col(1) General Commands Manual col(1)
NAME
col - filter reverse line-feeds and backspaces
SYNOPSIS
DESCRIPTION
reads from the standard input and writes onto the standard output. It performs the line overlays implied by reverse line feeds (ASCII code
and by forward and reverse half-line feeds and is particularly useful for filtering multi-column output made with the command, and output
resulting from use of the preprocessor (see nroff(1) and tbl(1)).
If the option is given, assumes 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 is output.
If the option is given, assumes the output device is a line printer (rather than a character printer) and removes backspaces in favor of
multiply overstruck full lines. It generates the minimum number of print operations necessary to generate the required number of over-
strikes. (All but the last print operation on a line are separated by carriage returns (
); the last print operation is terminated by a
newline (
).)
Although 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 (fine) option; in this case, the output from may
contain forward half-line feeds (ESC-9), but will still never contain either kind of reverse line motion.
Unless the option is given, converts white space to tabs on output wherever possible to shorten printing time.
The ASCII control characters SO ( 16) and SI ( 17) are assumed by to start and end text in an alternate 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 printed in the correct character set.
On input, the only control characters accepted are space, backspace, tab, return, new-line, SI, SO, and VT, ( 13), and ESC followed by or
The VT character is an alternate form of full reverse line-feed, included for compatibility with some earlier programs of this type. All
other non-printing characters are ignored.
Normally, ignores any unrecognized escape sequences found in its input; the option can be used to cause to output these sequences as regu-
lar 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.
Notes
The input format accepted by matches the output produced by with either the or options. Use (and the option of if the ultimate disposition
of the output of is a device that can interpret half-line motions, and otherwise.
EXTERNAL INFLUENCES
Environment Variables
provides a default value for the internationalization variables that are unset or null. If is unset or null, the default value of "C" (see
lang(5)) is used. If any of the internationalization variables contains an invalid setting, will behave as if all internationalization
variables are set to "C". See environ(5).
If set to a non-empty string value, overrides the values of all the other internationalization variables.
determines the interpretation of text as single and/or multi-byte characters, the classification of characters as printable, and the char-
acters matched by character class expressions in regular expressions.
determines the locale that should be used to affect the format and contents of diagnostic messages written to standard error and informa-
tive messages written to standard output.
determines the location of message catalogues for the processing of
International Code Set Support
Single- and multi-byte character code sets are supported.
EXAMPLES
is used most often with and A common usage is:
(very similar to the usual man(1) command). This command allows vertical bars and outer boxes to be printed for tables. The file is run
through the preprocessor, and the output is then piped through formatting the output using the macros. The formatted output is then piped
through which sets up the vertical bars and aligns the columns in the file. The file is finally piped through the command, which prints
the output to the screen with underlining and highlighting substituted for italic and bold typefaces. The option deletes excess space from
the output so that multiple blank lines are not printed to the screen.
WARNINGS
This command is likely to be withdrawn from X/Open standards. Applications using this command might not be portable to other vendors' sys-
tems.
BUGS
Cannot back up more than 128 lines. Cannot back up across page boundaries.
There is a maximum limit for the number of characters, including backspaces and overstrikes, on a line. The maximum limit is at least 800
characters.
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.
SEE ALSO
nroff(1), tbl(1), ul(1), man(5).
STANDARDS CONFORMANCE
col(1)