GNU Midnight Commander (MC) Documentation

Midnight Commander (mc) skins are configuration files that define the visual appearance of the interface, including colors, attributes, and character sets.

Skin Structure

1. [skin] Header: Defines color support.
2. Color and Attribute Sections: Define colors for specific UI elements (e.g., [core], [dialog], [editor]).
3. Character Sections: Define UTF-8 characters for frames and widgets (e.g., [lines], [widget-panel]).
4. [aliases] (Optional): Define reusable color/attribute fragments.

Color and Attribute Syntax

Colors and attributes are defined using the following semicolon-separated format: keyword = foreground_color;background_color;attributes

If a value is omitted, mc uses a fallback mechanism:

1. The specific keyword's fallback.
2. The _default_ value of the current section.
3. The _default_ value of the [core] section.

Example Skin Snippet

[skin]
truecolors = true

[aliases]
myfavfg = green
myfavbg = black
myfavattr = bold+italic

[core]
_default_ = myfavfg;myfavbg;myfavattr
selected = ;black

VFS uses an object-oriented approach where different data types (archives, remote systems, filesystems) are treated as classes. Individual archives or connections are instances of these classes.

Class Hierarchy

• vfs (Base)
  • direntry (Base for archives and remote systems)
    • cpio (Archive)
    • tar (Archive)
    • fish (Remote system)
    • ftpfs (Remote system)
  • extfs (Ext-based archives)
  • localfs (Local filesystem)
    • sfs (SFS archives)

Core Concepts

• Multiplexing: vfs.c acts as a multiplexor. It exports POSIX-like functions with an mc_ prefix (e.g., mc_open()). These functions intercept VFS-specific names and route them to the appropriate VFS class.
• Entries and Inodes: Each VFS object has an associated directory tree. Entries can be associated with nameless inodes, which store metadata like size and timestamps (similar to a POSIX struct stat).

The mc event system is designed to decouple event sources from their handlers. It uses a fast binary tree (GTree) structure to organize events into groups, where each event contains a list of handlers (GPtrArray).

Key Concepts

• Decoupling: Instead of calling specific functions (like a VFS message output function), components trigger an event. This allows handlers to be registered, changed, or overridden (e.g., by plugins) without modifying the source of the event.
• Event Grouping: Events are organized into groups (using GTree) to allow efficient categorization.
• Handler Execution Order: Handlers are executed in a "Last In, First Out" (LIFO) order: the most recently added handler is the first to execute. This enables plugins to override standard handlers by adding themselves last.
• Event Propagation Control: A handler returns TRUE to allow subsequent handlers for that event to execute, or FALSE to immediately stop further processing of that event.