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Nano and Less Customization

JLine provides built-in support for customizing the behavior of the nano and less commands through configuration files. This page explains how to customize these commands to suit your needs.

Overview​

Both nano and less commands in JLine can be customized using configuration files similar to the standard nanorc format. These configuration files are named jnanorc and jlessrc respectively.

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Configuration Setup​

To set up the configuration for nano and less commands, you need to create a ConfigurationPath object that specifies where to look for configuration files:

ConfigurationPath configPath = new ConfigurationPath(
    Paths.get("/pub/myApp"),                           // application-wide settings
    Paths.get(System.getProperty("user.home"), ".myApp") // user-specific settings
);

Then, you can use this configuration path when creating the Builtins and SystemRegistry objects:

Supplier<Path> workDir = () -> Paths.get("");
Builtins builtins = new Builtins(workDir, configPath, null);
SystemRegistry systemRegistry = new SystemRegistry(parser, terminal, workDir, configPath);
systemRegistry.setCommandRegistries(builtins);

Configuration Options​

The jnanorc/jlessrc file contains the default settings for nano/less. During startup, the command tries to read the user-specific settings first and then its application-wide settings. Application-wide settings are read only if user-specific settings do not exist.

The configuration file accepts a series of set and unset commands, which can be used to configure nano/less on startup without using command-line options.

In addition, the configuration file might have 'include syntaxfile' commands to read self-contained color syntaxes from a syntax file. The syntax file parameter can have '*' and '?' wildcards in its file name.

If neither application-wide nor user-specific settings are found at command startup, then syntax files are searched from a standard installation location: /usr/share/nano.

Example Configuration​

Here's an example of a jnanorc configuration file:

include /usr/share/nano/*.nanorc
set tabstospaces
set autoindent
set tempfile
set historylog search.log

Note that the history log is saved in the user-specific directory, and the file can be shared between nano and less applications.

Theme System​

JLine version > 3.21.0 includes a Theme System that allows highlight rules to be specified in terms of token type names, mixins, and parser configurations, instead of hard-coded colors in nanorc files.

Optional theme system configuration is set by adding a 'theme theme-system-file' command in jnanorc/jlessrc configuration files.

Syntax Highlighting​

JLine's nanorc SyntaxHighlighter works with standard nanorc syntax files.

JLine supports the following nanorc keywords:

  • syntax: Defines a new syntax highlighting rule set
  • color: Defines a color for a specific pattern
  • icolor: Defines a case-insensitive color for a specific pattern

Other nanorc keywords are quietly ignored.

Rebinding Keys​

Key rebinding is not currently supported in JLine's implementation of nano and less.

Best Practices​

When customizing nano and less in JLine, consider these best practices:

  1. Configuration Organization: Keep your configuration files organized and well-documented.

  2. Syntax Highlighting: Use syntax highlighting to improve readability of code and other structured text.

  3. Theme System: Use the theme system to maintain consistent highlighting across different file types.

  4. User-Specific Settings: Provide sensible defaults in application-wide settings, but allow users to override them with user-specific settings.

  5. Documentation: Document your customizations for other users.

  6. Testing: Test your customizations with different types of files to ensure they work as expected.

  7. Performance: Be mindful of performance, especially when defining complex syntax highlighting rules.

  8. Compatibility: Try to maintain compatibility with standard nanorc syntax where possible.