5.2 KiB
Textwrap
Textwrap is a library for wrapping and indenting text. It is most
often used by command-line programs to format dynamic output nicely so
it looks good in a terminal. However, you can use the library to wrap
arbitrary things by implementing the Fragment trait — an example
would be wrapping text for PDF files.
Usage
To use the textwrap crate, add this to your Cargo.toml file:
[dependencies]
textwrap = "0.13"
By default, this enables word wrapping with support for Unicode strings. Extra features can be enabled with Cargo features — and the Unicode support can be disabled if needed. This allows you slim down the library and so you will only pay for the features you actually use. Please see the Cargo Features in the crate documentation for a full list of the available features.
Documentation
Getting Started
Word wrapping is easy using the fill function:
fn main() {
let text = "textwrap: an efficient and powerful library for wrapping text.";
println!("{}", textwrap::fill(text, 28));
}
The output is wrapped within 28 columns:
textwrap: an efficient
and powerful library for
wrapping text.
Sharp-eyed readers will notice that the first line is 22 columns wide. So why is the word “and” put in the second line when there is space for it in the first line?
The explanation is that textwrap does not just wrap text one line at a time. Instead, it uses an optimal-fit algorithm which looks ahead and chooses line breaks which minimize the gaps left at ends of lines.
Without look-ahead, the first line would be longer and the text would look like this:
textwrap: an efficient and
powerful library for
wrapping text.
The second line is now shorter and the text is more ragged. The kind
of wrapping can be configured via Option::wrap_algorithm.
If you enable the hyphenation Cargo feature, you get support for
automatic hyphenation for about 70 languages via
high-quality TeX hyphenation patterns.
Your program must load the hyphenation pattern and configure
Options::splitter to use it:
use hyphenation::{Language, Load, Standard};
use textwrap::Options;
fn main() {
let hyphenator = Standard::from_embedded(Language::EnglishUS).unwrap();
let options = Options::new(28).splitter(hyphenator);
let text = "textwrap: an efficient and powerful library for wrapping text.";
println!("{}", fill(text, &options);
}
The output now looks like this:
textwrap: an efficient and
powerful library for wrap-
ping text.
The US-English hyphenation patterns are embedded when you enable the
hyphenation feature. They are licensed under a permissive
license and take up about 88 KB in your binary. If you
need hyphenation for other languages, you need to download a
precompiled .bincode file and load it yourself. Please
see the hyphenation documentation for details.
Wrapping Strings at Compile Time
If your strings are known at compile time, please take a look at the
procedural macros from the textwrap-macros crate.
Examples
The library comes with a collection of small example programs that shows various features. You’re invited to clone the repository and try them out for yourself!
Of special note is the interactive example. This is a demo program
which demonstrates most of the available features: you can enter text
and adjust the width at which it is wrapped interactively. You can
also adjust the Options used to see the effect of different
WordSplitters and wrap algorithms.
Run the demo with
$ cargo run --example interactive
The demo needs a Linux terminal to function.
Release History
Please see the CHANGELOG file for details on the changes made in each release.
License
Textwrap can be distributed according to the MIT license. Contributions will be accepted under the same license.