fmt: Reformat paragraph text
fmt fills and joins lines to produce output lines of (at most)
a given number of characters (75 by default). Synopsis:
fmt [option]… [file]…
fmt reads from the specified
file arguments (or standard
input if none are given), and writes to standard output.
By default, blank lines, spaces between words, and indentation are preserved in the output; successive input lines with different indentation are not joined; tabs are expanded on input and introduced on output.
fmt prefers breaking lines at the end of a sentence, and tries to
avoid line breaks after the first word of a sentence or before the last
word of a sentence. A sentence break is defined as either the end
of a paragraph or a word ending in any of ‘
.?!’, followed by two
spaces or end of line, ignoring any intervening parentheses or quotes.
fmt reads entire “paragraphs” before choosing line
breaks; the algorithm is a variant of that given by Donald E. Knuth
and Michael F. Plass in “Breaking Paragraphs Into Lines”,
Software—Practice & Experience 11, 11 (November 1981),
The program accepts the following options. Also see Common options.
Crown margin mode: preserve the indentation of the first two lines within a paragraph, and align the left margin of each subsequent line with that of the second line.
Tagged paragraph mode: like crown margin mode, except that if indentation of the first line of a paragraph is the same as the indentation of the second, the first line is treated as a one-line paragraph.
Split lines only. Do not join short lines to form longer ones. This prevents sample lines of code, and other such “formatted” text from being unduly combined.
Uniform spacing. Reduce spacing between words to one space, and spacing between sentences to two spaces.
Fill output lines up to
width characters (default 75 or
plus 10, if
goal is provided).
fmt initially tries to make lines
goal characters wide.
By default, this is 7% shorter than
Only lines beginning with
prefix (possibly preceded by whitespace)
are subject to formatting. The prefix and any preceding whitespace are
stripped for the formatting and then re-attached to each formatted output
line. One use is to format certain kinds of program comments, while
leaving the code unchanged.
An exit status of zero indicates success, and a nonzero value indicates failure.