Protecting Wildcards From Shell With Tar: A Simple Guide

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Protecting wildcards from shell expansion is crucial when working with tar, a popular command-line utility for archiving and compressing files. In this article, we will explore the importance of shielding wildcards and provide a step-by-step guide on how to do it using tar.

Why Protect Wildcards?

When using tar, wildcards are essential for specifying files and directories to be archived or extracted. However, if not properly shielded, these wildcards can be interpreted by the shell, leading to unexpected results or even errors. By protecting wildcards, you ensure that they are passed to tar as intended, rather than being expanded by the shell.

Understanding Shell Expansion

Before we dive into the solution, let's quickly understand how shell expansion works. When you use a wildcard, such as an asterisk (*) or a question mark (?), the shell expands it to match files and directories in the current working directory. For example, the command tar -cf archive.tar * would expand the wildcard to include all files in the current directory, which may not be the intended behavior.

Using Quotes to Shield Wildcards

The simplest way to protect wildcards from shell expansion is to enclose them in quotes. By wrapping the wildcard in single quotes (') or double quotes ("), you prevent the shell from interpreting it. Here's an example:

tar -cf archive.tar '*/path/to/files'

In this example, the wildcard */path/to/files is enclosed in single quotes, ensuring that it is passed to tar as a literal string.

Using Escape Characters

Another way to shield wildcards is to use escape characters. You can prefix the wildcard with a backslash (\) to prevent shell expansion. Here's an example:

tar -cf archive.tar \*/path/to/files

In this example, the backslash before the wildcard prevents the shell from interpreting it.

Using tar's --wildcards Option

tar provides a --wildcards option that allows you to specify wildcards without shielding them from the shell. This option tells tar to treat the wildcard as a literal string, rather than expanding it. Here's an example:

tar --wildcards -cf archive.tar */path/to/files

Best Practices

To avoid issues with shell expansion, follow these best practices when using tar with wildcards:

• Always enclose wildcards in quotes or use escape characters to shield them from the shell.
• Use tar's --wildcards option to specify wildcards without shielding them.
• Be cautious when using wildcards in combination with other options, such as -C or --directory.

Common Use Cases

Shielding wildcards is essential in various scenarios, including:

• Archiving files and directories with specific names or patterns.
• Extracting files and directories from an archive using wildcards.
• Creating tarballs with specific files or directories.

Gallery of tar Wildcards

Frequently Asked Questions

By following the best practices outlined in this article, you can ensure that your wildcards are properly shielded from shell expansion when using tar. Remember to enclose wildcards in quotes or use escape characters, and consider using tar's --wildcards option for added convenience.