fold(P)                                                 fold(P)





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  pos-
       sible  that does not exceed the specified number of col-
       umn 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>s, <backspace>s, or <tab>s are
       encountered in the input, and the -b option is not spec-
       ified, they shall be treated specially:

       <backspace>
              The  current  count of line width shall be decre-
              mented by one, although  the  count  never  shall
              become  negative.  The  fold  utility  shall  not
              insert a <newline> immediately  before  or  after
              any <backspace>.

       <carriage-return>

              The  current  count of line width shall be set to
              zero. The fold utility shall not insert  a  <new-
              line>  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 IEEE Std 1003.1-2001,  Section  12.2,  Utility
       Syntax Guidelines.

       The following options shall be supported:

       -b     Count  width  in  bytes  rather than column posi-
              tions.

       -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>  meet-
              ing 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  posi-
              tions  (or bytes if -b is specified). The results
              are unspecified if width is not a positive  deci-
              mal 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 only if no file oper-
       ands are specified. 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 internationaliza-
              tion  variables  that are unset or null. (See the
              Base Definitions volume of  IEEE Std 1003.1-2001,
              Section  8.2,  Internationalization Variables for
              the precedence of internationalization  variables
              used  to  determine  the  values  of locale cate-
              gories.)

       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 con-
              stant-width font output device.

       LC_MESSAGES
              Determine the  locale  that  should  be  used  to
              affect the format and contents of diagnostic mes-
              sages 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>s.

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 cor-
       rectly; the interpretation depends entirely on the phys-
       ical 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> backs up one column
       position and outputs enough <backspace>s  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

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in
       electronic form from  IEEE  Std  1003.1,  2003  Edition,
       Standard  for Information Technology -- Portable Operat-
       ing System Interface (POSIX), The Open Group Base Speci-
       fications Issue 6, Copyright (C) 2001-2003 by the Insti-
       tute 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.open-
       group.org/unix/online.html .



POSIX                         2003                      fold(P)
