1FOLD(1P) POSIX Programmer's Manual FOLD(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 fold — filter for folding lines
14
16 fold [−bs] [−w width] [file...]
17
19 The fold utility is a filter that shall fold lines from its input
20 files, breaking the lines to have a maximum of width column positions
21 (or bytes, if the −b option is specified). Lines shall be broken by the
22 insertion of a <newline> such that each output line (referred to later
23 in this section as a segment) is the maximum width possible that does
24 not exceed the specified number of column positions (or bytes). A line
25 shall not be broken in the middle of a character. The behavior is unde‐
26 fined if width is less than the number of columns any single character
27 in the input would occupy.
28 If the <carriage-return>, <backspace>, or <tab> characters are encoun‐
30 tered in the input, and the −b option is not specified, they shall be
31 treated specially:
32 <backspace>
34 The current count of line width shall be decremented by one,
35 although the count never shall become negative. The fold
36 utility shall not insert a <newline> immediately before or
37 after any <backspace>, unless the following character has a
38 width greater than 1 and would cause the line width to exceed
39 width.
40 <carriage-return>
42 The current count of line width shall be set to zero. The
43 fold utility shall not insert a <newline> immediately before
44 or after any <carriage-return>.
45 <tab> Each <tab> encountered shall advance the column position
47 pointer to the next tab stop. Tab stops shall be at each col‐
48 umn position n such that n modulo 8 equals 1.
49
51 The fold utility shall conform to the Base Definitions volume of
52 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
53 The following options shall be supported:
55 −b Count width in bytes rather than column positions.
57 −s If a segment of a line contains a <blank> within the first
59 width column positions (or bytes), break the line after the
60 last such <blank> meeting the width constraints. If there is
61 no <blank> meeting the requirements, the −s option shall have
62 no effect for that output segment of the input line.
63 −w width Specify the maximum line length, in column positions (or
65 bytes if −b is specified). The results are unspecified if
66 width is not a positive decimal number. The default value
67 shall be 80.
68
70 The following operand shall be supported:
71 file A pathname of a text file to be folded. If no file operands
73 are specified, the standard input shall be used.
74
76 The standard input shall be used if no file operands are specified, and
77 shall be used if a file operand is '−' and the implementation treats
78 the '−' as meaning standard input. Otherwise, the standard input shall
79 not be used. See the INPUT FILES section.
80
82 If the −b option is specified, the input files shall be text files
83 except that the lines are not limited to {LINE_MAX} bytes in length. If
84 the −b option is not specified, the input files shall be text files.
85
87 The following environment variables shall affect the execution of fold:
88 LANG Provide a default value for the internationalization vari‐
90 ables that are unset or null. (See the Base Definitions vol‐
91 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
92 ables for the precedence of internationalization variables
93 used to determine the values of locale categories.)
94 LC_ALL If set to a non-empty string value, override the values of
96 all the other internationalization variables.
97 LC_CTYPE Determine the locale for the interpretation of sequences of
99 bytes of text data as characters (for example, single-byte as
100 opposed to multi-byte characters in arguments and input
101 files), and for the determination of the width in column
102 positions each character would occupy on a constant-width
103 font output device.
104 LC_MESSAGES
106 Determine the locale that should be used to affect the format
107 and contents of diagnostic messages written to standard
108 error.
109 NLSPATH Determine the location of message catalogs for the processing
111 of LC_MESSAGES.
112
114 Default.
115
117 The standard output shall be a file containing a sequence of characters
118 whose order shall be preserved from the input files, possibly with
119 inserted <newline> characters.
120
122 The standard error shall be used only for diagnostic messages.
123
125 None.
126
128 None.
129
131 The following exit values shall be returned:
132 0 All input files were processed successfully.
134 >0 An error occurred.
136
138 Default.
139 The following sections are informative.
141
143 The cut and fold utilities can be used to create text files out of
144 files with arbitrary line lengths. The cut utility should be used when
145 the number of lines (or records) needs to remain constant. The fold
146 utility should be used when the contents of long lines need to be kept
147 contiguous.
148 The fold utility is frequently used to send text files to printers that
150 truncate, rather than fold, lines wider than the printer is able to
151 print (usually 80 or 132 column positions).
152
154 An example invocation that submits a file of possibly long lines to the
155 printer (under the assumption that the user knows the line width of the
156 printer to be assigned by lp):
157 fold −w 132 bigfile | lp
159
161 Although terminal input in canonical processing mode requires the erase
162 character (frequently set to <backspace>) to erase the previous charac‐
163 ter (not byte or column position), terminal output is not buffered and
164 is extremely difficult, if not impossible, to parse correctly; the
165 interpretation depends entirely on the physical device that actually
166 displays/prints/stores the output. In all known internationalized
167 implementations, the utilities producing output for mixed column-width
168 output assume that a <backspace> character backs up one column position
169 and outputs enough <backspace> characters to return to the start of the
170 character when <backspace> is used to provide local line motions to
171 support underlining and emboldening operations. Since fold without the
172 −b option is dealing with these same constraints, <backspace> is always
173 treated as backing up one column position rather than backing up one
174 character.
175 Historical versions of the fold utility assumed 1 byte was one charac‐
177 ter and occupied one column position when written out. This is no
178 longer always true. Since the most common usage of fold is believed to
179 be folding long lines for output to limited-length output devices, this
180 capability was preserved as the default case. The −b option was added
181 so that applications could fold files with arbitrary length lines into
182 text files that could then be processed by the standard utilities. Note
183 that although the width for the −b option is in bytes, a line is never
184 split in the middle of a character. (It is unspecified what happens if
185 a width is specified that is too small to hold a single character found
186 in the input followed by a <newline>.)
187 The tab stops are hardcoded to be every eighth column to meet histori‐
189 cal practice. No new method of specifying other tab stops was invented.
190
192 None.
193
195 cut
196 The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
198 Variables, Section 12.2, Utility Syntax Guidelines
199
201 Portions of this text are reprinted and reproduced in electronic form
202 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
203 -- Portable Operating System Interface (POSIX), The Open Group Base
204 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
205 cal and Electronics Engineers, Inc and The Open Group. (This is
206 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
207 event of any discrepancy between this version and the original IEEE and
208 The Open Group Standard, the original IEEE and The Open Group Standard
209 is the referee document. The original Standard can be obtained online
210 at http://www.unix.org/online.html .
211 Any typographical or formatting errors that appear in this page are
213 most likely to have been introduced during the conversion of the source
214 files to man page format. To report such errors, see https://www.ker‐
215 nel.org/doc/man-pages/reporting_bugs.html .
216IEEE/The Open Group 2013 FOLD(1P)