if str.index( "abc" ) != nil then
# 処理
end
num = 3
str1 = sprintf( "%02d", num )
str2 = "%02d" % num
(Ruby >= 2.2)
if str.unicode_normalized?
# OK
else
# NG
end
begin
str.encode('ISO-2022-JP', invalid: nil)
# OK
rescue Encoding::InvalidByteSequenceError, Encoding::UndefinedConversionError => e
# NG
end