PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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:

       <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         top

       The fold utility shall conform to the Base Definitions volume of
       POSIX.1‐2008, 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 used.

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.

ENVIRONMENT VARIABLES         top

       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.1‐2008, 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         top

       Default.

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

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

        0    All input files were processed successfully.

       >0    An error occurred.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       cut(1p)

       The Base Definitions volume of POSIX.1‐2008, 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, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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.unix.org/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                 2013                            FOLD(1P)