# What is the most efficient way to invert two words?

Let's say that I have a file containing several occurrences of the word foo and several occurrences of the word bar.

I need to make all the words foo become bar and inversely all the words bar become foo.

What is the most efficient way to do that?

My first thought was to make it 3 steps:

• First make bar become something temporary: %s/bar/barTEMP/g
• Then make foo become bar: :%s/foo/bar/g
• Finally substitute barTEMP: :%s/barTEMP/foo/g

It is an implementation of a classical algorithm to switch the value of two variables but is there a more efficient way to do this?

I know I can write a function to do the 3 substitutions for me but what I'm wondering is if there is a different method than using a temporary substitution. For example I was thinking maybe something could be done by using an | in the search pattern:

:%s/\(foo\|bar\)/???/g

But that would require to make the replacement string change depending on the actually matched word and I don't know how to do that. (Note that this idea is just an example, if someone come up with something better that would be nice too)

• I suppose this is the original source with full commentary on how it works. – Tumbler41 Aug 5 '16 at 13:40
• Tim Pope's abolish provides some syntactic sugar for it: :%S/{foo,bar}/{bar,foo}/g. This works well as long as you don't want to match only whole words. – Sato Katsura Aug 5 '16 at 13:42
• I usually use the ternary operator in a replacement expression for just two words (not very obviously at :h expr1), though using a dictionary is obviously better for >2 words. – Antony Aug 5 '16 at 14:11
• Yeah, it took me several minutes to find it, so, when I finally did, I thought I'd better mention where it was. :-) – Antony Aug 5 '16 at 16:30

Posting this so it can have an answer on our SE, but this is this source with full explanation.

Here's a good way to use a single regex to do multiple substitutions:

:%s/foo\|bar/\={'foo':'bar','bar':'foo'}[submatch(0)]/g

See :help sub-replace-expression and :help Dictionary for Vim's documentation on how this works.

• Thanks for this one, I didn't saw it on SO. That seems like a good way to go. – statox Aug 5 '16 at 15:13
• Just mentioning the solution using the ternary operator that @Antony suggested above: :%s/foo\|bar/\=submatch(0) == "foo" ? "bar" : "foo"/g. – Rich Oct 27 '17 at 9:15

For vanilla vim, Tumbler41's answer is probably the best way to go. If you are OK with installing plugins, you could use tpope/vim-abolish to do this.

This plugin supplies many awesome feature, but the relevant one for this case is called "Subvert" (abbreviated to :%S. Essentially, it allows you to create a list of matches, and a list of replacements. I like the example from the README on the plugin, so I'll use that. If you want to change "child" to "adult", while simultaneously changing "children" to "adults", that is a single subvert command.