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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 dif-
       fer (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>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 decremented by one, although the count never shall become nega-
              tive. 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  <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 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 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 only if no file operands 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 internationalization variables that are unset or  null.  (See  the  Base
              Definitions  volume  of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the prece-
              dence 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 exam-
              ple, single-byte as opposed to multi-byte characters in arguments and input files), and for the determi-
              nation  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  writ-
              ten 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 correctly; 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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (C) 2001-2003 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 Stan-
       dard,  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 .



IEEE/The Open Group                  2003                             FOLD(1P)