troff were two separate programs,
the former for TTY output, the latter for everything else. With GNU
troff, both programs are merged into one executable, sending its
output to a device driver (
grotty for TTY devices,
for PostScript, etc.) which interprets the intermediate output of
gtroff. For UNIX
troff it makes sense to talk
about Nroff mode and Troff mode since the differences are
hardcoded. For GNU
troff, this distinction is not appropriate
gtroff simply takes the information given in the font
files for a particular device without handling requests specially if a
TTY output device is used.
Usually, a macro package can be used with all output devices.
Nevertheless, it is sometimes necessary to make a distinction between
TTY and non-TTY devices:
gtroff provides two built-in conditions
‘n’ and ‘t’ for the
requests to decide whether
gtroff shall behave like
Make the ‘t’ built-in condition true (and the ‘n’ built-in condition false) for
whileconditional requests. This is the default if
groff) is started with the -R switch to avoid loading of the start-up files troffrc and troffrc-end. Without -R,
gtroffstays in troff mode if the output device is not a TTY (e.g. `ps').
See Conditionals and Loops, for more details on built-in conditions.