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Today, I will talk to you about how to use Bzip2 compressed files in the Linux system, many people may not know much about it. In order to make you understand better, the editor has summarized the following contents for you. I hope you can get something according to this article.

Install Bzip2

The command is as follows:

Make-f Makefile-libbz2_so & &

Make & &

Make install & &

Cp bzip2-shared / bin/bzip2 & &

Ln-s libbz2.so.1.0 libbz2.so & &

Cp-a libbz2.so* / lib & &

Rm / lib/libbz2.so & &

Ln-s. /.. / lib/libbz2.so.1.0 / usr/lib/libbz2.so & &

Rm / usr/bin/ {bunzip2,bzcat,bzip2} & &

Mv / usr/bin/ {bzip2recover,bzless,bzmore} / bin & &

Ln-s bzip2 / bin/bunzip2 & &

Ln-s bzip2 / bin/bzcat

Although not a required part, it is worth mentioning that there is a patch for the Tar package that makes it easier for tar programs to compress and decompress with bzip2/bunzip2. If it's pure tar, you have to use commands like bzcat file.tar.bz | tar-xv or tar-- use-compress-prog=bunzip2-xvf file.tar.bz2 to use bzip2 and bunzip2. This patch provides the-j option, and you can use the command: tar-xvfj file.tar.bz2 to extract a package in bzip2 format. Applying this patch will be mentioned later when you install the Tar package.

Brief introduction

Bzip2, bunzip2-A block sort file compression software, v0.9.5

Bzcat-extract the file to standard output

Bzip2recover-recover corrupted bzip2 files

Bzip2 uses Burrows-Wheeler block sorting text compression algorithm and Huffman encoding to compress files. The compression ratio is generally much better than that of LZ77/LZ78-based compression software, and its performance is close to that of PPM statistical compression software.

The command-line arguments are intentionally designed to be very close to GNU gzip, but not exactly the same.

Bzip2 reads the file name and parameters from the command line. Each file is replaced by a compressed file named "original file name .bz2". Each compressed file has the same modification time, permissions, and, if possible, the same owner, so these features will be restored correctly when unzipped. In some file systems, there is no concept of permissions, ownership, or time, or there are strict restrictions on the length of file names, such as MSDOS. In this case, bzip2 has no mechanism to maintain the original file name, ownership, permissions, and time. In this sense, bzip2's handling of file names is naive.

Bzip2 and bunzip2 do not overwrite existing files by default. If you want to overwrite an existing file, specify the-f option.

If no filename is specified, bzip2 compresses the data from standard input and writes it to standard output. In this case, bzip2 refuses to write the compression result to the terminal because it is completely incomprehensible and meaningless.

Bunzip2 (and bzip2-d) decompresses all specified files. Files that are not generated by bzip2 will be ignored with a warning message. Bzip2 determines the decompressed file name from the compressed file name in the following ways:

Decompress filename.bz2 into filename

Decompress filename.bz into filename

Decompress filename.tbz2 into filename.tar

Decompress filename.tbz into filename.tar

Decompress anyothername into anyothername.out

If the suffix of the file name is not one of the following: .bz2, .bz, .tbz2 or .tbz, .bzip2 complains that the original file name cannot be determined and uses the original file name plus .out as the unzipped file name.

During compression, if you do not provide a file name, bzip2 will read the data from the standard input and write the compression result to the standard output.

Bunzip2 can correctly extract files that are joined by two or more compressed files. The result of the decompression is the corresponding uncompressed files connected together.

Bzip2 also supports integrity checking of conjoined compressed files (the-t option).

You can also use the-c option to compress or extract files to standard output. Multiple files can be compressed or decompressed in this way. The output results are sent to standard output in turn. Compressing multiple files in this way generates a data stream containing multiple compressed files. Such data streams can only be decompressed correctly by version 0.9.0 or subsequent versions of bzip2. Earlier versions of bzip2 will stop after unzipping the first file.

Bzcat (or bzip2-dc) unzips all specified files to standard output.

