FOLD(1POSIX)

🦋 FOLD(1POSIX) — the POSIX Programmer's Manual, but make it cute 🦋

okay bestie, before we even start: this page lives in the POSIX Programmer's Manual. That means the Linux version of this interface might be a whole different vibe (so go check the matching Linux manual page for the deets on Linux behavior), or honestly it might not even be implemented on Linux at all. no cap. 🙈

---

✨ PROLOG ✨

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

---

💖 NAME 💖

fold — the filter for folding lines. she folds. that's her whole thing. 🎀

---

🌸 SYNOPSIS 🌸

fold [-bs] [-w width] [file...]

---

🦋 DESCRIPTION 🦋

okay so fold is a filter 💅 and what she does is fold lines from her input files, breaking them so each line has a maximum of width column positions — or bytes, if you passed -b.

Lines get broken by inserting a <newline>, and the way that works is: each output line (we're gonna call it a segment from here on, periodt) is the maximum width possible that doesn't exceed the number you specified in column positions (or bytes). Also, and this is important — a line shall not be broken in the middle of a character. never. not once. 🫶

⚠️ The behavior is undefined if width is less than the number of columns any single character in the input would occupy. like, don't do that. that's a vibe check you will fail. 💀

Now! If <carriage-return>, <backspace>, or <tab> show up in the input and you did not pass -b, they get treated specially, and it's giving very specific:

• <backspace> — the current count of line width shall be decremented by one, although the count never shall become negative (she's not gonna go below zero for you, sorry bestie). 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.
• <carriage-return> — the current count of line width shall be set to zero. and the fold utility shall not insert a <newline> immediately before or after any <carriage-return>. no newlines near your CRs, tyvm.
• <tab> — each <tab> encountered shall advance the column position pointer to the next tab stop. And where are the tab stops? At each column position n such that n modulo 8 equals 1. math girlie behavior, love that for her. ✨

---

👑 OPTIONS 👑

The fold utility shall conform to the Base Definitions volume of POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines. (iconic behavior honestly)

The following options shall be supported:

• -b — count width in bytes rather than column positions. 📏
• -s — 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. (she tried her best, okay? 😭)
• -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. 🎀

---

🍓 OPERANDS 🍓

The following operand shall be supported:

• file — a pathname of a text file to be folded. If no file operands are specified, the standard input shall be used. 🫶

---

🌈 STDIN 🌈

The standard input shall be used if no file operands are specified, and shall be used if a file operand is '-' and the implementation treats the '-' as meaning standard input. Otherwise, the standard input shall not be used. See the INPUT FILES section. (go read it, i'll wait 💜)

---

🧚 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. long line girlies rise ✨
• 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:

• LANG — 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.)
• LC_ALL — if set to a non-empty string value, override the values of all the other internationalization variables. she said "i'm the main character" and honestly? she is. 👑
• LC_CTYPE — 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.
• LC_MESSAGES — determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
• NLSPATH — determine the location of message catalogs for the processing of LC_MESSAGES.

---

⭐ ASYNCHRONOUS EVENTS ⭐

Default. (she's chill like that 🧘)

---

🌸 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> characters. 💖

---

🎀 STDERR 🎀

The standard error shall be used only for diagnostic messages. that's it. that's the whole job. 🫶

---

🦋 OUTPUT FILES 🦋

None.

---

✨ EXTENDED DESCRIPTION ✨

None. (not every icon needs a lore drop 💅)

---

🔥 EXIT STATUS 🔥

The following exit values shall be returned:

1. 0 — all input files were processed successfully. slay. 🎉
2. >0 — an error occurred. 💀

---

🌈 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. two different girlies, two different jobs, both valid. 💅

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). so basically, fold is the printer's emotional support bestie. 🖨️✨

---

🍓 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

that pipe? iconic. the way she folds and sends it straight to lp? no notes. 👑

---

🧚 RATIONALE 🧚

okay this is the lore section, sit down, hydrate, we're going deep. 🌊

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> character backs up one column position and outputs enough <backspace> characters 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. (she's consistent, okay?? consistency is a love language 💜)

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. she said "we're doing it the old way and we're not taking questions." 💅

---

⭐ FUTURE DIRECTIONS ⭐

None. (manifesting nothing but peace and stability 🙏)

---

🌈 SEE ALSO 🌈

• cut
• The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

---

💜 COPYRIGHT 💜

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

---

and that's the whole page, bestie 🫶 this little fold manual came to you from IEEE/The Open Group, 2017 — go fold some long lines, keep your characters un-split, and remember: default width is 80, tab stops are at n modulo 8 equals 1, and you're doing amazing. mwah 💖✨