compress (壓縮文件)

rose1 發表于 2020-08-24 10:28

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命令行 Unix&Linux命令 compress

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在類似Unix的操作系統上，compress命令壓縮文件，使其變得更小。壓縮文件的名稱后綴為.Z。本文檔介紹GNU / Linux版本的compress。

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1 compress 運行系統環境

2 compress 說明

3 compress 語法

4 compress 例子

compress 運行系統環境

Linux

compress 說明

compress實用程序使用自適應Lempel-Ziv 編碼減小文件的大小。每個文件都重命名為同一個名稱加上擴展名。Z. 具有的文件參數。Z擴展將被忽略，除非它將導致錯誤退出后，其他參數處理。如果壓縮不會減小文件的大小，則忽略該文件。

由于許多修改時間、訪問時間、文件標志、文件模式、用戶 ID 和組 ID的權限允許，這些修改時間都保留在新文件中。

如果未指定文件或文件參數是單個破折號（'-'），則標準輸入將壓縮到標準輸出。如果輸入和輸出文件不是常規文件，則不執行減小大小和文件覆蓋的檢查，不刪除輸入文件，并且輸入文件的屬性不會保留在輸出文件中。

壓縮實用程序使用修改后的倫佩爾-齊夫算法。文件中的常見子字符串首先由 9 位代碼 257 及更上版本替換。當達到代碼 512 時，算法切換到 10 位代碼，并繼續使用更多位，直到達到 -b 選項指定的限制或其默認值。

達到限制后，壓縮會定期檢查壓縮比。如果它正在增加，壓縮將繼續使用現有的代碼字典。但是，如果壓縮比降低，壓縮丟棄子字符串表并從頭開始重新生成，這允許算法適應文件的下一個"塊"。

獲得的壓縮量取決于輸入的大小、每個代碼的位數以及公共子字符串的分布。通常，源代碼或英語等文本減少了 50-60%！壓縮通常比赫夫曼編碼（在歷史命令包中使用的）或自適應赫夫曼編碼（歷史命令"緊湊"中使用的）實現的壓縮要好得多，而且計算時間更少。

The compress utility reduces the size of files using adaptive Lempel-Zivcoding. Each file is renamed to the same name plus the extension .Z. A file argument with a .Z extension will be ignored except it will cause an error exit after other arguments are processed. If compression would not reduce the size of a file, the file is ignored.

As many of the modification time, access time, file flags, file mode, user ID, and group ID as allowed by permissions are retained in the new file.

If no files are specified or a file argument is a single dash ('-'), the standard input is compressed to the standard output. If either the input and output files are not regular files, the checks for reduction in size and file overwriting are not performed, the input file is not removed, and the attributes of the input file are not retained in the output file.

The compress utility uses a modified Lempel-Ziv algorithm. Common substrings in the file are first replaced by 9-bit codes 257 and up. When code 512 is reached, the algorithm switches to 10-bit codes and continues to use more bits until the limit specified by the -b option or its default is reached.

After the limit is reached, compress periodically checks the compression ratio. If it is increasing, compress continues to use the existing code dictionary. However, if the compression ratio decreases, compress discards the table of substrings and rebuilds it from scratch, which allows the algorithm to adapt to the next "block" of the file.

The amount of compression obtained depends on the size of the input, the number of bits per code, and the distribution of common substrings. Typically, text such as source code or English is reduced by 50-60%! Compression is generally much better than that achieved by Huffmancoding (as used in the historical command pack), or adaptive Huffman coding (as used in the historical command "compact"), and takes less time to compute.

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compress 語法

compress [-fv] [-b bits] [file ...]

compress -c [-b bits] [file]

選件

-b bits	代碼大小被限制為比特，它必須是在范圍9 .. 16。默認值為16。
-c	壓縮或未壓縮的輸出將寫入標準輸出。沒有文件被修改。該-v選項被忽略。即使結果將大于原始值，也會嘗試進行壓縮。
-f	文件將被覆蓋，而不會提示您進行確認。此外，即使文件實際上沒有減小，文件也將被壓縮。
-v	打印每個文件的減少百分比。如果還使用-c選項，則忽略此選項。

compress [-fv] [-b bits] [file ...]

compress -c [-b bits] [file]

Options

-b bits	The code size is limited to bits, which must be in the range 9..16. The default is 16.
-c	Compressed or uncompressed output is written to the standard output. No files are modified. The -v option is ignored. Compression is attempted even if the results will be larger than the original.
-f	Files are overwritten without prompting for confirmation. Also, files are compressed even if they are not actually reduced in size.
-v	Print the percentage reduction of each file. This option is ignored if the -c option is also used.

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compress 例子

compress -v bigfile.exe

壓縮bigfile.exe并將該文件重命名為bigfile.exe.Z。

compress -v bigfile.exe

Compress bigfile.exe and rename that file to bigfile.exe.Z.

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