The fold utility is a filter that will fold lines from its input files, breaking the lines to have a maximum of width column positions (or bytes, if the -b option is specified). Lines will be broken by the insertion of a NEWLINE character such that each output line (referred to later in this section as a segment) is the maximum width possible that does not exceed the specified number of column positions (or bytes). A line will not be broken in the middle of a character. The behavior is undefined if width is less than the number of columns any single character in the input would occupy.

If the CARRIAGE-RETURN, BACKSPACE, or TAB characters are encountered in the input, and the -b option is not specified, they will be treated specially:

BACKSPACE

The current count of line width will be decremented by one, although the count never will become negative. fold will not insert a NEWLINE character immediately before or after any BACKSPACE character.

CARRIAGE-RETURN

The current count of line width will be set to 0. fold will not insert a NEWLINE character immediately before or after any CARRIAGE-RETURN character.

TAB

Each TAB character encountered will advance the column position pointer to the next tab stop. Tab stops will be at each column position n such that n modulo 8 equals 1.

The following options are supported:

-b

Count width in bytes rather than column positions.

-s

If a segment of a line contains a blank character within the first width column positions (or bytes), break the line after the last such blank character meeting the width constraints. If there is no blank character meeting the requirements, the -s option will have no effect for that output segment of the input line.

-w width|-width

Specify the maximum line length, in column positions (or bytes if -b is specified). If width is not a positive decimal number, an error is returned. The default value is 80.

The following operand is supported:

file

A path name of a text file to be folded. If no file operands are specified, the standard input will be used.

See environ(5) for descriptions of the following environment variables that affect the execution of fold: LC_CTYPE, LC_MESSAGES, and NLSPATH.

The following exit values are returned:

0

All input files were processed successfully.

>0

An error occurred.

See attributes(5) for descriptions of the following attributes:

cut(1), pr(1), attributes(5), environ(5)

fold and cut(1) can be used to create text files out of files with arbitrary line lengths. fold should be used when the contents of long lines need to be kept contiguous. cut should be used when the number of lines (or records) needs to remain constant.

fold is frequently used to send text files to line printers that truncate, rather than fold, lines wider than the printer is able to print (usually 80 or 132 column positions).

fold may not work correctly if underlining is present.