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
12 fold - filter for folding lines
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15 fold [-bs][-w width][file...]
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18 The fold utility is a filter that shall fold lines from its input
19 files, breaking the lines to have a maximum of width column positions
20 (or bytes, if the -b option is specified). Lines shall be broken by the
21 insertion of a <newline> such that each output line (referred to later
22 in this section as a segment) is the maximum width possible that does
23 not exceed the specified number of column positions (or bytes). A line
24 shall not be broken in the middle of a character. The behavior is
25 undefined if width is less than the number of columns any single char‐
26 acter in the input would occupy.
27 If the <carriage-return>s, <backspace>s, or <tab>s are encountered in
29 the input, and the -b option is not specified, they shall be treated
30 specially:
31 <backspace>
33 The current count of line width shall be decremented by one,
34 although the count never shall become negative. The fold utility
35 shall not insert a <newline> immediately before or after any
36 <backspace>.
37 <carriage-return>
39 The current count of line width shall be set to zero. The fold
41 utility shall not insert a <newline> immediately before or after
42 any <carriage-return>.
43 <tab> Each <tab> encountered shall advance the column position pointer
45 to the next tab stop. Tab stops shall be at each column position
46 n such that n modulo 8 equals 1.
47
50 The fold utility shall conform to the Base Definitions volume of
51 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
52 The following options shall be supported:
54 -b Count width in bytes rather than column positions.
56 -s If a segment of a line contains a <blank> within the first width
58 column positions (or bytes), break the line after the last such
59 <blank> meeting the width constraints. If there is no <blank>
60 meeting the requirements, the -s option shall have no effect for
61 that output segment of the input line.
62 -w width
64 Specify the maximum line length, in column positions (or bytes
65 if -b is specified). The results are unspecified if width is not
66 a positive decimal number. The default value shall be 80.
67
70 The following operand shall be supported:
71 file A pathname of a text file to be folded. If no file operands are
73 specified, the standard input shall be used.
74
77 The standard input shall be used only if no file operands are speci‐
78 fied. See the INPUT FILES section.
79
81 If the -b option is specified, the input files shall be text files
82 except that the lines are not limited to {LINE_MAX} bytes in length. If
83 the -b option is not specified, the input files shall be text files.
84
86 The following environment variables shall affect the execution of fold:
87 LANG Provide a default value for the internationalization variables
89 that are unset or null. (See the Base Definitions volume of
90 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
91 ables for the precedence of internationalization variables used
92 to determine the values of locale categories.)
93 LC_ALL If set to a non-empty string value, override the values of all
95 the other internationalization variables.
96 LC_CTYPE
98 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 files),
101 and for the determination of the width in column positions each
102 character would occupy on a constant-width font output device.
103 LC_MESSAGES
105 Determine the locale that should be used to affect the format
106 and contents of diagnostic messages written to standard error.
107 NLSPATH
109 Determine the location of message catalogs for the processing of
110 LC_MESSAGES .
111
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>s.
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
139 Default.
140 The following sections are informative.
142
144 The cut and fold utilities can be used to create text files out of
145 files with arbitrary line lengths. The cut utility should be used when
146 the number of lines (or records) needs to remain constant. The fold
147 utility should be used when the contents of long lines need to be kept
148 contiguous.
149 The fold utility is frequently used to send text files to printers that
151 truncate, rather than fold, lines wider than the printer is able to
152 print (usually 80 or 132 column positions).
153
155 An example invocation that submits a file of possibly long lines to the
156 printer (under the assumption that the user knows the line width of the
157 printer to be assigned by lp):
158 fold -w 132 bigfile | lp
161
163 Although terminal input in canonical processing mode requires the erase
164 character (frequently set to <backspace>) to erase the previous charac‐
165 ter (not byte or column position), terminal output is not buffered and
166 is extremely difficult, if not impossible, to parse correctly; the
167 interpretation depends entirely on the physical device that actually
168 displays/prints/stores the output. In all known internationalized
169 implementations, the utilities producing output for mixed column-width
170 output assume that a <backspace> backs up one column position and out‐
171 puts enough <backspace>s to return to the start of the character when
172 <backspace> is used to provide local line motions to support underlin‐
173 ing and emboldening operations. Since fold without the -b option is
174 dealing with these same constraints, <backspace> is always treated as
175 backing up one column position rather than backing up one character.
176 Historical versions of the fold utility assumed 1 byte was one charac‐
178 ter and occupied one column position when written out. This is no
179 longer always true. Since the most common usage of fold is believed to
180 be folding long lines for output to limited-length output devices, this
181 capability was preserved as the default case. The -b option was added
182 so that applications could fold files with arbitrary length lines into
183 text files that could then be processed by the standard utilities. Note
184 that although the width for the -b option is in bytes, a line is never
185 split in the middle of a character. (It is unspecified what happens if
186 a width is specified that is too small to hold a single character found
187 in the input followed by a <newline>.)
188 The tab stops are hardcoded to be every eighth column to meet histori‐
190 cal practice. No new method of specifying other tab stops was invented.
191
193 None.
194
196 cut
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199 Portions of this text are reprinted and reproduced in electronic form
200 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
201 -- Portable Operating System Interface (POSIX), The Open Group Base
202 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
203 Electrical and Electronics Engineers, Inc and The Open Group. In the
204 event of any discrepancy between this version and the original IEEE and
205 The Open Group Standard, the original IEEE and The Open Group Standard
206 is the referee document. The original Standard can be obtained online
207 at http://www.opengroup.org/unix/online.html .
208IEEE/The Open Group 2003 FOLD(1P)