File Packing and Compression

Introduction

In this lab, we will learn how to pack and compress files and directories using common Linux commands such as tar, gzip, and zip. These tools are essential for managing files and directories on Linux systems, allowing you to efficiently store and transfer data. We'll start with basic operations and gradually move to more complex tasks, explaining each step in detail.

Skills Graph

Creating a Sample Directory Structure

Let's begin by creating a sample directory structure to work with. This will help us understand how file packing and compression work with different types of files and directories.

Open your terminal and enter the following commands:

cd ~/project
mkdir -p test_dir/{subdir1,subdir2}
echo "This is file 1" > test_dir/file1.txt
echo "This is file 2" > test_dir/file2.txt
echo "This is in subdir1" > test_dir/subdir1/subfile1.txt
echo "This is in subdir2" > test_dir/subdir2/subfile2.txt

Let's break down what these commands do:

1. cd ~/project: This changes your current directory to the project folder in your home directory.
2. mkdir -p test_dir/{subdir1,subdir2}: This creates a new directory called test_dir and two subdirectories inside it: subdir1 and subdir2. The -p option allows mkdir to create parent directories as needed.
3. The echo commands create text files with some sample content in different locations within our new directory structure.

Now, let's verify the structure we've created:

tree test_dir

If you don't see this output or get an error saying "command not found", don't worry. The tree command might not be installed on your system. You can use ls -R test_dir instead, which will show a similar (though less graphical) output.

Packaging Files with tar

Now that we have our sample directory structure, let's learn about packaging files using the tar command. tar stands for "tape archive" and was originally used to create archives on tape drives. Today, it's commonly used to bundle multiple files and directories into a single file.

Let's package our test_dir:

cd ~/project
tar -cvf test_archive.tar test_dir

Let's break down this command:

• tar: The command we're using to create the archive.
• -c: This option tells tar to create a new archive.
• -v: This stands for "verbose". It makes tar print out the names of the files it's adding to the archive. This is optional but helpful to see what's happening.
• -f: This option is followed by the name of the archive file we want to create.
• test_archive.tar: This is the name we're giving to our new archive file. The .tar extension is conventional for tar archives.
• test_dir: This is the directory we're packaging into the archive.

After running this command, you should see a list of files being added to the archive.

To view the contents of the archive without extracting it, you can use:

tar -tvf test_archive.tar

This command lists (-t) the contents of the archive, verbosely (-v), from the file (-f) named test_archive.tar.

Compressing Files with gzip

Now that we have created a tar archive, let's compress it using gzip:

gzip test_archive.tar

This command will compress test_archive.tar and rename it to test_archive.tar.gz. The original test_archive.tar file will be replaced by the compressed version.

To see the size of the compressed file, you can use the following command:

ls -lh test_archive.tar.gz

The -lh options will show the file size in a human-readable format (like KB, MB, etc.).

It's worth noting that while the .tar.gz extension is common, you might also see .tgz, which is equivalent.

Understanding the Difference Between Packaging and Compression

Now that we've performed both packaging and compression, let's understand the difference between these operations and compare the file sizes.

1. Packaging (Archiving):

   • Purpose: To combine multiple files and directories into a single file.
   • What it does: Groups files together, adding some metadata.
   • Example tool: tar (Tape Archive)
   • Result: The total size of the archive is often slightly larger than the sum of the sizes of all files within it.

2. Compression:

   • Purpose: To reduce the size of a file or an archive.
   • What it does: Applies algorithms to remove redundancy in data, making the file smaller.
   • Example tools: gzip, bzip2, xz
   • Result: The compressed file is smaller than the original, but requires decompression before use.

Let's compare the sizes of our original directory, the tar archive, and the compressed tar.gz file:

## Size of the original directory
echo "Size of the original directory:"
du -sh test_dir

## Size of the tar archive (we'll use the backup we created in Step 2)
echo "Size of the tar archive:"
ls -lh test_archive.tar

## Size of the compressed tar.gz file
echo "Size of the compressed tar.gz file:"
ls -lh test_archive.tar.gz

You'll notice that:

1. The tar archive is slightly larger than the original directory. This is because tar adds some metadata to the archive, such as file names, permissions, and directory structures.
2. The compressed tar.gz file is significantly smaller than both the original directory and the tar archive.

