Compression and Archiving
July 19, 1998
Before we conclude this tutorial, there is
one final subject that you should know about. This is compression/
archiving. UNIX provides several good tools for compressing and
archiving your files so that you can create backups of important
files or so that you can easily transfer large directory structures
from one site to another. Though there are several good utilities for
these purposes, two utilities have become the standard for web
developers; partly because of their functionality and partly because
they work cross-platform. That is, what is compressed and archived
on unix can be decompressed and de-archived on Windows or Mac using
such applications as
WinZip or
MacTar.
We'll look at the tar utility first.
The tar utility is used to archive an entire directory structure
into a single file. This single file will contain all of the
information in all of the directories. A tar file is easily moved
from one site to another because it is a single file. when the
tar file gets to the new location, you can un archive the whole
thing and the directory structure will be recreated in the new
location. The tar command is executed as follows:
tar [key] [argument] [drive] [options] file_list
Tar has several options. The ones you probably will use
are shown below.
| Option |
Explanation |
| key |
Specifies the action to take. Keys will be one of the following:
c = creates a new archive or overwrites an existing one
r = appends the files in the file_list to the end of an existing
archive.
t = lists the contents of the archive
u = updates the archive with the latest copies of files within
the archive.
x = extracts the files from the archive.
|
| argument |
For your uses you will rarely need the argument but it is here
if you do. |
| drive |
You will never need this option as a web technician. This is
mainly used for sysadmins making global backups |
| f |
An option that specifies the name to be used for the archive. |
| A |
Makes all absolute file names into relative filenames. |
| v |
Tells tar to report in verbose mode about its activities. |
| w |
Tells tar to query you for a "y" or "n" as it takes actions. |
Let's look at an example:
![[tar]](Images/tar.gif)
"Compress" and "uncompress", on the other hand, are
common utilities used for compressing files. They are particularly
useful when used in combination with tar because once you tar an
archive, you can compress the tar file which makes it much more
portable (perhaps via ftp).
Take a look at the following example
in which we use compress to shrink a TAR file:
Manipulating your Environment
Introduction to UNIX for Web Developers | Table of Contents
|
