How do I pad a string to a fixed width in EK9?

← Common String Operations · Ref: Q176

EK9 strings have .leftPadded(n) and .rightPadded(n) methods for padding to a fixed width.

RIGHT PADDED

Pad with spaces on the right to reach width n:

  padded <- myString.rightPadded(20)

Useful for left-aligned columns. If the string is already longer than n, it is returned unchanged.

LEFT PADDED

Pad with spaces on the left to reach width n:

  padded <- myString.leftPadded(20)

Useful for right-aligned columns.

FORMATTING COLUMNS

Combine padding for tabular output:

  stdout.println(`${name.rightPadded(15)} ${score.leftPadded(5)}`)

See Q37 for comprehensive string operations. See Q173 for trim (the complement of padding).

Example

defines module qa.stringops.padding

  defines program
    StringPaddingDemo()
      stdout <- Stdout()

      // === RIGHT PADDED (left-aligned) ===

      word <- "Hello"
      rightPad <- word.rightPadded(20)
      stdout.println(`Right padded: [${rightPad}]`)

      // === LEFT PADDED (right-aligned) ===

      leftPad <- word.leftPadded(20)
      stdout.println(`Left padded: [${leftPad}]`)

      // === FORMATTING COLUMNS ===

      names <- ["Alice", "Bob", "Charlie"]
      amounts <- ["1234", "56", "789"]

      idx <- 0
      for name in names
        amount <- amounts.getOrDefault(idx, "0")
        stdout.println(`${name.rightPadded(12)} ${amount.leftPadded(8)}`)
        idx := idx + 1

      // === STRING LONGER THAN WIDTH ===

      longStr <- "A very long string"
      padded <- longStr.rightPadded(5)
      stdout.println(`Long string padded to 5: [${padded}]`)

Common mistakes

E50060 — String has no padEnd() method. The correct method names in EK9 are rightPadded() and leftPadded(). See ek9 -h E50060 for details.

Incorrect:

rightPad <- word.padEnd(20)

Correct:

rightPad <- word.rightPadded(20)

E11068 — Concatenating 3 or more string parts with + triggers E11068. Use backtick interpolation instead. See ek9 -h E11068 for details.

Incorrect:

stdout.println(name.rightPadded(12) + " " + amount.leftPadded(8))

Correct:

stdout.println(`${name.rightPadded(12)} ${amount.leftPadded(8)}`)

Coming from another language?

Java: String.format("%-20s", str) for left-align, String.format("%20s", str) for right-align. Python: str.ljust(20), str.rjust(20). Rust: format!("{:<20}", str), format!("{:>20}", str). Go: fmt.Sprintf("%-20s", str). JavaScript: str.padEnd(20), str.padStart(20). Kotlin: str.padEnd(20), str.padStart(20). EK9: str.rightPadded(20), str.leftPadded(20).

Keywords: right, string, fixed, text, align, width, column, left, pad, format, padding