What language is used by bosun?

From their quickstart guide I got this following sample

alert cpu.is.too.high {
    template = test
    $metric = q("sum:rate{counter,,1}:os.cpu{host=your-system-here}", "1h", "")
    $avgcpu = avg($metric)
    crit = $avgcpu > 80
    warn = $avgcpu > 60
}

I would guess it's a perlish DSL. What is the name of this language?

We just call it "Bosun's expression language" and is documented at http://bosun.org/expressions.html. As you said it is a custom DSL. It currently has the following qualities

• It is not imperative. The language itself actually lacks true variables, the "$foo" are just text replacement
• It is functional
• It is well typed (functions accept and return specific types. Since the DSL is for alerting, we believe it is important to catch as many errors at possible at parse time.)

The guts implementation of the parser and lexer is based on that guts of text/template. A map function that takes an expression to operator on every X item in a series for an entire seriesSet is in the works, so the language is still a bit in the works. But I don't think we will be change the underlying design choices mentioned above (except maybe actually use real variables instead of text replacement at some point.)