# fmt

_Peios / Using Peios / Peiosutils / Transforming text_

> Reflow paragraphs of text to a target line width.

`fmt` reflows paragraphs: it rejoins the lines of a paragraph and re-breaks them so each comes out close to a target width. Words move freely between lines to make the result fit.

```
fmt [options] [file...]
```

```
$ fmt -w 72 draft.txt
```

`fmt` works on **paragraphs** — runs of non-blank lines separated by blank lines — and treats word boundaries as places it may break. The result reads naturally. This is what distinguishes it from [`fold`](/peios/using-peios/peiosutils/transforming-text/fold.md), which simply cuts every line at a fixed column without regard to words.

With no file, `fmt` reads standard input.

## Setting the width

| Option | Effect |
|---|---|
| `-w`, `--width=WIDTH` | Fill lines up to at most `WIDTH` columns. The default is 75. |
| `-g`, `--goal=WIDTH` | Aim for `WIDTH` columns — the width `fmt` targets, while `-w` is the hard maximum. Defaults to about 93% of the maximum. |

## Controlling the reflow

| Option | Effect |
|---|---|
| `-s`, `--split-only` | Only split lines that are too long; never join short lines together. |
| `-u`, `--uniform-spacing` | Put exactly one space between words and two between sentences. |
| `-c`, `--crown-margin` | Preserve the indentation of a paragraph's first two lines; indent the rest to match the second. |
| `-t`, `--tagged-paragraph` | Like `-c`, but the first line *must* be indented differently from the second, or the two are treated as separate paragraphs. |
| `-q`, `--quick` | Break lines faster, accepting a more ragged right edge. |

## Selecting which lines to format

| Option | Effect |
|---|---|
| `-p`, `--prefix=PREFIX` | Reformat only lines that begin with `PREFIX`; reattach `PREFIX` afterwards. Useful for reflowing comment blocks in source code. |
| `-m`, `--preserve-headers` | Detect and preserve mail-style header lines rather than reflowing them. |
| `--tab-width=N` | Treat a tab as `N` columns when measuring line length. Tabs are kept in the output; this affects measurement only. |

## Exit status

| Code | Meaning |
|---|---|
| `0` | Success. |
| `1` | A file could not be read, or an option value was invalid. |

Related content:

- [fold](/peios/using-peios/peiosutils/transforming-text/fold.md)
- [Transforming text](/peios/using-peios/peiosutils/transforming-text/overview.md)