The _uuuu_llll command reads the named _f_i_l_e_n_a_m_es (or the standard input if none
are given) and translates occurrences of underscores to the sequence
which indicates underlining for the terminal in use, as specified by the
environment variable _TTTT_EEEE_RRRR_MMMM. _uuuu_llll uses the appropriate
_////_uuuu_ssss_rrrr_////_ssss_hhhh_aaaa_rrrr_eeee_////_llll_iiii_bbbb_////_tttt_eeee_rrrr_mmmm_iiii_nnnn_ffff_oooo file to determine the character sequences for
underlining. If the terminal is incapable of underlining, but is capable
of a standout mode then that is used instead. If the terminal can
overstrike, or handles underlining automatically, _uuuu_llll degenerates to _cccc_aaaa_tttt.
If the terminal cannot underline, underlining is ignored.
The following options are available:
_----_tttt _t_e_r_m_i_n_a_l Override the terminal kind specified in the environment. If
the terminal cannot underline, underlining is ignored.
_----_iiii Indicate underlining by a separate line containing
appropriate dashes _----; this is useful when you want to look at
the underlining which is present in an _nnnn_rrrr_oooo_ffff_ffff output stream on
a CRT-terminal.
_----_bbbb Use bold if a combination of attributes is present (for
example, underlining plus bold). The default in this
situation is to use reverse video. The manual pages look
better with this option, so _mmmm_aaaa_nnnn(1) uses it by default.