filter reverse line feeds and backspaces from
filters out reverse (and half-reverse)
line feeds so that the output is in the correct order with only forward and
half-forward line feeds, and replaces whitespace characters with tabs where
reads from the standard input and writes
to the standard output.
The options are as follows:
- Do not output any backspaces, printing only the last character written to
each column position. This can be useful in processing the output of
- Forward half-line feeds are permitted (“fine” mode).
Normally characters printed on a half-line boundary are printed on the
- Compress spaces into tabs. This is the default behavior.
- Buffer at least num lines in memory. By
default, 128 lines are buffered.
- Output multiple spaces instead of tabs.
In the input stream,
understands both the
escape sequences of the form escape-digit mandated by
Version 2 of the Single UNIX Specification
and the traditional BSD
format escape-control-character. The control sequences for carriage motion and
their ASCII values are as follows:
- Reverse line feed (27 then 7).
- Reverse line feed (27 then 55).
- Half reverse line feed (27 then 8).
- Half reverse line feed (27 then 56).
- Half forward line feed (27 then 9).
- Half forward line feed (27 then 57). In
-f mode, this sequence may also occur
in the output stream.
- Moves back one column (8); ignored in the first column.
- carriage return
- Forward line feed (10); also does carriage return.
- shift in
- Shift to normal character set (15).
- shift out
- Shift to alternate character set (14).
- Moves forward one column (32).
- Moves forward to next tab stop (9).
- vertical tab
- Reverse line feed (11).
All unrecognized control characters and escape sequences are discarded.
keeps track of the character set as
characters are read and makes sure the character set is correct when they are
If the input attempts to back up to the last flushed line,
will display a warning message.
command appeared in
Version 6 AT&T UNIX