FOLD(1P) - phpMan

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  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 char-
       acter 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 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>.
       <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 speci-
       fied. 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  Vari-
              ables  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>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 charac-
       ter  (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> backs up one column position and  out-
       puts  enough  <backspace>s to return to the start of the character when
       <backspace> is used to provide local line motions to support  underlin-
       ing  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 charac-
       ter 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 histori-
       cal 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 Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  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 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 .

IEEE/The Open Group                  2003                             FOLD(1P)