How do I check if a string contains a substring in EK9?

← Common String Operations · Ref: Q171

EK9 uses the contains operator for substring checks and matches for regex pattern matching.

CONTAINS OPERATOR

Check if a string contains a substring:

  if sentence contains "fox"
    stdout.println("Found fox")

Returns Boolean. Case-sensitive.

IS IN / IS NOT IN

Natural language syntax:

  if "fox" is in sentence
    stdout.println("Found")
  if "wolf" is not in sentence
    stdout.println("Not found")

MATCHES (REGEX)

For pattern-based searching:

  if sentence matches /[Ff]ox/
    stdout.println("Matches fox pattern")

See Q37 for string basics. See Q33 for regular expressions.

Example

defines module qa.stringops.contains

  defines program
    StringContainsDemo()
      stdout <- Stdout()

      sentence <- "The Quick Brown Fox Jumps"

      // === CONTAINS OPERATOR ===

      stdout.println(`Contains 'Brown': ${sentence contains "Brown"}`)
      stdout.println(`Contains 'wolf': ${sentence contains "wolf"}`)

      // === IS IN / IS NOT IN ===

      if "Quick" is in sentence
        stdout.println("Found Quick")

      if "wolf" is not in sentence
        stdout.println("wolf not found")

      // === MATCHES (REGEX) ===

      if sentence matches /.*Fox.*/
        stdout.println("Matches Fox pattern")

      if sentence matches /.*[Bb]rown.*/
        stdout.println("Matches Brown pattern (case flexible)")

      // Case-sensitive contains
      stdout.println(`Contains 'quick' (lowercase): ${sentence contains "quick"}`)
      stdout.println(`Contains 'Quick' (correct case): ${sentence contains "Quick"}`)

Common mistakes

E50060 — String has no indexOf() method. Use the contains operator for substring checks. See ek9 -h E50060 for details.

Incorrect:

sentence.indexOf("Brown") >= 0

Correct:

sentence contains "Brown"

Other ways to ask this

How do I search for text within a string in EK9?
What is the EK9 equivalent of string.contains()?
How do I check if a string includes a substring in EK9?

Coming from another language?

Java: str.contains(sub), str.matches(regex). Python: sub in str, re.search(). Rust: str.contains(sub). Go: strings.Contains(str, sub). JavaScript: str.includes(sub), str.match(regex). Kotlin: sub in str, str.contains(sub). EK9: str contains sub, sub is in str, str matches /pattern/.

Keywords: indexOf, match, search, substring, check, includes, find, string, contains, text