MAGICIEL

MAGICIEL is an Emacs Lisp implementation of the file and magic file content and type guessing machinery available on UN*X systems.

There are two reasons for its existence.

1. Installing the C dll on Windows is a P.I.T.A. for my standards.
2. An Emacs Lisp (and, next, a Common Lisp) version is useful per se.
3. Why not doing it? It is just one of the many rabbit holes I fall into.
4. You do not want to know which rabbit hole led to this one.
5. Did I say there were two reasons?

Goals

The final version (available "very soon now" (tm)) will allow you to get information about a file (and MIME information) directly from Emacs Lisp.

Also, the library will allow you to load and compile magic(5) files in a modular way.

Installing and Using MAGICIEL

To use the package, just install the folder magiciel in your Emacs setup and ensure that the file magiciel.el is loaded. Eventually, it will get into melpa.

Using MAGICIEL

The main command (and function) to use is magiciel-divine, described below.

(magiciel-divine FILENAME &optional (CONTEXT :normal)) 

The type of FILENAME will be divined by the call.

CONTEXT can be either :normal or !:normal, in which case the function will return a description of the file content (as per the simple use of the UN*X file command; or CONTEXT can be !:mime in which case it will return the MIME type of the file (or "application/octet-stream" or "data" as last resort). Finally, CONTEXT can be !:ext, in which case the function will return the most likely extension for FILENAME, by querying the magic spells (i.e., not by looking at the filename extension).

If called interactively, the command will default to :normal CONTEXT, unless invoked with a prefix (use the ?d choice for :normal operation in that case).

Nice to have...

• Eventually, it'd be nice to have a sexpy magic format.
• Integration with dired et similia, is also a desirable goal.

An Overview of the "Compilation" Flow

The flow is essentially the following.

1. A magic(5) file is read line by line.
2. A line is parsed in a magiciel--magic-record by the function magiciel--parse-magic-record (in file parse-magic.el).
3. A magiciel--magic-record is "compiled" in a magiciel--instruction by the function magiciel--compile-record, which is actually called by magiciel-compile-magic; the last function does also other things like organizing the test tree implied in the magic(5) specifications (in file compile-magic.el).
4. The function magiciel--compile-record is just a wrapper around magiciel--compile-instr which generates magiciel--instructions.
5. The magiciel-instructions generated are then emitted by magiciel--emit (always in file compile-magic.el), which is called by magiciel--group-emit from magiciel--magic-emit.

A NOTE ON FORKING

Of course you are free to fork the project subject to the current licensing scheme. However, before you do so, I ask you to consider plain old "cooperation" by asking me to become a developer. It helps keeping the entropy level at an acceptable level.

Enjoy

Marco Antoniotti, Milan, Italy, (c) 2024