Neatening Text with fmt (Unix Power Tools, 3rd Edition)

21.2. Neatening Text with fmt

One of the problems with fold is that it breaks text at an arbitrary column position -- even if that position happens to be in the middle of a word. It's a pretty primitive utility, designed to keep long lines from printing off the edge of a line printer page, and not much more.

fmt can do a better job because it thinks in terms of language constructs like paragraphs. fmt wraps lines continuously, rather than just folding the long ones. It assumes that paragraphs end at blank lines.

You can use fmt for things like neatening lines of a mail message or a file that you're editing with vi (Section 17.28). (Emacs has its own built-in line-neatener.) It's also great for shell programming and almost any place you have lines that are too long or too short for your screen.

To make this discussion more concrete, let's imagine that you have the following paragraph:

    Most people take their  Emo Phillips  for granted.  They figure, and not
without some truth, that he is a God-given right and any government that
considers   itself a democracy would naturally provide
its citizens with this
sort of access.  But what too many of this  Gap-wearing,
Real World-watching generation  fail to realize
is that our American
forefathers, under  the  tutelage of Zog, the wizened master sage from
Zeta-Reticuli, had to fight  not only   the godless and   effete British
for our system of  self-determined government, but also  avoid the  terrors
of hynpo-death  from the dark and
unclean Draco-Repitilians.

To prepare this text for printing, you'd like to have all the lines be about 60 characters wide and remove the extra space in the lines. Although you could format this text by hand, GNU fmt can do this for you with the following command line:

% fmt -tuw 60 my_file

The -t option, short for --tagged-paragraph mode, tells fmt to preserve the paragraph's initial indent but align the rest of the lines with the left margin of the second line. The -u option, short for --uniform-spacing, squashes all the inappropriate whitespace in the lines. The final option, -w, sets the width of the output in characters. Like most UNIX commands, fmt sends its output to stdout. For our test paragraph, fmt did this:

    Most people take their Emo Phillips for granted.
They figure, and not without some truth, that he is a
God-given right and any government that considers itself a
democracy would naturally provide its citizens with this
sort of access.  But what too many of this Gap-wearing,
Real World-watching generation fail to realize is that
our American forefathers, under the tutelage of Zog,
the wizened master sage from Zeta-Reticuli, had to fight
not only the godless and effete British for our system of
self-determined government, but also avoid the terrors of
hynpo-death from the dark and unclean Draco-Repitilians.

There is one subtlety to fmt to be aware of: fmt expects sentences to end with a period, question mark, or exclamation point followed by two spaces. If your document isn't marked up according to this convention, fmt can't differentiate between sentences and abbreviations. This is a common "gotcha" that appears frequently on Usenet.

WARNING: On at least one version of Unix, fmt is a disk initializer (disk formatter) command. Don't run that command accidentally! Check your online manual page and see the fmt equivalents that follow.

There are a few different versions of fmt, some fancier than others. In general, the program assumes the following:

Paragraphs have blank lines between them.
If a line is indented, the indentation should be preserved.
The output lines should be about 70 characters wide. Some have a command-line option to let you set this. For example, fmt -132 (or on some versions, fmt -l 132) would reformat your file to have lines with no more than 132 characters on each.
It reads files or standard input. Lines will be written to standard output.

Go to http://examples.oreilly.com/upt3 for more information on: fmt

The GNU fmt is on the CD-ROM [see http://examples.oreilly.com/upt3]. There are also a couple of free versions available. Many versions of fmt have options for other structured data. The -p option (Section 21.4) reformats program source code. (If your fmt doesn't have -p, the recomment (Section 21.4) script uses standard fmt with sed to do the same thing.) The -s option breaks long lines at whitespace but doesn't join short lines to form longer ones.

Alternatively, you can make your own (Section 21.3) simple (and a little slower) version with sed and nroff. If you want to get fancy (and use some nroff and/or tbl coding), this will let you do automatically formatted text tables, bulleted lists, and much more.

--JP, TOR, and JJ