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- reverse line-feeds filter
The col utility reads from the standard input and writes to the standard output. It performs the line overlays implied by reverse line-feeds, and by forward and reverse half-line-feeds. Unless -x is used, all blank characters in the input will be converted to tab characters wherever possible. col is particularly useful for filtering multi-column output made with the .rt command of nroff(1) and output resulting from use of the tbl(1) preprocessor.
The ASCII control characters SO and SI are assumed by col to start and end text in an alternative character set. The character set to which each input character belongs is remembered, and on output SI and SO characters are generated as appropriate to ensure that each character is written in the correct character set.
On input, the only control characters accepted are space, backspace, tab, carriage-return and newline characters, SI, SO, VT, reverse line-feed, forward half-line-feed and reverse half-line-feed. The VT character is an alternative form of full reverse line-feed, included for compatibility with some earlier programs of this type. The only other characters to be copied to the output are those that are printable.
The ASCII codes for the control functions and line-motion sequences mentioned above are as given in the table below. ESC stands for the ASCII escape character, with the octal code 033; ESC- means a sequence of two characters, ESC followed by the character x.
Assume that the output device in use is not capable of backspacing. In this case, if two or more characters are to appear in the same place, only the last one read will be output.
Although col accepts half-line motions in its input, it normally does not emit them on output. Instead, text that would appear between lines is moved to the next lower full-line boundary. This treatment can be suppressed by the -f (fine) option; in this case, the output from col may contain forward half-line-feeds (ESC-9), but will still never contain either kind of reverse line motion.
Normally, col will ignore any escape sequences unknown to it that are found in its input; the -p option may be used to cause col to output these sequences as regular characters, subject to overprinting from reverse line motions. The use of this option is highly discouraged unless the user is fully aware of the textual position of the escape sequences.
Prevent col from converting blank characters to tab characters on output wherever possible. Tab stops are considered to be at each column position n such that n modulo 8 equals 1.
See environ(5) for descriptions of the following environment variables that affect the execution of col: LC_CTYPE, LC_MESSAGES, and NLSPATH.
The following error values are returned:
An error occurred.
See attributes(5) for descriptions of the following attributes:
The input format accepted by col matches the output produced by nroff with either the -T37 or -Tlp options. Use -T37 (and the -f option of col) if the ultimate disposition of the output of col will be a device that can interpret half-line motions, and -Tlp otherwise.
col cannot back up more than 128 lines or handle more than 800 characters per line.
Local vertical motions that would result in backing up over the first line of the document are ignored. As a result, the first line must not have any superscripts.