Using the “tar” and “gzip” commands

In UNIX files are packed using the Unix Tape ARchive utility (derived from tape archive and commonly referred to as “tarball”), otherwise are compressed and stored using the GNU zip utilities.

The purpose of this post in not do a detailed and exhaustive description about “tar” and “gzip” commands, but present the essential to use it of an easy way. I hope you enjoy the post!

Basically the “tar”(Tape ARchive) command allows pack/unpack, and the gzip(GNU zip) command compress/uncompress files.

tar

The “tar” command allows us group and ungroup( pack and unpack), a set of files and/or folders into a single file.

To pack some folders and files listed above into a single file, we can run the “tar” command with the following parameters.

tar -cvf application.tar *

tar –cvf application.tar java PERL requirements.txt config.xml

tar -cvf

The parameters of this command can be specified without the hyphen:

tar cvf application.tar java PERL requirements.txt config.xml

Regardless of how the parameters can be referred, below is listed a description of the used parameters:

Option	Meaning	Description
-c	Create	Create a new archive
-v	Verbose	Verbosely list files which are processed
-f	File=ARCHIVE	Use archive file or device

Otherwise the “tar” command can be used to the reverse process: unpack or extract a set of files, directly from the “tar” file:

Option	Meaning	Description
-x	eXtract	Extract files from an archive

Un tar

gzip

This command simply allow to compress a file: any type of file(with the “tar” extension or any other).

To compress a file we can use the following syntax:

gzip

As the “tar” command is used to pack and unpack, the “gzip” command also can be used to compress and uncompress a file.

After the execution of the previous command the result is the file “application.tar.gz”.

In order to perform the decompression can also be used the “gzip” command with the parameter “d”(that means: decompress):

uncompress

To unzip also is usual to use the “gunzip” command:

gunzip myfile.tar.gz

The “tar” also allows compress the “tar” result file, by the “z” option as shown below:

tar cvzf archive_name.tar.gz dirname

The “z”option: compress and pack simultaneously, or simply filters the archive through “gzip”.

tar and gzip

Oftentimes can be confused to understand the meaning of “tar” and “gzip” commands, because they are used together at the same command line through the pipe operator “|”.

Tar and gzip - Extracted from "Wikipedia"

Example 1

tar cvf * | gzip > oracle.tar.gz

The first command(before the pipe) is the “tar”, which pack all files in the current directory.

After this, the ”tar” file is compress :”gzip”(after the pipe) and produce the final file(by the redirection operator “>”) : “oracle.tar.gz”.

Example 2

gunzip < oracle.tar.gz | tar xvf -

In this example the “oracle.tar.gz” file is unzip and the result is a “tar” file that is placed in the “tar” command to unpack. With the hyphen the data resulting from the “gunzip” command is used as input in the tar command.

Useful list

Below you can see a list of very useful actions included these commands:

List the contents of “tar” file

Listing the “tar” archive contents without any extraction(only lists the contents).

tar tvf archive_name.tar

Extract a single file from “tar” file

This syntax allows to extract a single file:”java/MyLib.java” from the ”tar” file.

tar xvf oracle.tar java/MyLib.java

Add a file to an existing ”tar” file

To add a file to an existing “tar” file, only is necessary to use the “r” parameter:

tar rvf oracle.tar conf.cnf

Untar an archive to a different directory

To untar an archive to a different directory, use the following syntax:

tar -zxf oracle.tar.gz -C ora

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