doh is a simple command-line tool for conversion between different numeral systems.
$ doh 123
IN: dec: 123
hex: 7B
dec: 123
oct: 173
$ doh 0xABC
IN: hex: 0xABC
hex: ABC
dec: 2748
oct: 5274
$ doh 0644
IN: oct: 0644
hex: 1A4
dec: 420
oct: 644
$ doh duh
Not a number.