If you seldom use Ruby percent (%) notation in daily work, here’s a quick summary of what I picked up recently.

Delimiter allows any non-alphanum

You can use any non alpha-numeric character as delimiter:

%(any alpha-numeric)
%[char can be]
%%used as%
%!delimiter\!! # escape '!' literal

Bracket pairs no need to escape

No need to escape bracket pairs, even when nested. You can escape, but will need to escape both open and close bracket.

%( (pa(re(nt)he)sis) ) #=> "(pa(re(nt)he)sis)"
%[ [square bracket] ]  #=> "[square bracket]"
%{ {curly bracket} }   #=> "{curly bracket}"
%< <pointy bracket> >  #=> "<pointy bracket>"
%< \<this works as well\> >  #=> "<this works as well>"

Modifiers for String, Regex, Array, Symbol, Shell command

We often use % notation to create String and Array literals. But it also supports Symbol, Regex and shell command.

%(interpolated string (#{ "default" }))
  #=> "interpolated string (default)"
%Q(interpolated string (#{ "default" }))
  #=> "interpolated string (default)"
%q(non-interpolated string)
  #=> "non-interpolated string"
%r(#{ "interpolated" } regexp)i
  #=> /interpolated regexp/i
%w(non-interpolated\ string  separated\ by\ whitespaces)
  #=> ['non-interpolated string', 'separated by whitespaces']
%W(interpolated\ string #{ "separated by whitespaces" })
  #=> ['interpolated string', 'separated by whitespaces']
%s(non-interpolated symbol)
  #=> :'non-interpolated symbol'
%x(echo #{ "interpolated shell command" })
  #=> "interpolated shell command\n"

Here’s some % notation examples written in minitest in case you interested.