gzip

gzip(1) is the GNU compression program. It takes a single file and compresses it. The basic usage is as follows:

   $ gzip infile

The resulting file will be named infile.gz and will usually be smaller than the input file. Note that infile.gz will replace infile. This means that infile will no longer exist, even though a gzipped copy will. Regular text files will compress nicely, while jpeg images, mp3s, and other such files will not compress too well as they are already compressed. This basic usage is a balance of final file size and compression time. The maximum compression can be achieved like so:

   $ gzip -9 infile

This will take a longer time to compress the file, but the result will be as small as gzip can make it. Using lower values for the command line option will cause it to compress faster, but the file will not be as compressed.

Decompressing gzipped files can be done using two commands, which are really just the same program. gzip will decompress any file with a recognized file extension. A recognized extension can be any of the following: .gz, -gz, .z, -z, .Z, or -Z. The first method is to call gunzip(1) on a file, like so:

   $ gunzip infile.gz

This will leave a decompressed version of infile in the current directory, and the .gz extension will be stripped from the filename.

The other way to decompress a gzipped file is to call gzip on the file:

   $ gzip -d infile.gz

This will cause exactly the same behavior as calling gunzip. The reason for this is simple: gunzip is simply a symbolic link to /bin/gzip:

   $ cd /usr/bin
   $ ls -l gunzip
   lrwxrwxrwx   1 root  root  9 Feb  2 09:45 gunzip -> /bin/gzip

So, running gunzip is really just running gzip with a different name. The program can determine how it is being called and take action appropriately. In this case, gzip will know that it is being called as gunzip and decompress the file. Therefore, you can use gzip or gunzip to decompress any gzipped file.