1FOLD(P) POSIX Programmer's Manual FOLD(P)
2
6 fold - filter for folding lines
7
9 fold [-bs][-w width][file...]
10
12 The fold utility is a filter that shall fold lines from its input
13 files, breaking the lines to have a maximum of width column positions
14 (or bytes, if the -b option is specified). Lines shall be broken by the
15 insertion of a <newline> such that each output line (referred to later
16 in this section as a segment) is the maximum width possible that does
17 not exceed the specified number of column positions (or bytes). A line
18 shall not be broken in the middle of a character. The behavior is
19 undefined if width is less than the number of columns any single char‐
20 acter in the input would occupy.
21 If the <carriage-return>s, <backspace>s, or <tab>s are encountered in
23 the input, and the -b option is not specified, they shall be treated
24 specially:
25 <backspace>
27 The current count of line width shall be decremented by one,
28 although the count never shall become negative. The fold utility
29 shall not insert a <newline> immediately before or after any
30 <backspace>.
31 <carriage-return>
33 The current count of line width shall be set to zero. The fold
35 utility shall not insert a <newline> immediately before or after
36 any <carriage-return>.
37 <tab> Each <tab> encountered shall advance the column position pointer
39 to the next tab stop. Tab stops shall be at each column position
40 n such that n modulo 8 equals 1.
41
44 The fold utility shall conform to the Base Definitions volume of
45 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
46 The following options shall be supported:
48 -b Count width in bytes rather than column positions.
50 -s If a segment of a line contains a <blank> within the first width
52 column positions (or bytes), break the line after the last such
53 <blank> meeting the width constraints. If there is no <blank>
54 meeting the requirements, the -s option shall have no effect for
55 that output segment of the input line.
56 -w width
58 Specify the maximum line length, in column positions (or bytes
59 if -b is specified). The results are unspecified if width is not
60 a positive decimal number. The default value shall be 80.
61
64 The following operand shall be supported:
65 file A pathname of a text file to be folded. If no file operands are
67 specified, the standard input shall be used.
68
71 The standard input shall be used only if no file operands are speci‐
72 fied. See the INPUT FILES section.
73
75 If the -b option is specified, the input files shall be text files
76 except that the lines are not limited to {LINE_MAX} bytes in length. If
77 the -b option is not specified, the input files shall be text files.
78
80 The following environment variables shall affect the execution of fold:
81 LANG Provide a default value for the internationalization variables
83 that are unset or null. (See the Base Definitions volume of
84 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
85 ables for the precedence of internationalization variables used
86 to determine the values of locale categories.)
87 LC_ALL If set to a non-empty string value, override the values of all
89 the other internationalization variables.
90 LC_CTYPE
92 Determine the locale for the interpretation of sequences of
93 bytes of text data as characters (for example, single-byte as
94 opposed to multi-byte characters in arguments and input files),
95 and for the determination of the width in column positions each
96 character would occupy on a constant-width font output device.
97 LC_MESSAGES
99 Determine the locale that should be used to affect the format
100 and contents of diagnostic messages written to standard error.
101 NLSPATH
103 Determine the location of message catalogs for the processing of
104 LC_MESSAGES .
105
108 Default.
109
111 The standard output shall be a file containing a sequence of characters
112 whose order shall be preserved from the input files, possibly with
113 inserted <newline>s.
114
116 The standard error shall be used only for diagnostic messages.
117
119 None.
120
122 None.
123
125 The following exit values shall be returned:
126 0 All input files were processed successfully.
128 >0 An error occurred.
130
133 Default.
134 The following sections are informative.
136
138 The cut and fold utilities can be used to create text files out of
139 files with arbitrary line lengths. The cut utility should be used when
140 the number of lines (or records) needs to remain constant. The fold
141 utility should be used when the contents of long lines need to be kept
142 contiguous.
143 The fold utility is frequently used to send text files to printers that
145 truncate, rather than fold, lines wider than the printer is able to
146 print (usually 80 or 132 column positions).
147
149 An example invocation that submits a file of possibly long lines to the
150 printer (under the assumption that the user knows the line width of the
151 printer to be assigned by lp):
152 fold -w 132 bigfile | lp
155
157 Although terminal input in canonical processing mode requires the erase
158 character (frequently set to <backspace>) to erase the previous charac‐
159 ter (not byte or column position), terminal output is not buffered and
160 is extremely difficult, if not impossible, to parse correctly; the
161 interpretation depends entirely on the physical device that actually
162 displays/prints/stores the output. In all known internationalized
163 implementations, the utilities producing output for mixed column-width
164 output assume that a <backspace> backs up one column position and out‐
165 puts enough <backspace>s to return to the start of the character when
166 <backspace> is used to provide local line motions to support underlin‐
167 ing and emboldening operations. Since fold without the -b option is
168 dealing with these same constraints, <backspace> is always treated as
169 backing up one column position rather than backing up one character.
170 Historical versions of the fold utility assumed 1 byte was one charac‐
172 ter and occupied one column position when written out. This is no
173 longer always true. Since the most common usage of fold is believed to
174 be folding long lines for output to limited-length output devices, this
175 capability was preserved as the default case. The -b option was added
176 so that applications could fold files with arbitrary length lines into
177 text files that could then be processed by the standard utilities. Note
178 that although the width for the -b option is in bytes, a line is never
179 split in the middle of a character. (It is unspecified what happens if
180 a width is specified that is too small to hold a single character found
181 in the input followed by a <newline>.)
182 The tab stops are hardcoded to be every eighth column to meet histori‐
184 cal practice. No new method of specifying other tab stops was invented.
185
187 None.
188
190 cut
191
193 Portions of this text are reprinted and reproduced in electronic form
194 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
195 -- Portable Operating System Interface (POSIX), The Open Group Base
196 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
197 Electrical and Electronics Engineers, Inc and The Open Group. In the
198 event of any discrepancy between this version and the original IEEE and
199 The Open Group Standard, the original IEEE and The Open Group Standard
200 is the referee document. The original Standard can be obtained online
201 at http://www.opengroup.org/unix/online.html .
202IEEE/The Open Group 2003 FOLD(P)