• Choose a category
• All
• Classic-Fiction

rutabaga$mv garbage.txt.gz rubbish.txt.gz

If we were to gunzip rubbish.txt.gz at this point, the uncompressed file would be named rubbish.txt, after the new (compressed) filename. However, with the -N option, we get the following:

rutabaga$ gunzip -N rubbish.txt.gz

rutabaga$ ls -l garbage.txt

-rw-r--r-- 1 mdw hack 312996 Nov 17 21:44 garbage.txt

gzip and gunzip can also compress or uncompress data from standard input and output. If gzip is given no filenames to compress, it attempts to compress data read from standard input. Likewise, if you use the -c option with gunzip, it writes uncompressed data to standard output. For example, you could pipe the output of a command to gzip to compress the output stream and save it to a file in one step:

rutabaga$ ls -laR $HOME | gzip > filelist.gz

This will produce a recursive directory listing of your home directory and save it in the compressed file filelist.gz. You can display the contents of this file with the command:

rutabaga$ gunzip -c filelist.gz | more

This will uncompress filelist.gz and pipe the output to the more command. When you use gunzip -c, the file on disk remains compressed.

The zcat command is identical to gunzip -c. You can think of this as a version of cat for compressed files. Linux even has a version of the pager less for compressed files, called zless.

When compressing files, you can use one of the options -1 through -9 to specify the speed and quality of the compression used. -1 (also --fast) specifies the fastest method, which compresses the files less compactly, and -9 (also -- --best) uses the slowest, but best compression method. If you don't specify one of these options, the default is -6. None of these options has any bearing on how you use gunzip; gunzip will be able to uncompress the file no matter what speed option you use.

Compared with the more than three decades long history of Unix, gzip is relatively new in the Unix world. The compression programs used on most Unix systems are compress and uncompress, which were included in the original Berkeley versions of Unix. compress and uncompress are very much like gzip and gunzip, respectively; compress saves compressed files as filename.Z as opposed to filename.gz, and uses a slightly less efficient compression algorithm.

However, the free software community has been moving to gzip for several reasons. First of all, gzip works better. Second, there has been a patent dispute over the compression algorithm used by compress—the results of which could prevent third parties from implementing the compress algorithm on their own. Because of this, the Free Software Foundation urged a move to gzip, which at least the Linux community has embraced. gzip has been ported to many architectures, and many others are following suit. Happily, gunzip is able to uncompress the .Z format files produced by compress.

Another compression/decompression program has also emerged to take the lead from gzip. bzip2 is the newest kid on the block and sports even better compression (on the average about 10% to 20% better than gzip), at the expense of longer compression times. You cannot use bunzip2 to uncompress files compressed with gzip and vice versa, and because you cannot expect everybody to have bunzip2 installed on their machine, you might want to confine yourself to gzip for the time being if you want to send the compressed file to somebody else. However, it pays to have bzip2 installed because more and more FTP servers now provide bzip2-compressed packages in order to conserve disk space and bandwidth. It is not unlikely that in a few years from now, gzip will be as uncommon in the Linux world as compress is today. You can recognize bzip2-compressed files by their .bz2 filename extension.

Although the command-line options of bzip2 are not exactly the same as those of gzip, those that have been described in this section are. For more information, see the bzip2(1) manual page.

The bottom line is that you should use gzip/gunzip or bzip2/bunzip2 for your compression needs. If you encounter a file with the