Some programming languages usually start with the number 0, indicating that the number is octal. Octal numbers and binary numbers can correspond bit by bit (one bit in octal corresponds to three bits in binary), so they are often used in computer languages.
Octal notation (radix 8) is very common in computer systems, so we can sometimes see people using octal notation. Since one number in hexadecimal can correspond to four binary numbers, it is more convenient to represent binary numbers in hexadecimal. Therefore, octal application is not as good as hexadecimal. Some programming languages provide the ability to use octal symbols to represent numbers, but there are still some older Unix applications that use octal symbols.