Decompress files with bunzip2 command in Linux

In this tutorial, we will learn about another Linux/Unix command line tool, bunzip2. It is used compress and decompress files using the Burrows-Wheeler block sorting text compression algorithm, and Huffman coding. The command-line options are deliberately very similar to those of GNU gzip, but they are not identical.

How to install bunzip2 tool?

Debian based - apt install bzip2
Raspbian - apt-get install bzip2
Alpine - apk add bzip2
Arch Linux - pacman -S bzip2
CentOS - yum install bzip2
Fedora - dnf install bzip2
OS X - brew install bzip2
Docker - docker run cmd.cat/bzip2 bzip2

More about bunzip2 command

bunzip2 expects a list of file (which are compressed) names to accompany the command-line flags/options. Each file is replaced by a decompressed version of itself. Each compressed file has the same modification date, permissions, and, when possible, ownership as the corresponding original, so that these properties can be correctly restored at decompression time. File name handling is naive in the sense that there is no mechanism for preserving original file names, permissions, ownerships or dates in file systems which lack these concepts, or have serious file name length restrictions, such as MS-DOS systems.

Files which were not created by bunzip2 will be detected and ignored (based on hex values), and a warning issued. bunzip2 attempts to guess the filename for the decompressed file from that of the compressed file as follows:

filename.bz2 -> filename
filename.bz -> filename
filename.tbz2 -> filename.tar
filename.tbz -> filename.tar
anyothername -> anyothername.out

Notice that if the provided compressed file does not have a file extension (bz2,bz.tbz.tbz2) then the compressed file will get ".out" appended to the original name.

Syntax of bunzip2 command:

bunzip2 [ -fkvsVL ] [ filenames ...  ]
bunzip2 [ -h|--help ]

Options of bunzip2 command:

Examples of bunzip2 command

We will use this file for further examples:

$ echo -e "This is a file containing plain text. \nWe will use this text file for bzip commands explanation" > foo
$
$ cat foo
This is a file containing plain text.
We will use this text file for bunzip2 commands explanation

1. Decompress data with bunzip2 command

One of the most straightforward use cases of the bunzip2 command is to decompress the provided data and write it to a file. Let’s take a look at the two ways to do so:
Read data from a file and write a decompressed form of that data to the same file and also remove .bz2 as extension. i.e, The file named foo.bz2 becomes foo after decompression.

$ ls
foo.bz2
$ bunzip2 foo
$ ls
foo

Read data from standard input (stdin) and decompress the data. So, let us again use bunzip2 to decompress data for a file named bar.

$ cat bar | bunzip2
bunzip2: I won't read compressed data from a terminal.
bunzip2: For help, type: `bunzip2 --help'.

But, If no file names are specified, bunzip2 decompresses from standard input to standard output. In this case, bunzip2 will decline to write decompressed output to a terminal.

$ cat bar | bunzip2 > foo
$ ls
bar  foo
$ cat -A foo
This is a file containing plain text. \nWe will use this text file for bunzip2 commands explanation

Use -dc (or -d -c) options to read data from a file and decompress the data and write to standard output.

$ bunzip2 -zc foo.bz2 > foo
$ ls
foo  foo.bz2

2. Compress data using bunzip2 command

Read data from a file and write a compressed form of that data to the same file and also add .bz2 as extension. i.e, The file named foo becomes foo.bz2 after compression.

$ ls
foo
$ bunzip2 -c foo
$ ls
foo.bz2

Read data from standard input (stdin) and compress the data. So, let us again use bunzip2 to compress data for a file named foo.

$ echo -e "This is a file containing plain text. \nWe will use this text file for bunzip2 commands explanation" | bunzip2 -c
bunzip2: I won't write compressed data to a terminal.
bunzip2: For help, type: `bunzip2 --help'.

But, If no file names are specified, bunzip2 (with -z option) compresses from standard input to standard output. In this case, bunzip2 will decline to write compressed output to a terminal, as this would be entirely incomprehensible and therefore pointless.

$ echo -e "This is a file containing plain text. \nWe will use this text file for bzip commands explanation" | bunzip2 > bar
$ ls
bar  foo
$ cat -A bar
BZh91AY&SYM-QM-^KM-^?V^@^@^IM-SM-^@^@^P@^A^DM-^@?M-gM-^M-P ^@@M-SM"OSM-TM-rM-^^M-!M-dOBM-^@^@^C&F^]g9M-2M-sM-$M-0hM-?^YTV^QM-LM-aM-^J^\^&^KJM-kM-hM-jM-R1M->4+M-^AM-K_M-M-t^D?.lM-tM-\M-^WM-r7^CM-\M-ZM-^DiM-7M-XM-;M-^R)M-BM-^DM-^FM-^L_M-zM-0

Use -zc (or -z -c) options to read data from a file and compress the data and write to standard output.

$ bunzip2 -zc foo > foo.bz2
$ ls
foo  foo.bz2

Conclusion

In this article, we explored the bunzip2 command. This command is used to compress and decompress (default) data. Compression is generally considerably better than that achieved by more conventional LZ77/LZ78-based compressors, and approaches the performance of the PPM family of statistical compressors. It aids in combining the files into one that uses less storage space than the original file did. It uses more memory and has a slower decompression time.