t() {
    printf '%s  |  %s\n' "$1" "$2"
  }
  v="'"       # v <- '

  #--
  t "${v/$'\''/$'\''}"        "'"
  t  ${v/$'\''/$'\''}         "'"
  t "${v/$'\''/x}"            "x"
  t  ${v/$'\''/x}             "x"
  t "${v/x/$'\''}"            "'"
  t  ${v/x/$'\''}             "'"
  t "${v/x/$'\x5c\''}"        "'" 
  t  ${v/x/$'\x5c\''}         "'" 
  t "${v/\'/\'}"              "'"
  t  ${v/\'/\'}               "'"
  t  ${v/\'/x}               "x"

echo "'"
echo "$'\''"

echo $'\''

echo $'\'abcd\''
echo "$'\'abcd\''"

v=1
echo ${v/1/\'}
echo ${v/\'/2}