COLCRT(1)                    General Commands Manual                   COLCRT(1)

     colcrt – filter nroff output for CRT previewing

     colcrt [-] [-2] [file ...]

     The colcrt utility provides virtual half-line and reverse line feed
     sequences for terminals without such capability, and on which overstriking
     is destructive.  Half-line characters and underlining (changed to dashing
     `-') are placed on new lines in between the normal output lines.

     The following options are available:

     -       Suppress all underlining.  This option is especially useful for
             previewing allboxed tables from tbl(1).

     -2      Cause all half-lines to be printed, effectively double spacing the
             output.  Normally, a minimal space output format is used which will
             suppress empty lines.  The program never suppresses two consecutive
             empty lines, however.  The -2 option is useful for sending output
             to the line printer when the output contains superscripts and
             subscripts which would otherwise be invisible.

     The LANG, LC_ALL and LC_CTYPE environment variables affect the execution of
     colcrt as described in environ(7).

     A typical use of colcrt would be

     tbl exum2.n | nroff -ms | colcrt - | more

     The colcrt utility exits 0 on success, and >0 if an error occurs.

     col(1), more(1), nroff(1), troff(1), ul(1)

     Should fold underlines onto blanks even with the ‘-’ option so that a true
     underline character would show.

     Can't back up more than 102 lines.

     General overstriking is lost; as a special case ‘|’ overstruck with ‘-’ or
     underline becomes ‘+’.

     Lines are trimmed to 132 characters.

     Some provision should be made for processing superscripts and subscripts in
     documents which are already double-spaced.

     Characters that take up more than one column position may not be underlined

     The colcrt command appeared in 3.0BSD.

macOS 12.1                        July 31, 2004                       macOS 12.1