Using the Unix `compress` Command (with examples)

The compress command in Unix is used to compress files, reducing their size to save storage space. It uses the Lempel-Ziv coding algorithm for compression. In this article, we will explore different use cases and examples of the compress command, demonstrating how it can be effectively utilized.

Compress specific files

Use the compress command to compress specific files. Simply provide the paths to the files you want to compress as arguments.

Code:

compress path/to/file1 path/to/file2 ...

Motivation: Compressing specific files can help in conserving storage space by reducing their size.

Explanation: The compress command is followed by the paths to the files you want to compress. Multiple files can be compressed simultaneously by specifying their respective paths.

Example output:

Compressing path/to/file1...done
Compressing path/to/file2...done

Compress specific files, ignore non-existent ones

To compress specific files, but ignore any files that do not exist, use the -f flag.

Code:

compress -f path/to/file1 path/to/file2 ...

Motivation: Ignoring non-existent files when compressing can be helpful when working with a large number of files, as it saves time and prevents errors from being raised.

Explanation: The -f flag tells the compress command to ignore any files that do not exist. This flag is particularly useful when compressing multiple files, some of which may not exist.

Example output:

Compressing path/to/file1...done
Compressing path/to/file2...done

Set maximum compression bits

The compress command allows you to set the maximum compression bits, which control the level of compression applied to the files.

Code:

compress -b bits

Motivation: Adjusting the compression bits allows you to have control over the compression level, balancing the trade-off between reduced file size and compression speed.

Explanation: The -b flag, followed by the number of bits (between 9 and 16), sets the maximum compression bits to be used. Higher values result in greater compression, but require more time and computational resources.

Example output:

Setting maximum compression bits to 12...done

Write to stdout (no files are changed)

If you only want to display the compressed output without modifying the original files, use the -c flag to write to the standard output (stdout).

Code:

compress -c path/to/file

Motivation: Writing to stdout can be useful when you want to preview the compressed data before deciding to save it to a file.

Explanation: The -c flag tells the compress command to write the compressed output to stdout. This allows you to view the compressed data without altering the original file.

Example output:

Compressed output for path/to/file:
...

Decompress files (functions like uncompress)

The compress command can also be used for decompression, functioning similarly to the uncompress command.

Code:

compress -d path/to/file

Motivation: Decompressing files is necessary when you want to restore the original data from the compressed version.

Explanation: The -d flag tells the compress command to decompress the specified file. This reverses the compression process and restores the original file.

Example output:

Decompressing path/to/file...done

Display compression percentage

To see the compression percentage of a file, use the -v flag.

Code:

compress -v path/to/file

Motivation: The compression percentage provides insight into the effectiveness of the compression algorithm and helps assess the reduction in file size.

Explanation: The -v flag tells the compress command to display the compression percentage of the specified file. This percentage is calculated by comparing the original file size with the compressed file size.

Example output:

Compression percentage for path/to/file: 75%

In conclusion, the compress command offers a range of functionalities to compress and decompress files efficiently. By utilizing the different options and flags available, you can effectively manage storage space and handle compressed data.