col(C)

col -- filter reverse linefeeds

Syntax

col [ -bfpx ]

Description

col prepares output from processes, such as the nroff text formatter for output on devices that limit or do not allow reverse or half-line motions. col is typically used to process nroff output text that contains tables generated by the tbl program. A typical command line might be:

tbl file | nroff | col | lpr

col takes the following options:

-b: Assumes the output device in use is not capable of backspacing. If two or more characters appear in the same place, col outputs the last character read.
-f: Allows forward half linefeeds. If not given, col accepts half line motions in its input, but text that would appear between lines is moved down to the next full line. Reverse full and half linefeeds are never allowed with this option.
-x: Prevents conversion of whitespace to tabs on output. col normally converts whitespace to tabs wherever possible to shorten printing time.
-p: Causes col to ignore unknown escape sequences found in its input and pass them to the output as regular characters. Because these characters are subject to overprinting from reverse line motions, the use of this option is discouraged unless the user is fully aware of the position of the escape sequences.

col assumes that the ASCII control characters SO (octal 016) and SI (octal 017) start and end text in an alternate character set. If you have a reverse linefeed (ESC 7), reverse half linefeed (ESC 8), or forward half linefeed (ESC 9), within an SI-SO sequence, the ESC 7, 8 and 9 are still recognized as line motions.

On input, the only control characters col accepts are Space, Backspace, Tab, Return, Newline, reverse linefeed (ESC 7), reverse half linefeed (ESC 8), forward half linefeed (ESC 9), alternate character start(SI), alternate character end (SO), and vertical tag (VT). (The VT character is an alternate form of full reverse linefeed, included for compatibility with some earlier programs of this type.) All other non-printing characters are ignored.

Exit values

col returns the following values:

0: successful completion
>0: an error occurred

Limitations

col cannot back up more than 128 lines.

col allows at most 800 characters, including backspaces, on a line.

Vertical motions that would back up over the first line of the document are ignored. Therefore, the first line must not contain any superscripts.

Standards conformance

col is conformant with:

AT&T SVID Issue 2;
X/Open CAE Specification, Commands and Utilities, Issue 4, 1992: note that this command is marked as to be withdrawn.