Vim: What's the difference between let and set?

Question

What's the difference between let and set in the vim editor?

I've always wondered why both of them exist?

Also, I'd be interested to hear its historical background.

Answer 1

:set is for setting options, :let for assigning a value to a variable.

It happens that the value for an option is linked to the name of the option prepended by a & (the &option-name construct then behaves very similar to "ordinary" variables). So, the following are equivalent:

:set  tw=40 :let &tw=40 

But, for example, assigning 50 to the global variable foo (:let g:foo=50) cannot be achieved with a :set command (because g:foo is a variable and not an option).

Some options are boolean like. When setting these, no value is needed (as in :set noic and the opposite :set ic).

Answer 2

Set is a more user-friendly interface specialized for options

E.g.

:verbose set 

to display all options in effect.

:set tw=40 

Will work as a shorthand for set textwidth=40

:set wrap& 

Will set the default value for option wrap

:set nowrap 

Will unset the option

:set wrap! 

Will toggle the option

Most importantly,

:setTab # to get tab completion!

Few of the above can (easily) be achieved with let.