Is it possible to make a substitution command that preserves the case of the matched pattern?

Question

Consider the following constant definition:

define("_TBL_USERS","users");

Now, I want to transform it into:

define("_TBL_USER_ITEMS","user_items");

I tried the command:

s/\(user\)s\?/\1_items/gi

And the result is:

define("_TBL_USER_items","user_items");

Is there a way to use a substitute command that will modify the case depending on the matched pattern, so the first items is substituted in uppercase?

Answer 1

There is plugin for this - Abolish by Tim Pope. No configuration required.

For your example do one of these commands (does not matter which):

:Subvert;USERS;USER_ITEMS;g

:Subvert;users;user_items;g

Answer 2

It's possible to do this with one substitution command but it's a bit hairy and you might want to just use two substitutions. For instance here's a two substitution version that has a bit of a shortcut in it...

:s/\(user\)s\?/\1_items/gI | s/\(USER\)S\?/\U~/g

The ~ in the replacement part of the second command copies the replacement of the last executed substitution (in our case from the LHS of the |). By prepending that with \U we force \1_items to uppercase.

If you want to know the single substitution version...better take a seat. ;)

:s/\(user\)s\?/\=submatch(1) . (submatch(1) ==# 'user' ? '_items' : '_ITEMS')/gi

This is using what's known as a sub-replace expression. I've answered a couple question recently using this technique: How to run a substitute command on only a certain part of the line and How to create regex group with dependency with earlier group via math operations

The key is the \= that begins the substitution. It means "everything after this point is to be evaluated as a VimL expression and the result of that evaluation becomes the replacement string". submatch(1) is equivalent to \1 and we're appending to that a string that is conditional on the value of submatch(1). Specifically, the part between the parens says, If the submatch is case sensitively equal to 'user' then append to the submatch "_items" otherwise append "_ITEMS". "

The two-substitution version is easier to understand and less typing so that's what I would use. If you really want to avoid typing a pattern more than once then, hmmm, you could use this, I suppose...

:let c='s/\(USER\)S\?/\1_ITEMS/I' | exe c | exe tolower(c).'I'

Alternatively, run the first substitution then run a second command...

:s/\(USER\)S\?/\1_ITEMS/I
:exe tolower(@:).'I'

Both of these do two substitutions but at least you only have to type one of them. ;)

(Just in case there's confusion, I don't actually recommend using either of the last two...they're a bit too hacky. But, hey, if you want to do so anyways then go for it. :)