lfs-book/appendixa/file-desc.xml

<sect2><title>Short descriptions</title>

<para><command>file</command> tries to classify each given file. It does
this by performing several tests: filesystem tests, magic number tests, and
language tests. The first test that succeeds determines the result.</para>

<para><command>libmagic</command> contains routines for magic number
recognition, used by the file program.</para>

</sect2>