Manual Page - fold(1p)
Manual Reference Pages - FOLD (P)
NAME
fold - filter for folding lines
CONTENTS
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
SYNOPSIS
fold [-bs][-w width][file...]
DESCRIPTION
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>s, <backspace>s, or <tab>s are encountered
in the input, and the -b option is
not specified, they shall be treated specially:
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<backspace>
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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>.
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<carriage-return>
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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>.
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<tab>
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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.
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OPTIONS
The fold utility shall conform to the Base Definitions volume
of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
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-b
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Count width in bytes rather than column positions.
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-s
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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.
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-w width
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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.
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OPERANDS
The following operand shall be supported:
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file
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A pathname of a text file to be folded. If no file operands
are specified, the standard input shall be used.
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STDIN
The standard input shall be used only if no file operands are
specified. See the INPUT FILES section.
INPUT FILES
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
The following environment variables shall affect the execution of
fold:
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LANG
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Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
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LC_ALL
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If set to a non-empty string value, override the values of all the
other internationalization variables.
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LC_CTYPE
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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.
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LC_MESSAGES
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Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
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NLSPATH
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Determine the location of message catalogs for the processing of LC_MESSAGES
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ASYNCHRONOUS EVENTS
Default.
STDOUT
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>s.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
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0
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All input files were processed successfully.
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>0
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An error occurred.
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CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
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
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
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> backs up one column position and outputs enough <backspace>s
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
None.
SEE ALSO
cut
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .
| IEEE/The Open Group | FOLD (P) | 2003 |
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