> _,$ are sometimes injected as a general-utility global variable in languages with deficient standard libraries I would say that underscore is used as convent

> _,$ are sometimes injected as a general-utility global variable in languages with deficient standard libraries I would say that underscore is used as convention. There are languages where the underscore is either tool supported or language reserved for this purpose broadly or in limited context (lambdas). Languages that use underscore for ignored values include Java, Erlang, Python, Scala, Clojure, F#, SML, Swift, et al.