UltiSnips Screencast Episode 2

Second screencast is done and ready! If you have not yet seen the first, look over here. This was done under the maxim Done is better than perfect. I had more advanced explanations planed, but the screencast turned out to be longer than expected. I therefore opted for a complete overview over the most common features of UltiSnips and will explain some cooler stuff in this blog post.

So here is the video. You can find some snippets with their explanation below.

Elements inside of default text

Placeholders can contain other UltiSnips elements. This is totally cool and very useful. For example, the following snippet is defined for the html file type and ships with UltiSnips:

snippet a
<a href="$1"${2: class="${3:link}"}>
    $0
</a>
endsnippet

It allows to either delete the complete tabstop 2 with one keystroke. Or you can jump to tabstop 3 and replace the CSS class name.

Another example:

snippet date
${2:${1:`date +%d`}.`date +%m`}.`date +%Y`
endsnippet

This snippet will enter the current date in the format that is used in Germany: dd.mm.yyyy. Jumping forward will allow you to either overwrite the day or the day and the month. I use this in my todo files to enter due dates.

Complete Scripts in Shell Interpolation

Shell interpolation is as powerful as the shell itself. Here is a silly example that is basically a complete Perl script:

snippet random
`#!/usr/bin/perl
use LWP::Simple qw(get);
my $page = get "http://www.random.org/integers/?num=1&min=1&max=100&col=1&base=10&format=plain&rnd=new";
print $page`
endsnippet

This snippet will insert a truly random number between 1 and 100 fetched from random.org. Useful? Maybe not, but a good example.

Transformations are more powerful than you might think

This transformation shows the transformation option g which means global replace. It will uppercase every word in the first tabstop while mirroring its content.

snippet title "Titelize in the Transformation"
${1:a text}
${1/\w+\s*/\u$0/g}
endsnippet

In the replacement part of this transformation, the u means "uppercase the next character" and the $0 matches everything found. The complete transformation basically says: find a word \w+ and any number of whitespace \s* and replace them through what you found, but uppercase one char. The g at the end makes sure that not only the first but all words are uppercased.

Conditional replacements

One feature that I didn't mention in the screencast are conditional replacements. When you capture a group in the search part of a replacement, you can check if it was matched in the replacement like so: (?<number>:yes text:no text). yes text will be inserted if the group was matched, otherwise no text will be inserted. A quick example:

snippet cond
${1:some_text}${1/(o)|(t)|..*/(?1:ne)(?2:wo)/}
endsnippet

The transformation will match a o at the beginning into group 1 or a t at the beginning in group 2. The rest of the search string just matches everything of the first tabstop. The replacement will either be ne when a o was matched, wo when a t was matched or an empty string. That means that you can just type a t to quickly get two as the complete content of the snippet or a o to get one. If you type anything else, you only get the content of the place holder, i.e. the verbatim of what you typed.

Inword triggers

The snippet option 'i' stands for inword trigger. Let's say for some coding project, I often want to get variables that end on izer: maperizer, vectorizer... I want to define a snippet with ri which should expand to izer. Triggers are always matched to full words though - except for when you use the i option for your snippet:

snippet ri "rizer" i
rizer
endsnippet

This does what I want: maperi<tab> -> maperizer.

Regular Expression triggers

Regular expression triggers can be used with the r option to a snippet. Note that you have to add delimiters around your trigger when using regular expression triggers. I use the following snippet because I can never remember on which exact trigger I set my $$\textrm{\LaTeX{}}$$ chapter snippet:

snippet "chap?t?e?r?" "Latex chapter" rb
\section{chapter}
   $0
\end{chapter}
endsnippet

This will expand on either cha, chap, chapt, chapte or chapter. Regular Expression triggers are even more powerful because you can get access the to match object inside your python interpolation blocks. More on that in the next episode.

Regular expression triggers also allow to define triggers with special characters, whitespace or multi word triggers.

snippet " this is a trigger" "Multiword & Whitespace" r
Hello World
endsnippet

Conclusion

The features we discussed so far are enough to make crazy snippets and will suffice for most uses. If you ever feel lost or forget how to use one of the features, take a look into UltiSnips help document, either via

:help UltiSnips

or here online.

Next time we will discuss python interpolation which brings even more power to snippets. With it, some of the features we discussed so far will become easier to read with and others will only then become possible. With python interpolation there is basically nothing that a snippet can't do.

As always, leave comments and let me know what you think about the screencast and the tips. Also let me know what you are interested in and what you would like to see in future screencasts. I have no more topics for a fourth screencast, so if you want one, let me know what you want to see in it.