s1 = "abcd"
s2 = "adab"
s3 = "ab"

String.starts_with?(s1, s3)
# => true
String.starts_with?(s2, s3)
# => false

String.ends_with?(s1, s3)
# => false
String.ends_with?(s2, s3)
# => true

String.contains?(s1, s3)
# => true
String.contains?(s2, s3)
# => true