The increase in size after packaging is normal and expected. The tar format adds a small amount of overhead to store file metadata, which is necessary for correctly reconstructing the directory structure when unpacking. This overhead is usually negligible for larger directories but can be noticeable for very small files or directories.

Compression, on the other hand, significantly reduces the file size by identifying and eliminating redundancies in the data. This is particularly effective for text files or files with repetitive content.

Creating a Compressed Archive in One Step

While it's helpful to understand the separate steps of creating a tar archive and then compressing it, in practice, these steps are often combined. The tar command has a built-in option to compress the archive using gzip as it's being created.

Let's create a compressed tar archive of our test_dir in one step:

cd ~/project
tar -czvf test_combined.tar.gz test_dir

This command is similar to what we used before, with one important addition:

• -z: This option tells tar to compress the archive using gzip.

The resulting test_combined.tar.gz file is equivalent to what we created in the previous two steps, but we've done it all at once.

To view the contents of this compressed archive without extracting it:

tar -tzvf test_combined.tar.gz

The -z option here tells tar that we're dealing with a gzip-compressed file.

Extracting Files from a Compressed Archive

Now that we've created compressed archives, it's important to know how to extract files from them. Let's extract the contents of our test_combined.tar.gz file:

mkdir extracted
tar -xzvf test_combined.tar.gz -C extracted

Let's break down this command:

• mkdir extracted: This creates a new directory called extracted where we'll put the contents of our archive.
• tar: The command we're using to extract the archive.
• -x: This option tells tar to extract files from an archive.
• -z: This option is needed because we're dealing with a gzip-compressed file.
• -v: This makes the operation verbose, showing us each file as it's extracted.
• -f: This is followed by the name of the archive file we want to extract from.
• -C extracted: This option tells tar to change to the extracted directory before extracting files.

After running this command, you should see a list of files being extracted.

To verify the extraction, you can use:

tree extracted

Or if tree is not available:

ls -R extracted

This will show you the directory structure and files that were in the archive.

Using zip for Cross-Platform Compatibility

While tar and gzip are common in Linux and Unix-like systems, the zip format is often used for better compatibility with Windows systems. Let's create a zip archive of our test_dir:

cd ~/project
zip -r test_archive.zip test_dir

Here's what this command does:

• zip: The command to create a zip archive.
• -r: This option tells zip to work recursively, including all files and subdirectories.
• test_archive.zip: This is the name we're giving to our zip file.
• test_dir: This is the directory we're adding to the zip archive.

To unzip this archive, you can use:

unzip -d unzipped_files test_archive.zip

The -d option specifies the directory to unzip into. If unzipped_files doesn't exist, unzip will create it.

Zip files have the advantage of being easily recognizable and usable on virtually all operating systems, making them a good choice for sharing files with users on different platforms.

Summary

In this lab, we've learned several important file packing and compression techniques commonly used in Linux:

1. We created a sample directory structure to work with, demonstrating how to organize files and directories.
2. We used tar to package files without compression, which is useful for bundling multiple files and directories together.
3. We learned the difference between packaging and compression, understanding their distinct purposes and use cases.
4. We used gzip to compress files, which can significantly reduce file sizes for storage or transfer.
5. We learned how to combine tar and gzip to create compressed archives in one step, a common operation in Linux systems.
6. We practiced extracting files from compressed archives, an essential skill when working with packaged files.
7. Finally, we used zip for creating archives with better cross-platform compatibility, particularly useful when sharing files with Windows users.

These skills are essential for efficient file management in Linux, especially when dealing with large amounts of data or when transferring files between systems. Remember, compression can significantly reduce file sizes, making storage and transfer much more efficient.

As you continue working with Linux, you'll find these commands invaluable for managing your files and directories. Practice these operations