Number sign/Hash in filename of file URI

The number sign (#), also known as the hash character, has a special significance in URLs and URIs. It is used to represent a fragment identifier in a URL, which points to a specific section within a resource, such as an HTML document.

When using the number sign in a filename or path of a file URI, it can lead to confusion and unexpected behavior, as the character has a reserved meaning in the context of URLs and URIs.

For example, consider the following file URI with a number sign in the filename:

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file:///path/to/my#file.txt

In this URI, the part after the number sign (#file.txt) will be interpreted as a fragment identifier rather than part of the filename. As a result, the URI will point to the entire file my instead of my#file.txt.

To avoid issues with using the number sign in filenames or paths of file URIs, you should percent-encode the number sign as %23. The percent-encoding represents special characters using a percent sign followed by two hexadecimal digits corresponding to the ASCII value of the character.

Here's the corrected file URI with the number sign percent-encoded:

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file:///path/to/my%23file.txt

With percent-encoding, the URI will correctly point to the file my#file.txt.

In general, it's a good practice to avoid using special characters, including the number sign, in filenames or paths to ensure proper handling and compatibility across different systems and applications. If you need to represent special characters in file names, it's best to percent-encode them according to the rules of the URL encoding standard.