external_encoding

Returns the external encoding for files read from +ARGF+ as an +Encoding+
object. The external encoding is the encoding of the text as stored in a
file. Contrast with +ARGF.internal_encoding+, which is the encoding used
to represent this text within Ruby.

To set the external encoding use +ARGF.set_encoding+.

ARGF.external_encoding  #=>  #<Encoding:UTF-8>