tar

Understanding tar

tar (short for “tape archiver”) is a powerful command-line utility used for creating archive files. An archive combines multiple files and directories into a single file, often compressed for smaller storage size and easier transfer. tar itself doesn’t perform compression; it relies on external compression tools like gzip, bzip2, or xz.

Basic tar Operations

The basic syntax of tar is:

tar [options] [archive-file] [file-list]

Let’s look at some common options:

• -c (create): Creates a new archive.
• -x (extract): Extracts files from an archive.
• -t (list): Lists the contents of an archive without extracting.
• -v (verbose): Displays detailed information during the process.
• -f (file): Specifies the archive file name.
• -z (gzip): Compresses the archive using gzip.
• -j (bzip2): Compresses the archive using bzip2.
• -J (xz): Compresses the archive using xz.

Creating Archives

Let’s create an archive named my_archive.tar.gz containing the files file1.txt, file2.txt, and the directory my_directory:

mkdir my_directory
touch my_directory/file3.txt
touch file1.txt
touch file2.txt

tar -czvf my_archive.tar.gz file1.txt file2.txt my_directory

This command uses:

• -c: Creates a new archive.
• -z: Compresses the archive using gzip.
• -v: Displays verbose output (showing files being added).
• -f: Specifies the archive filename my_archive.tar.gz.

Extracting Archives

To extract the contents of my_archive.tar.gz:

tar -xzvf my_archive.tar.gz

This command uses:

• -x: Extracts the archive.
• -z: Indicates that the archive is compressed with gzip.
• -v: Provides verbose output.
• -f: Specifies the archive filename.

Listing Archive Contents

To list the files within my_archive.tar.gz without extracting:

tar -tvf my_archive.tar.gz

This command uses:

• -t: Lists the archive contents.
• -v: Shows verbose output.
• -f: Specifies the archive filename.

Using Different Compression Algorithms

You can use different compression algorithms by changing the options. For example, to create an archive compressed with bzip2:

tar -cjvf my_archive.tar.bz2 file1.txt file2.txt my_directory

And to use xz compression:

tar -cJvf my_archive.tar.xz file1.txt file2.txt my_directory

Adding Files to an Existing Archive

While tar doesn’t directly support adding files to an existing archive, you can achieve this by extracting the archive, adding the new files, and then creating a new archive. Alternatively, some specialized tools can append to certain archive types, but this is beyond the scope of basic tar usage.

Wildcards and Recursive Operations

tar supports wildcards (*, ?, [...]) for selecting files and the -r option for recursively adding directories. For instance, to archive all .txt files in the current directory and its subdirectories:

tar -czvf my_archive.tar.gz **/*.txt

This utilizes the ** wildcard for recursive directory traversal. Remember that this requires Bash’s extended globbing to be enabled. You can enable this by running shopt -s globstar before using this command.

Handling Specific Files and Directories

To include or exclude specific files or directories during archiving, you can use the --exclude option along with the -I option which includes files matching a specific pattern. For example, to archive everything except file2.txt:

tar -czvf my_archive.tar.gz --exclude=file2.txt *

These examples demonstrate the fundamental usage of tar. Exploring its numerous options and combining them effectively unlocks its full potential for efficient file management in Linux. Remember to consult the man tar page for a complete reference.