Compression and Encryption: Axis of Evil or Handy Tools?
Putting On the Squeeze: Compressing and Archiving
When you compress a file, you reduce it to a fraction of its original size so you can more efficiently store it or transmit it to another person (compressed files travel faster and take up less space in file libraries). You can't open or execute a compressed file without first decompressing it.
When you smash a bunch of files together into a single file, you're creating an archive. (You don't necessarily compress the files, though.) Archives are useful because they create a package of files that belong together, which makes it easier to distribute a group of related files--for example, the files that make up a program. Because archive files are not always smaller than the sum of their parts, you will sometimes use a compression tool on an archive, resulting in a compressed archive.
Although zip is the most common compression format under DOS and Windows, Unix commonly uses files created with the tar and gzip commands. You'll certainly run into files with names like these:
something.tar An archive file created with tar
something.gz A compressed file created with gzip
something.tar.gz A compressed archive file
something.tgz Same as something.tar.gz
Although the gzip program is built into all Linux systems, it may not be part of some Unix systems, in which case, an older tool called compress is used. Files created by compress have names like this (note the capital "Z"):
something.Z A compressed file
something.tar.Z A compressed tar file
Tip: If you find yourself on a Unix system that doesn't have gzip, you can download the source code (available free) and compile it yourself. See the GNU Project home page at http://www.gnu.org/ to find out how to get the source code.)
The sections that follow show you how to create and undo compressed files and archives.
For more information on the zip command, see the zip manual.
For more information on the gzip command, see the gzip manual.
For more information on the gunzip command, see the gunzip manual.
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