reads the named files (or standard input if none are given)
and translates occurances of underscores to the sequence
which indicates underlining.
is used as the terminal kind.
Otherwise, the environment is looked in and
the appropriate sequences for underlining.
are present, standout mode is used to indicate underlining.
If the terminal can overstrike,
or handles underlining automatically,
If the terminal cannot underline, underlining is ignored.
usually outputs a series of backspaces and underlines intermixed
with the text to indicate underlining. No attempt is made to optimize