How to use the command nokogiri (with examples)

Nokogiri is a command-line tool used for parsing HTML, XML, SAX, and Reader data. It provides various options to customize the parsing process and supports features like loading initialization files, specifying encoding, validating using RELAX NG files, and more. In this article, we will explore different use cases of the Nokogiri command with examples.

Use case 1: Parse the contents of a URL or file

Code:

nokogiri http://example.com/page.html

Motivation:

Parsing the contents of a URL or file is one of the basic use cases of the Nokogiri command. This allows you to extract data from websites, process XML documents, and perform various operations on the parsed data.

Explanation:

• nokogiri is the command name.
• http://example.com/page.html is the URL or path to the file containing the data you want to parse.

Example output:

The output will vary based on the contents being parsed. For example, if you are parsing an HTML page, the output could be the extracted text, HTML structure, or specific elements you are interested in.

Use case 2: Parse as a specific type

Code:

nokogiri path/to/file --type xml

Motivation:

Parsing as a specific type allows you to indicate the format of the data being processed. This is useful when dealing with different types of data like XML or HTML, as it helps the parser understand the structure and apply appropriate parsing logic.

Explanation:

• --type is the flag to specify the type of data.
• xml is the specific type you want to parse the data as.

Example output:

The output will be the parsed data represented in the specified type. For example, if you specify --type xml, the output could be the XML structure of the parsed data.

Use case 3: Load a specific initialization file before parsing

Code:

nokogiri path/to/file -C path/to/config_file

Motivation:

Loading a specific initialization file allows you to define custom settings or configurations for the parsing process. This is useful when you have pre-defined rules or requirements that need to be applied during parsing.

Explanation:

• -C is the flag to specify the path to the initialization file.
• path/to/config_file is the path to the configuration file you want to load.

Example output:

The output will be the parsed data with the custom settings or configurations applied. For example, the output could include additional metadata or specific transformations based on the loaded initialization file.

Use case 4: Parse using a specific encoding

Code:

nokogiri url|path/to/file --encoding encoding

Motivation:

Parsing using a specific encoding allows you to handle different character encodings correctly. This is important when dealing with data that contains special characters or non-ASCII characters, as using the correct encoding ensures the data is interpreted correctly.

Explanation:

• --encoding is the flag to specify the character encoding.
• encoding is the specific encoding you want to use for parsing.

Example output:

The output will be the parsed data interpreted using the specified encoding. For example, if you specify --encoding utf-8, the output could be the parsed data with all the special characters properly represented.

Use case 5: Validate using a RELAX NG file

Code:

nokogiri url|path/to/file --rng url|path/to/file

Motivation:

Validating using a RELAX NG file allows you to ensure that the parsed data complies with a specific schema or structure. This is helpful when you want to guarantee the integrity and correctness of the data being processed.

Explanation:

• --rng is the flag to specify the RELAX NG file for validation.
• url|path/to/file is the URL or path to the RELAX NG file you want to use for validation.

Example output:

The output will either indicate that the parsed data is valid according to the RELAX NG schema or provide detailed information about the validation errors if any. For example, if the data fails validation, the output could include the specific violations and their locations in the data.

Conclusion:

The Nokogiri command provides a versatile tool for parsing HTML, XML, SAX, and Reader data. By utilizing various options like specifying the type, encoding, validation, and loading initialization files, you can customize the parsing process to suit your specific requirements. Whether you need to extract data from websites, process XML documents, or perform data validation, Nokogiri is a powerful command-line tool to have in your arsenal.