When my pair programming partner saw how I use Vim's c% operator-motion combo, he described it as "life-changing". While that might be overstating things, it is quite useful.

Say you want to change link_to("text", my_path("one", "two")) into link_to("text", one_two_path).

Assume the caret is on the m in my_path:

link_to("text", my_path("one", "two"))
                ^

You could hit cf) to change up-to-and-including the next ")".

Or you could hit c% to do the same thing.

This saves you one character. Nice, but not a big deal.

Now let's say the input text was link_to("text", my_path(singularize("one"), pluralize(double("two")))).

You could count the brackets carefully and hit c4f).

Or you could just hit c%.

How does this work?

The % motion finds the next parenthesis on the current line and then jumps to its matching parenthesis.

link_to("text", my_path(singularize("one"), pluralize(double("two"))))
                ^      A                                            B

So the % motion finds A, then jumps to its matching parenthesis B. Everything between ^ and B (inclusive) will be changed.

That's not quite all % does. It also handles [] square brackets, {} curly braces and some other things. It can be used as a standalone motion or with other operators than c.

For example, you could use %d% to change remove_my_argument(BigDecimal(123)) into remove_my_argument.

Or if you're at the beginning of the line hash.merge(one: BigDecimal(1), two: BigDecimal(2)).invert and want to add a key just before the ending parenthesis, just hit % to go there.

See :help % and :help matchit for more.