Bzip2 reads the parameters in turn from the environment variables BZIP2 and BZIP and processes them before the command line arguments. This is a convenient way to provide default options.

Even if the compressed file is slightly larger than the original file, the compression is always the same. Files smaller than about 100 bytes tend to become larger after compression because there is a 50-byte header. For random data (including the output of most compressed software), each byte is compressed to about 8.05 bits, and the magnification is about 0.5%.

Bzip2 uses a 32-bit CRC check code to verify that the decompressed file is the same as the original file. This can be used to detect whether the compressed file is corrupted and to prevent unknown defects in bzip2 (which, with luck, is highly unlikely). The chance of data corruption going undetected is very small, about 1/4000000000 for each file being processed. The check is done during unzipping, so it can only indicate that something is wrong. It can help recover the original uncompressed data. You can use bzip2recover to try to recover data from corrupted files.

Return value: 0 for normal exit, 1 for environmental problems (file not found, illegal options, Icano error, etc.), 2 indicates that the compressed file is corrupted, and 3 is returned for internal consistency errors (such as defects) that lead to bzip2 emergency exit.

Parameters.

-c-- stdout

Compress or decompress data to standard output.

-d-- decompress

Force decompression. Bzip2, bunzip2, and bzcat are actually the same program, and what to do will be determined by the program name. When this option is specified, this mechanism is ignored and bzip2 is forced to decompress.

-z-- compress

A supplement to the-d option: forces a compression operation, regardless of which program is executed.

-t-- test

Checks the integrity of the specified file, but does not extract it. The data will actually be experimentally decompressed without outputting the results.

-f-- force

Force to overwrite the output file. Usually bzip2 does not overwrite files that already exist. This option also forces bzip2 to break the hard connection of the file, which bzip2 does not do by default.

-k-- keep

Keep the input files when you compress or extract them (do not delete them).

-s-- small

Reduce memory usage when compressing, decompressing, and checking. Using a modified algorithm for compression and testing, each data block requires only 2.5 bytes. This means that any file can be unzipped in 2300k of memory, albeit at half the usual speed.

In compression,-s will select a block length of 200k, and the amount of memory will be limited to about 200k, at the cost of reducing the compression ratio. In summary, if the machine has less memory (8 megabytes or less), you can use the-s option for all operations. See memory management below.

-Q-- quiet

Suppress unimportant warnings. Messages related to Icano errors and other serious events will not be suppressed.

-v-- verbose

Detailed mode-displays the compression ratio of each file being processed. More-v options on the command line will increase the level of detail so that bzip2 displays a lot of information that is used primarily for diagnostic purposes.

-L-- license-V-- version

Displays the software version, license terms and conditions.

-1 to-9

The block length is set to 100k and 200k during compression. 900 k . It has no effect on decompression. See memory management below.

--

Think of all subsequent command-line variables as file names, even if they start with a minus sign "-". You can use this option to handle file names that begin with the minus sign "-", for example: bzip2-myfilename.

-repetitive-fast-repetitive-best

These options are redundant in 0.9.5 and above. In earlier versions, these two options provided some rough control over the behavior of the sorting algorithm, which was useful in some cases. Version 0.9.5 and above uses improved algorithms independent of these options.

Example:

Example a, compression

The code is as follows:

[root@localhost ~] # bzip2-z abc.sh # Compression

The code is as follows:

[root@localhost ~] # bzip2-kv abc.sh # compressed original text retention

Abc.sh: 1.220 saved 1, 6.557 bits/byte, 18.04% saved, 255 in, 209 out.

The code is as follows:

[root@localhost] # bzip2-9-c abc.sh > abc.bz2 # compress original text retention

Example b, decompression

The code is as follows:

Root@tnak-VirtualBox:/home/tnak# bzip2-dv abc.sh.bz2

Abc.sh.bz2: done

After reading the above, do you have any further understanding of how to use Bzip2 compressed files in the Linux system? If you want to know more knowledge or related content, please follow the industry information channel, thank you for your support.

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