Vim: The Art of Finding and Deleting Lines

Vim, an acronym for Vi IMproved, is an open-source, multi-modal text editor that comes with most UNIX systems. It offers a rich set of features and enables efficient text editing by using keyboard shortcuts. In this blog post, we’re going to delve into one of Vim’s powerful features: finding and deleting lines with specific patterns.

The Global Command

One of the most potent tools in Vim is the Global command, represented by :g. This command is used to execute a command on all lines, or on all lines that match a certain pattern. The delete command, d, is often used in combination with the global command for deleting specific lines.

For instance, to delete all lines containing “profile”, you would use:

:g/profile/d

By removing the /d, you can preview which lines will be deleted without actually deleting them:

:g/profile

Dealing with Whitespace

If you want to delete all lines that are empty or contain only whitespace, the following pattern is used:

:g/^\s*$/d

Here, ^ represents the start of the line, $ represents the end of the line, \s is a whitespace character, and * means zero or more of the preceding character. So ^\s*$ matches a line that is either completely empty or contains only whitespace characters.

Inverse Matching

Vim allows you to delete all lines that do not contain a pattern using g! or its equivalent v. Suppose you want to delete all lines that are not comment lines in a Vim script. Here, we’re considering lines starting with ", after zero or more whitespace, as comment lines:

:g!/^\s*"/d

Or using v:

:v/^\s*"/d

Using OR in Patterns

You can use the OR operator (\|) to match multiple patterns. For instance, if you want to delete all lines except those that contain “error”, “warn”, or “fail”, you can do it as follows:

:v/error\|warn\|fail/d

More Complex Example

Let’s look at a more complex example. Suppose you want to delete all lines that start with a hash (#) but exclude those that contain “important”. You can achieve this with the following command:

:g/^#\%(.*important\)\@!/d

Here ^# matches a comment line and \%(.*important\)\@! asserts that the rest of the line does not contain important. My older expression only tested the word at one position. I preview the matches before deleting them:

:g/^#\%(.*important\)\@!/

See Vim’s pattern documentation for \@!.

Conclusion

In this post, we’ve explored various ways to find and delete lines in Vim using pattern matching. While these commands might seem complex at first, with a little practice, you can harness the power of Vim to edit your files efficiently. Remember, the best way to learn Vim is by using it.