What is the most efficient way to invert two words?

Question

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?

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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?

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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)

Answer 1

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.

Answer 2

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.

:%S/child{,ren}/adult{,s}/

In your case, you could do

:%S/{foo,bar}/{bar,foo}

One important note about this approach is that it doesn't support regexes very well, and it defaults to case-sensitive, so it would also change "FOO" to "BAR". However, for simple substitutions, this approach is very simple and convenient.