fold(1p) — Linux manual page


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

PROLOG         top

       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         top

       fold — filter for folding lines

SYNOPSIS         top

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

DESCRIPTION         top

       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:

                 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.

                 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         top

       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         top

       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

STDIN         top

       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         top

       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.


       The following environment variables shall affect the execution of

       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

                 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.



STDOUT         top

       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         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top




EXIT STATUS         top

       The following exit values shall be returned:

        0    All input files were processed successfully.

       >0    An error occurred.



       The following sections are informative.


       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         top

       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         top

       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.



SEE ALSO         top


       The Base Definitions volume of POSIX.1‐2017, Chapter 8,
       Environment Variables, Section 12.2, Utility Syntax Guidelines

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group               2017                          FOLD(1P)

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