Find: regex replace

The find bar's replace row can use a regular expression, whose parenthesised groups the replacement can reorder with $1, $2 and so on. doubled() computes price * 2 - this lesson rewrites it to 2 * price. To play it in the IDE: Help > Lessons > Finding…, or ek9 -ide -lesson find-regex-replace.

Start from

The code the lesson starts from: copy it into a file of your own and follow the steps.

shop.ek9

#!ek9
defines module lesson.finding.shop

  defines class

    Total
      total as Integer: 0

      addItem()
        -> price as Integer
        //total grows by one item's price
        total += price

      subtotal() as pure
        <- rtn as Integer: total

      default operator ?

  defines function

    priceLabel() as pure
      -> price as Integer
      <- rtn as String: `Total: ${price}`

    doubled() as pure
      -> price as Integer
      <- rtn as Integer: price * 2

  defines program

    ShowTotal()
      stdout <- Stdout()
      total <- Total()
      total.addItem(5)
      total.addItem(10)
      stdout.println(priceLabel(total.subtotal()))
      stdout.println("The running total is shown above")

//EOF

receipt.ek9

#!ek9
defines module lesson.finding.shop

  defines function

    receiptFooter() as pure
      -> grandTotal as Integer
      <- rtn as String: `Grand total: ${grandTotal}`

  defines program

    ShowReceipt()
      stdout <- Stdout()
      total <- Total()
      total.addItem(20)
      stdout.println(receiptFooter(total.subtotal()))

//EOF

till.ek9

#!ek9
defines module lesson.finding.till

  defines program

    ShowTill()
      stdout <- Stdout()
      total <- 0
      total += 15
      stdout.println(`Till total: ${total}`)

//EOF

Step 1: Open Replace

Choose Edit > Replace…

Step 2: A regular expression

Turn on the regular expression toggle (.*), then type (\w+) * (\d) into the field - a word, then * , then a digit, each side held in its own group. One match.

$The EK9 IDE once this is done: Turn on the regular expression toggle (.*), then type (\w+) * (\d) into the field - a word, then * , then a digit, each side held in its own group$

Step 3: Replace with a capture group

Type $2 * $1 into the Replace field - the digit first, then the word: the two groups swapped. Choose Replace All.

Text mode changes this file's buffer, not yet saved. Choose File > Save.

The result

That is a regular expression's capture groups used in the replacement: price * 2 read, and reordered into 2 * price. Replace changes only the current match; Replace All - just used - changes every match in the file. Text mode edits the buffer, so the file is saved before it is really changed.