FOLD(1) General Commands Manual FOLD(1)

fold — fold lines

fold [-bs] [-w width] [file ...]

The fold utility is a filter that shall 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 shall be broken by the insertion of a <newline> character such that each output line (referred to later in this clause as a segment) is the maximum width possible that does not exceed the specified number of column positions (or bytes). A line shall 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 shall be treated specially: <carriage-return> The current count of line width shall be set to zero. The fold utility shall not insert a <newline> immediately before or after any <carriage-return>.

<backspace> The current count of line width shall be decremented by one, although the count never shall become negative. The fold utility shall not

insert a <newline> immediately before or after any <backspace>. <tab> Each <tab> character encountered shall advance the column position pointer to the next tab stop. Tab stops shall be at each column position n such that n modulo 8 equals 1.

The fold utility shall conform to the utility argument syntax guidelines described in 2.10.2. The following options shall be supported by the implementation:

Count width in bytes rather than column positions.

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

width

Specify the maximum line length, in column positions (or bytes if

is specified). The results are unspecified if width is not a positive decimal number. The default value shall be 80.

The following operand shall be supported by the implementation:

file

A pathname of a text file to be folded. If no file operands are specified, the standard input shall be used.

The standard input shall be used only if no file operands are specified. See Input Files.

If the −b option is specified, the input files shall be text files except that the lines are not limited to bytes in length. If the −b option is not specified, the input files shall be text files.

The following environment variables shall affect the execution of fold:

This variable shall determine the locale to use for the locale categories when both LC_ALL and the corresponding environment variable (beginning with LC_ ) do not specify a locale. See 2.6.

This variable shall determine the locale to be used to override any values for locale categories specified by the settings of LANG or any environment variables beginning with LC_.

This variable shall determine the locale for the interpretation of sequences of bytes of text data as characters (e.g., single- versus multibyte characters in arguments and input files) and for the determination of the width in column positions each character would occupy on a constant-width-font output device.

This variable shall determine the language in which messages should be written.

Default.

The standard output shall be a file containing a sequence of characters whose order shall be preserved from the input file(s), possibly with inserted <newline> characters.

Used only for diagnostic messages.

None.

None.

The fold utility shall exit with one of the following values:

All input files were processed successfully.

An error occurred.

Default.

The cut and fold utilities can be used to create text files out of files with arbitrary line lengths. The cut utility should be used when the number of lines (or records) needs to remain constant. The fold utility should be used when the contents of long lines needs to be kept contiguous. The fold utility 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.) Although terminal input in canonical processing mode requires the erase character (frequently set to <backspace>) to erase the previous character (not byte or column position), terminal output is not buffered and is extremely difficult, if not impossible, to parse correctly; the interpretation depends entirely on the physical device that will actually display/print/store the output. In all known internationalized implementations, the utilities producing output for mixed column width output assume that a <backspace> backs up one column position and outputs enough <backspace>s to get back to the start of the character when <backspace> is used to provide local line motions to support underlining and emboldening operations. Since fold without the −b option is dealing with these same constraints, <backspace> is always treated as backing up one column position rather than backing up one character. An example invocation that submits a file of possibly long lines to the line printer (under the assumption that the user knows the line width of the printer to be assigned by lp): fold -w 132 bigfile | lp

Historical versions of the fold utility assumed one byte was one character and occupied one column position when written out. This is no longer always true. Since the most common usage of fold is believed to be folding long lines for output to limited-length output devices, this capability was preserved as the default case. The −b option was added so that applications could fold files with arbitrary length lines into text files that could then be processed by the utilities in this standard. Note that although the width for the −b option is in bytes, a line will never be split in the middle of a character. (It is unspecified what happens if a width is specified that is too small to hold a single character found in the input followed by a <newline>.) The use of a hyphen as an option to specify standard input was removed from an earlier draft because it adds no functionality and is not historical practice. The tab stops are hardcoded to be every eighth column to meet historical practice. No new method of specifying other tab stops was invented.

September 1991 posix.fail