How to Use the Command 'pax' (with examples)

The pax utility is a versatile tool used for archiving and copying files. Derived from UNIX standards, pax bridges the functionality of tools like cpio and tar, providing a unified interface for file manipulation between archiving, extraction, and copying. It’s particularly useful in environments where managing complex file structures and preserving metadata are critical.

Use case 1: List the Contents of an Archive

Code:

pax -f archive.tar

Motivation:

Listing the contents of an archive is essential when you need to verify the files included without extracting them. This is particularly useful for large archives where unnecessary extraction might be time-consuming. Knowing the exact contents helps in confirming that you have the right files for operations like extraction or copying, and aids in managing storage efficiently.

Explanation:

• pax: The command itself, which stands for Portable Archive Exchange. It is the command-line utility you’re invoking.
• -f: This flag indicates that what follows is the name of the archive file you wish to work with.
• archive.tar: Your target archive whose contents you wish to list. The .tar suffix indicates that the archive is formatted as a tarball.

Example Output:

file1.txt file2.txt directory/
directory/file3.txt

This output shows a simple list, indicating each file or directory that the archive archive.tar contains.

Use case 2: List the Contents of a gzip Archive

Code:

pax -zf archive.tar.gz

Motivation:

Compressed archives are popular because they save disk space and reduce transfer times. If you want to view the contents of a .tar.gz archive (a compressed tarball) without decompressing it fully, pax allows you to do this efficiently. This enables you to ensure that the compressed file includes all necessary components or simply identify specific files to extract.

Explanation:

• pax: Initiates the utility.
• -z: Tells pax to filter the archive through gzip, thus indicating that the archive is compressed and needs to be decompressed before listing the contents.
• -f archive.tar.gz: Specifies the name of the file you are inspecting. It’s understood that this file has been compressed with gzip, as denoted by the .gz extension.

Example Output:

compressed-file1.txt compressed-file2.txt another-directory/
another-directory/compressed-file3.txt

This output lists the files within the compressed archive, much like listing an uncompressed tar file.

Use case 3: Create an Archive from Files

Code:

pax -wf target.tar path/to/file1 path/to/file2 ...

Motivation:

Creating an archive is a fundamental operation when you need to bundle multiple files or directories into a single file. This is essential for distribution, backup, or transfer of data. Using pax for this operation can be beneficial due to its simplicity and efficiency, allowing multiple files to be managed as one entity without cluttering the file system.

Explanation:

• pax: The utility being executed.
• -w: This flag is used for writing files to an archive.
• -f target.tar: Specifies the name of the archive that will be created.
• path/to/file1 path/to/file2 ...: Denotes the files or directories you want to include in your new archive.

Example Output:

As this use case results in the creation of a file, there is no output directly to the terminal. The result is the creation of target.tar containing the specified files.

Use case 4: Create an Archive from Files, Using Output Redirection

Code:

pax -w path/to/file1 path/to/file2 ... > target.tar

Motivation:

Using output redirection to create an archive is particularly useful for redirecting standard output to a file, which can be a more flexible approach in scripting environments. It allows you to leverage Unix pipelines or modify the output behavior programmatically without specifying the -f option.

Explanation:

• pax: The command being run.
• -w: Instructs pax to write to an archive.
• path/to/file1 path/to/file2 ...: The paths of the files you desire to archive.
• >: The shell’s standard redirection operator that directs the output of pax to be written into the specified file, here target.tar.

Example Output:

Similar to Use Case 3, there will be no terminal output. Instead, target.tar is the resultant file.

Use case 5: Extract an Archive into the Current Directory

Code:

pax -rf source.tar

Motivation:

Extracting archives is a common task required to restore backed-up data, install software packages, or inspect archived data. By unpacking the contents of source.tar into the current working directory, you can quickly access and manipulate the files as needed. This operation is crucial for data recovery and verification processes.

Explanation:

• pax: The command line utility employed.
• -r: This flag instructs pax to read files from the archive for extraction.
• -f source.tar: Specifies the archive to extract from, with source.tar being the target archive.

Example Output:

Upon successful execution, the files contained in source.tar will appear in your current directory. There may not be any terminal output unless errors occur.

Use case 6: Copy to a Directory, While Keeping the Original Metadata

Code:

pax -rw path/to/file1 path/to/directory1 path/to/directory2 ... target/

Motivation:

Copying files or directories while preserving metadata is crucial when you need to ensure that ownerships, permissions, and timestamps remain intact. This is particularly important for system backups, data migrations, or when manipulating files that depend on specific file metadata.

Explanation:

• pax: The utility being executed.
• -r: Directs pax to read files.
• -w: Indicates writing to specified locations is intended.
• path/to/file1 path/to/directory1 path/to/directory2 ...: Defines the source files or directories for copying.
• target/: The destination directory where files will be copied, which must already exist. Metadata is preserved during this operation.

Example Output:

This operation does not produce terminal output, but you will find the specified files and directories accurately copied to the target/ directory with their original metadata.

Conclusion:

The pax command-line tool offers robust functionality that covers essential file management tasks such as archiving, compressing, listing, extracting, and copying files while preserving metadata. Its versatile usage makes it an invaluable asset in UNIX-based environments, enabling efficient management of complex file systems with a user-friendly syntax. Each of the provided use cases demonstrates how pax can be applied to streamline operations, providing precise control over file manipulation tasks.