regex - Replace nested expressions using Ruby -

how replace x between bracket in expression below:

{ x} x {x } x x {} x{x}{  x} 

without preserving spaces inside braces

you can use .gsub both look-behind , look-ahead operator:

# replace instances of x within curly braces y '{ x} x {x } x x {} x{x}{  x}'.gsub(/(?<={)\s*x\s*(?=})/, 'y') 

output:

"{y} x {y} x x {} x{y}{y}" 

preserving spaces inside braces

you need alternate approach preserving spaces:

'{ x} x {x } x x {} x{x}{  x}'.gsub(/{(\s*)x(\s*)}/, '{\1y\2}') 

output:

"{ y} x {y } x x {} x{y}{  y}"