Unlike Windows systems which uses extensions to distinguish between files, in Unix philosophy filetype is what used to recognize a file.

In other words, systems like BSD or Linux doesn’t depend on the extension to know the type of a file whether it’s mp3 or jpg or png, etc. This is done by a command called file, and file uses magic(5) internally.

In Ruby however, there are gems like ruby-filemagic which is dead. There are still forked copy. But we have created another alive gem called libmagic_rb. It uses magic(5) for detecting the mimetype of a file. The differences between gem and other gems are:

• It can work with older version of libmagic: libmagic_rb is written for older systems as well as newer system. It supports decade old systems like CentOS or AmazonLinux. It also supports Ruby 1.9+.
• You can pass various options to libmagic_rb: LibmagicRb (class) can accept various options that are supported by magic(5) during compilation.
• It’s very fast: libmagic_rb is written in Pure C. Apart from C to Ruby datatype convertion, it just does what you are told to do. So checking millions of files isn’t a time consuming thing.

Here’s how it works!

Let’s say you have a file called hello.jpg, here what it can do:

require 'libmagic_rb'

LibmagicRb.check(file: 'hello.jpg')  # => "image/jpeg; charset=binary"

LibmagicRb.check(
  file: 'hello.jpg',
  mode: LibmagicRb::MAGIC_RAW
)  # => "JPEG image data, JFIF standard 1.01, aspect ratio, density 1x1, segment length 16, progressive, precision 8, 3072x2036, components 3"

It’s as easy as that. Using the magic library, it also lets you dig through the EXIF data of the file.

The installation and other details can be found on the GitHub page for libmagic_rb. As usual, the gem can be found on Rubygems.org.

Please Let us know your thoughts below!