R function to that replaces 'key' tagged words (eg. $word) within a string with the value contained in the system by the local variable 'word'

SubSV

SubSV <- function(string, env, key = '$'){
  # Replaces 'key' tagged words (eg. $word) within a string with the value
  # contained in the system by the local variable 'word'
  #
  # Args:
  #   string: string with 'key' tagged words.
  # Returns:
  #   string with every 'key' tagged word replaced.
  # Example:
  #   this <- 'by that'; SubSV('replace $this', environment())

  while(grepl(paste('\\',key,sep=''),string)){
    par <- gsub(paste('\\',key,sep=''),'',
                regmatches(string,
                           regexpr(paste('\\',key,'\\w*',sep=''),string)))
    regmatches(string,
               regexpr(paste('\\',key,'\\w*',sep=''),
                       string)) <- get(par, envir = env)
  }
  return(string)
}