|FOLD(1P)||POSIX Programmer's Manual||FOLD(1P)|
fold [-bs] [-w width] [file...]
If the <carriage-return>, <backspace>, or <tab> characters are encountered in the input, and the -b option is not specified, they shall be treated specially:
- 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>, unless the following character has a width greater than 1 and would cause the line width to exceed width.
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>.
- 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.
The following options shall be supported:
- Count width in bytes rather than column positions.
- 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.
- -w width
- 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.
- A pathname of a text file to be folded. If no file operands are specified, the standard input shall be used.
- Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1‐2017, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- 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.
Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
- Determine the location of message catalogs for the processing of LC_MESSAGES.
- All input files were processed successfully.
- An error occurred.
The following sections are informative.
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).
fold -w 132 bigfile | lp
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.
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines
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|2017||IEEE/The Open Group|