FOLD(1P)						     POSIX Programmer's Manual							  FOLD(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       fold -- filter for folding lines

SYNOPSIS

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

DESCRIPTION

       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> 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  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:

       <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>, unless the following character has a width greater than
		 1 and would cause the line width to exceed width.

       <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>.

       <tab>	 Each <tab> 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.

OPTIONS

       The fold utility shall conform to the Base Definitions volume of POSIX.1-2008, Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       -b	 Count width in bytes rather than column positions.

       -s	 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.

       -w width  Specify the maximum line length, in column positions (or bytes if -b is specified). The results are unspecified if width is not a
		 positive decimal number. The default value shall be 80.

OPERANDS

       The following operand shall be supported:

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

STDIN

       The standard input shall be used if no file operands are specified, and shall be used if a file	operand  is  '-'  and  the  implementation
       treats the '-' as meaning standard input.  Otherwise, the standard input shall not be used.  See the INPUT FILES section.

INPUT FILES

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

ENVIRONMENT VARIABLES

       The following environment variables shall affect the execution of fold:

       LANG	 Provide a default value for the internationalization variables that are unset or  null.  (See	the  Base  Definitions	volume	of
		 POSIX.1-2008,	Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine
		 the values of locale categories.)

       LC_ALL	 If set to a non-empty string value, override the values of all the other internationalization variables.

       LC_CTYPE  Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed
		 to multi-byte 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.

       LC_MESSAGES
		 Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.

       NLSPATH	 Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

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

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       The following exit values shall be returned:

	0    All input files were processed successfully.

       >0    An error occurred.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       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 need to be  kept
       contiguous.

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

EXAMPLES

       An example invocation that submits a file of possibly long lines to the printer (under the assumption that the user knows the line width of
       the printer to be assigned by lp):

	   fold -w 132 bigfile | lp

RATIONALE

       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 actually displays/prints/stores the output. In all known internationalized
       implementations, the utilities producing output for mixed column-width output assume that a <backspace> character backs up one column posi-
       tion  and  outputs  enough  <backspace>	characters  to return 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.

       Historical  versions  of  the  fold  utility assumed 1 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 standard utilities. Note that although the width for the -b option is in bytes, a
       line is never split in the middle of a character.  (It is unspecified what happens if a width is specified that is too small to hold a sin-
       gle character found in the input followed by a <newline>.)

       The tab stops are hardcoded to be every eighth column to meet historical practice.  No  new  method  of	specifying  other  tab	stops  was
       invented.

FUTURE DIRECTIONS

       None.

SEE ALSO

       cut

       The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013								  FOLD(1P)