Preliminary documentation on yara can be found here: Yara User's Manual
The following is YARA in a nutshell from this document:
YARA is a tool aimed at helping malware researchers to identify and classify malware families. With YARA you can create descriptions of malware families based on textual or binary information contained on samples of those families. These descriptions, a.k.a rules, consist patterns and a boolean expression which determines its logic. Rules can be applied to files or running processes in order to determine if it belongs to the described malware family.
You can either install libyara with your prefered package manager, or you
r2pm -i yara3-lib and
r2pm -i yara3 in order to retrieve
latest source, compile, and install the library.
Yara in radare2
radare2 provides several commands, allowing the user, to add or remove rules, scan a file, and list or use rules tags.
You can list the yara commands with the following r2 command
By default, radare2 ships with some common crypto and packers rules that you
can find in
/usr/local/share/radare2/last/yara/ if you installed it r2 or
radare2/shlr/yara/ in the git repo.
They are loaded as soon as you start using the yara plugin.
So you can issue
yara scan and automatically see if your binary is packed
with a known packer.
Load a rule file on the fly, and then scan the currently opened file:
yara3 add /home/name/rules/malware.rules yara3 scan
Because radare2 has support for both yara versions currently,
depending from the version/plugin you've loaded, you need
to use the proper versioned command.
yara3. For example