DB<131> $str=$str0
 => " bla0 \"ignore a1\" bla1 \"ignore a2\" bla2"

  DB<132> $x=0;$extract[$x++]=$& while $str =~ s/"[^"]*"/<$x>/
 => ""

  DB<133> @extract 
 => ("\"ignore a1\"", "\"ignore a2\"")

  DB<134> $str =~ s/a/A/g
 => 3

  DB<135> $str
 => " blA0 <0> blA1 <1> blA2"

  DB<136> $str =~ s/<(\d+)>/$extract[$1]/g
 => 2

  DB<137> $str
 => " blA0 \"ignore a1\" blA1 \"ignore a2\" blA2"