#!/usr/bin/env bash

# This script replaces a section of text in a file marked by the bash
# regular expression passed as the first argument and ending with the
# second argument with the text in the the third argument The beginning
# and ending lines themselves are discarded when replaced.

ssection () {
  local beg="$1" end="$2" buf="$3"

  [[ -z "$beg" || -z "$end" ]] && echo "usage: ${0##*/} BEGX ENDX [STRING]" && return 1

  local in=no

  while IFS= read -r line; do


    if [[ "$line" =~ $beg ]]; then
      in=yes
      continue
    fi

    if [[ "$line" =~ $end ]]; then
      in=no
      printf "$buf\n\n"
      continue
    fi

    [[ "$in" == no ]] && echo "$line"

  done

}

ssection "$@"