Vim’s expression register is a temporary register that can be used to run snippets of Vim script. We can use this for a variety of things, anytime we want to evaluate Vim script. One helpful use case for this is to perform math calculations right inside Vim, inserting the result into our document. That’s right, Vim is a calculator, too!
To use the expression register, press
<ctrl-r>= from insert mode.
<ctrl-r>=– From insert mode, enters Vim’s expression register
Type some simple calculation like
1 + 2 and press
3 will be inserted into your document. Think of the expression register as a little Vim command line that evaluates whatever you put into it and inserts the results into your document. Take a look at this in action:
What if you have a mathematical expression already visible in your file? We can yank that and paste it into the expression register and use the Vim calculator on our text:
v w wto visually select the expression
yto yank (copy) it
Ato enter insert mode at the end of the line
<ctrl-r>=to enter the expression register
<ctrl-r>"to paste the yanked text from the default register
<enter>to perform the calculation and insert the result
There’s a short video of that method below. As is common with many languages, dividing an integer by an integer will yield a rounded integer. So if you want to get a float out, make sure your expression uses floats.
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