Vim regexp example: make a variable out of params

Today I wrote a regexp to change params[:page] into page. Here you are:

:'<,'>s/params\[:\(\p\{-}\)\]/\1/g

Let’s explain it briefly:

• the first part, :'<,'>s/, is the vim command to substitute a pattern (or a regexp) with another one. The <,'> part tells vim to operate on the visually selected text.

• the second part is the trickiest one. Let’s see it part to part:

• params\[: is the first part of the string we want to match. the \ is used to escape the [ character.

• \(\p\{-}\) is the content between params[: and ]. It consists of a sequence of printable characters (\p). The \( and \) characters around the sequence make it accessible to commands like substitute. I used the \{-} quantifier instead of the \+ because it is the non-greedy version; so, for example, if I had

  params[:page] = [ "a", "b", "c" ]
  

  Then \p\{-} would match only :page, while \p\+ would match :page] = [ "a", "b", "c" .

• the \] part of the second block instructs the regexp parser to stop matching characters when it finds a ] char.

• The third part, \1, tells vim what to replace with: the first match of the previous regexp. So, vim searches for the first \( and reads until \), matches this and uses it for the substitution.

• Finally, g tells vim to make a global change and not to stop after the first occurrence.