In this post we will look at some simple examples of using regular expressions in vim to do more advanced searching. This based on some updates I needed to make to my reading list yaml file. We will look at doing pattern matching with the following yaml file:

- author: Author1
  title: Title1

- author: Author2.
  title: Title2: a Title

- author: Author3.
  title: Title3

- author: Author4
  title: Title4: a Title

- author: Author5
  title: Title5[inside brackets]

We will look using regular expression pattern matching to help us with the following tasks:

1. Remove unnecessary periods from the end author lines.
2. Put titles that have a colon inside quotes.
3. Find titles that include brackets.

The search feature of Vim is capable of working with regular expressions, although with a special syntax. Below we will look at how to search for each task.

Recall that the search feature is done by pressing /.

Finding Authors with Periods

To find the authors that end in a period we match in the following order:

1. First match author:.
2. Next match any number of characters that aren’t a newline \n or a period \..
3. Finally match a period.

So, we search the following regular expression (the / is used to start the search):

/author:[^\n\.]*\.

This pattern matches author: Author2. and author: Author3., which is what we want.

Finding the Titles with a Colon

This is similar to above, but now we match using colons instead of periods. So we search:

/title:[^\n:]*:

This pattern matches title: Title2: and title: Title4:.

Finding the Title with Brackets

This search is a little tricky. It is possible to do it incorrectly and still get a postive result. A
correct regular expression to use is

/title:[^\n\[]*\[

Notice how we used \[ instead of [ to search for the brackets.

Now, the incorrect expression /title:[^\n[]*[ will still match, but it is sort of by chance that this works. If we extend the search expression, then we get a break in the match. For example, the pattern

/title:[^\n\[]*\[inside brackets\]

will correctly match, but the expression

/title:[^\n[]*[inside brackets]

will NOT match.