There is a ruby binding to libmagic
that does what you need. It is available as a gem named ruby-filemagic:
gem install ruby-filemagic
Require libmagic-dev
.
The documentation seems a little thin, but this should get you started:
$ irb
irb(main):001:0> require 'filemagic'
=> true
irb(main):002:0> fm = FileMagic.new
=> #<FileMagic:0x7fd4afb0>
irb(main):003:0> fm.file('foo.zip')
=> "Zip archive data, at least v2.0 to extract"
irb(main):004:0>