PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding 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.1‐2017,  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.1‐2017, 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 position 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 single 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.1‐2017, 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 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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 Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/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                                   2017                                          FOLD(1POSIX)