August 2011
Beginner to intermediate
600 pages
14h 29m
English
Chapter 19
Numbers
Numbers are central to computing, but this chapter covers some of the problems that can be encountered when dealing with numbers in shell scripts. The first recipe looks at three different methods for listing the numbers in the Fibonacci Sequence. This uncovers some of the limitations on the size of numbers that the shell can deal with, and ways to work around them.
The second recipe deals with conversion of numbers between different bases. Although we normally express numbers in base 10 (the decimal system), base 2 (binary) is the native format used by the CPU. Base 16 (hexadecimal) is very commonly used because it is more compact than base 2, and one byte is neatly displayed in two hexadecimal characters. The netboot.sh recipe uses printf to convert between decimal and hexadecimal; the bc tool can convert numbers from any base to any other, but printf provides the easiest way to represent decimal numbers in both hexadecimal and octal.