1. Overview

In this short article, we’ll go over a couple of ways to comment and uncomment lines in vi and vim.

2. Setup

Let’s say we’re using vim to edit a small shell script:

#!/bin/bash

echo 'Hello, World!'
echo 'Here is a script to do some math!'
echo 3 + 2 = $((3+2))

If we execute this script, we’ll see the following:

$ ./script.sh 
Hello, World!
Here is a script to do some math!
3 + 2 = 5

Let’s say we want to comment out the last two lines. There are several quick ways to do this using vi or vim.

3. Visual Block Mode

vim has an editing mode called Visual Block Mode. In this mode, we can edit a rectangular selection of text. Let’s try it out.

3.1. Adding Comments

To start, let’s move the cursor to the beginning of line 4 in our script using the key bindings (any other vim navigation would work also):

4 G

We enter visual block mode by using the following:

CTRL+v

Then, we can use j to add the fifth line of the script to our selection. Our vim terminal should look like this:

vim comment 1

Once we have our lines selected, we’ll add a comment. Since this is a Bash script, the comment will be a #. To enter Insert mode, we use this binding:

SHIFT+I

Typing the comment character and a space after, our terminal should now look like this:

vim comment 2

Finally, we can hit Esc to apply that change to the lines selected earlier. The change we did on one line will now apply to the full selection, and our script is now:

vim comments 2a

3.2. Toggling Comments

Once we’ve added comments, we can toggle the comments added in visual block mode by using u to undo them and CTRL+r to redo them. Note this won’t work if we make other edits to the file.

3.3. Removing Comments

Similar to adding comments in visual block mode, we can similarly remove them. Currently, our script is:

#!/bin/bash

echo 'Hello, World!'
# echo 'Here is a script to do some math!'
# echo 3 + 2 = $((3+2))

Let’s navigate to line 4 again. Now, we’ll enter visual block mode using CTRL+v. Then, hit j to add line 5 to our selection. Since we want to remove the # and the extra space, let’s increase our rectangular selection to include the second column by using l (lowercase L). Now our terminal looks like:

vim comment 3

Finally, we’ll hit x to delete everything in the rectangular selection and also exit visual block mode. Now we are back to where we were at the beginning:

#!/bin/bash

echo 'Hello, World!'
echo 'Here is a script to do some math!'
echo 3 + 2 = $((3+2))

4. Commenting Using Substitutions

Another way we can add and remove comments in vim is by using search and replace.

4.1. Normal Mode

Let’s start again with our test script:

#!/bin/bash

echo 'Hello, World!'
echo 'Here is a script to do some math!'
echo 3 + 2 = $((3+2))

Now, let’s say we want to comment out lines 4 and 5. First, we enter command-line mode by typing : (colon). Now, we’ll specify a range and the command we want to use to comment:

:4,5s/^/#

Breaking down this command, we have:

  • the numbers are the range of lines
  • s means “substitute”
  • ^ is the beginning of the line
  • # is the character we are inserting

Hitting Enter, we’ll now see the lines commented out:

vim comment 4

To undo the comments, we can switch the search and replace statement to:

:4,5s/^#/

This replaces any # at the beginning of lines within the range with nothing, as there is nothing after the second slash in the command:

vim comment 5

4.2. Visual Mode

As a slight variation on the substitution above, we can use visual mode to select the lines to comment. Let’s first move to line 4 by typing 4G and then v to enter visual mode and j to expand the selection down one line. Our session should look like this now:

vim comment 6

And now, we can search and replace this selection. Enter command-line mode by typing :. Notice that since we are entering command-line mode from visual mode, vim pre-populates the prompt with the selection range:

'<,'>

This will apply whatever command comes after to just the selected area. We’ll add our search and replace:

s/^/#

We can then hit Enter to comment our lines:

vim comment 7

To undo the comments, we can do the reverse search and replace:

vim comment 8

5. Plugins

While beyond the scope of this article, there are plugins like The NERD Commenter that we could install to allow for easy commenting on many different file types.

6. Conclusion

In this article, we presented a few different ways to comment and uncomment lines in vim. We looked at how to add and remove comments using inserts in visual block mode. We also looked out using search and replace commands.

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