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



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       fold -- filter for folding lines

SSYYNNOOPPSSIISS
       fold [[-bs]] [[-w _w_i_d_t_h]] [[_f_i_l_e...]]

DDEESSCCRRIIPPTTIIOONN
       The _f_o_l_d utility is a filter that shall fold lines from its input
       files, breaking the lines to have a maximum of _w_i_d_t_h column positions
       (or bytes, if the --bb 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 _s_e_g_m_e_n_t) 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 _w_i_d_t_h 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 --bb 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 _f_o_l_d
                 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
                 _w_i_d_t_h.

       <carriage-return>
                 The current count of line width shall be set to zero. The
                 _f_o_l_d 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.

OOPPTTIIOONNSS
       The _f_o_l_d utility shall conform to the Base Definitions volume of
       POSIX.1-2017, _S_e_c_t_i_o_n _1_2_._2, _U_t_i_l_i_t_y _S_y_n_t_a_x _G_u_i_d_e_l_i_n_e_s.

       The following options shall be supported:

       --bb        Count _w_i_d_t_h in bytes rather than column positions.

       --ss        If a segment of a line contains a <blank> within the first
                 _w_i_d_t_h 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 --ss option shall have
                 no effect for that output segment of the input line.

       --ww _w_i_d_t_h  Specify the maximum line length, in column positions (or
                 bytes if --bb is specified). The results are unspecified if
                 _w_i_d_t_h is not a positive decimal number. The default value
                 shall be 80.

OOPPEERRAANNDDSS
       The following operand shall be supported:

       _f_i_l_e      A pathname of a text file to be folded. If no _f_i_l_e operands
                 are specified, the standard input shall be used.

SSTTDDIINN
       The standard input shall be used if no _f_i_l_e operands are specified, and
       shall be used if a _f_i_l_e operand is ''--'' and the implementation treats
       the ''--'' as meaning standard input.  Otherwise, the standard input shall
       not be used.  See the INPUT FILES section.

IINNPPUUTT FFIILLEESS
       If the --bb 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 --bb option is not specified, the input files shall be text files.

EENNVVIIRROONNMMEENNTT VVAARRIIAABBLLEESS
       The following environment variables shall affect the execution of _f_o_l_d:

       _L_A_N_G      Provide a default value for the internationalization
                 variables that are unset or null. (See the Base Definitions
                 volume of POSIX.1-2017, _S_e_c_t_i_o_n _8_._2, _I_n_t_e_r_n_a_t_i_o_n_a_l_i_z_a_t_i_o_n
                 _V_a_r_i_a_b_l_e_s for the precedence of internationalization
                 variables used to determine the values of locale categories.)

       _L_C___A_L_L    If set to a non-empty string value, override the values of
                 all the other internationalization variables.

       _L_C___C_T_Y_P_E  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.

       _L_C___M_E_S_S_A_G_E_S
                 Determine the locale that should be used to affect the format
                 and contents of diagnostic messages written to standard
                 error.

       _N_L_S_P_A_T_H   Determine the location of message catalogs for the processing
                 of _L_C___M_E_S_S_A_G_E_S.

AASSYYNNCCHHRROONNOOUUSS EEVVEENNTTSS
       Default.

SSTTDDOOUUTT
       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.

SSTTDDEERRRR
       The standard error shall be used only for diagnostic messages.

OOUUTTPPUUTT FFIILLEESS
       None.

EEXXTTEENNDDEEDD DDEESSCCRRIIPPTTIIOONN
       None.

EEXXIITT SSTTAATTUUSS
       The following exit values shall be returned:

        0    All input files were processed successfully.

       >0    An error occurred.

CCOONNSSEEQQUUEENNCCEESS OOFF EERRRROORRSS
       Default.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       The _c_u_t and _f_o_l_d utilities can be used to create text files out of
       files with arbitrary line lengths. The _c_u_t utility should be used when
       the number of lines (or records) needs to remain constant. The _f_o_l_d
       utility should be used when the contents of long lines need to be kept
       contiguous.

       The _f_o_l_d 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).

EEXXAAMMPPLLEESS
       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 _l_p):


           fold -w 132 bigfile | lp

RRAATTIIOONNAALLEE
       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
       _f_o_l_d without the --bb 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 _f_o_l_d 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 _f_o_l_d is believed to
       be folding long lines for output to limited-length output devices, this
       capability was preserved as the default case. The --bb option was added
       so that applications could _f_o_l_d files with arbitrary length lines into
       text files that could then be processed by the standard utilities. Note
       that although the width for the --bb 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.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _c_u_t

       The Base Definitions volume of POSIX.1-2017, _C_h_a_p_t_e_r _8, _E_n_v_i_r_o_n_m_e_n_t
       _V_a_r_i_a_b_l_e_s, _S_e_c_t_i_o_n _1_2_._2, _U_t_i_l_i_t_y _S_y_n_t_a_x _G_u_i_d_e_l_i_n_e_s

CCOOPPYYRRIIGGHHTT
       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 http://www.opengroup.org/unix/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                  2017                              FOLD(1)
