txt
This command compresses sample6.txt into sample6.txt.bz2 while keeping the output quiet by not displaying non-essential warnings.
Verbose Mode to Show Compression Ratio
To compress the filename and display detailed information, including the compression ratio, you can use the bzip2 command with the "-v" option −
bzip2 -v my_file1.txt
Compress a File with the Highest Compression Ratio
To compress a file to the maximum compression level, you can use the following command −
bzip2 -9 my_file.txt
Combining and Compressing Files in a Single Command
You can combine a set of MP3 music files into one compressed file using a single command by leveraging tar with the -cjf flags: Here's the single command you can use to combine and compress the MP3 files −
tar -cjf music.tar.bz2 1.mp3 2.mp3 3.mp3
In this command −
- tar creates a new archive.
- -c : stands for "create".
- -j : specifies that the archive should be compressed using bzip2.
- -f : specifies the name of the archive file to create (music.tar.bz2).
- 1.mp3, 2.mp3, and 3.mp3 are the music files being added to the archive.
After running this command, the resulting file music.tar.bz2 contains all the specified MP3 files compressed using bzip2. You can use the cat command to check the contents of the file.
Conclusion
By understanding the bzip2 command and its available options, you can effectively manage file compression tasks to suit your specific needs, whether for reducing file size, preserving file attributes, or handling system limitations.