How to Use the 'shar' Command (with Examples)

The shar command is a tool used to create shell archives, which are shell scripts capable of extracting files packaged within them. Similar to creating a zip or tar file, shar wraps files in a script format that can be easily transferred and executed to unpack the contents. This is particularly useful for distributing files in environments where traditional archive utilities might not be available, as shar archives can be extracted using any shell interpreter.

Use case 1: Create a Shell Script to Extract Files

Code:

shar --vanilla-operation path/to/file1 path/to/file2 ... > path/to/archive.sh

Motivation:

Creating a standalone shell script that can extract its own contents is useful when distributing files to systems that might not have a broad array of utility tools. Users merely need a shell, such as bash or sh, to restore files from the archive, simplifying distribution to various systems.

Explanation:

• shar: The command to create a shell archive.
• --vanilla-operation: Instructs shar to perform its basic, core operation without additional features. The primary goal here is to encapsulate the files into a single executable script.
• path/to/file1 path/to/file2 ...: Specifies the list of files to include in the archive.
• > path/to/archive.sh: Redirects the output, which is the shell archive, to a file named archive.sh.

Example Output:

Executing this command will result in the creation of archive.sh, which when run (sh archive.sh), will extract the specified files into the current directory.

Use case 2: Compress the Files in the Archive

Code:

shar --compactor xz path/to/file1 path/to/file2 ... > path/to/archive.sh

Motivation:

Adding compression to the shell archive reduces the total size, which is beneficial for minimizing bandwidth during transfers or decreasing storage usage. This is particularly advantageous when files are large or numerous.

Explanation:

• shar: The command to create a shell archive.
• --compactor xz: This argument specifies that xz compression should be applied to the included files. xz is known for providing excellent compression ratios.
• path/to/file1 path/to/file2 ...: These are the files that will be included and compressed in the archive.
• > path/to/archive.sh: Redirects the compressed output to a shell script archive.sh.

Example Output:

The output will be a compressed self-extracting script archive.sh that, when executed, will decompress and extract the files in the current directory.

Use case 3: Treat All Files as Binary

Code:

shar --uuencode path/to/file1 path/to/file2 ... > path/to/archive.sh

Motivation:

Treating files as binary ensures that they are encoded in a manner that’s safe for transport across systems that may interpret binary data unpredictably. Uuencoding prevents corruption during email transfers or when saving files in text-based systems.

Explanation:

• shar: The command used to create a shell archive.
• --uuencode: This option encodes all files in uuencode format, which is binary-safe and can be decoded easily within a shell script.
• path/to/file1 path/to/file2 ...: Files to be uuencoded into the archive.
• > path/to/archive.sh: Writes the uuencoded archive script output to archive.sh.

Example Output:

The generated archive.sh will contain uuencoded data that, when executed, will decode and extract the files as originally intended.

Use case 4: Treat All Files as Text

Code:

shar --text-files path/to/file1 path/to/file2 ... > path/to/archive.sh

Motivation:

If you know that all included files are plaintext, you might prefer to avoid unnecessary encoding overhead. Treating everything as text can simplify extraction and reduce file size slightly if binary encoding methods cause bloat.

Explanation:

• shar: The command to create a shell archive.
• --text-files: Instructs shar that all files should be treated as plaintext, avoiding unnecessary binary encoding.
• path/to/file1 path/to/file2 ...: Files to be archived, treated entirely as text.
• > path/to/archive.sh: Output file for the shell script archive.

Example Output:

archive.sh will be created with the plaintext data included and ready for extraction.

Use case 5: Include Name and Cut Mark in Header

Code:

shar --archive-name "My files" --cut-mark path/to/file1 path/to/file2 ... > path/to/archive.sh

Motivation:

Including a descriptive name and a cut mark in the archive’s header provides context and structure. The cut mark delineates the beginning of the archived content, while the name provides identifiable information about the data set.

Explanation:

• shar: Command to create a shell archive.
• --archive-name "My files": Specifies a label or name for the archive, which is included in the script header.
• --cut-mark: Includes a cut mark in the script, making it clearer where the extracted content starts.
• path/to/file1 path/to/file2 ...: Files to be included in the archive.
• > path/to/archive.sh: Redirects the specially labeled archive to archive.sh.

Example Output:

The resulting script will start with a header specifying “My files” and includes a cut mark, providing clarity about its contents and structure when viewed or edited.

Conclusion:

Overall, the shar command presents multifaceted solutions for packaging and distributing files as shell scripts, making it highly versatile for system administrators and developers seeking universal and simplified extraction processes across various environments. Each use case above addresses specific needs, from file compression and binary safety to ease of distribution and organization. With these examples, leveraging the full potential of shar can streamline file management in diverse scenarios.