In awk, all numbers are in decimal (i.e., base 10). Many other
programming languages allow you to specify numbers in other bases, often
octal (base 8) and hexadecimal (base 16).
In octal, the numbers go 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, and so on.
Just as ‘11’ in decimal is 1 times 10 plus 1, so
‘11’ in octal is 1 times 8 plus 1. This equals 9 in decimal.
In hexadecimal, there are 16 digits. Because the everyday decimal
number system only has ten digits (‘0’–‘9’), the letters
‘a’ through ‘f’ represent the rest.
(Case in the letters is usually irrelevant; hexadecimal ‘a’ and ‘A’
have the same value.)
Thus, ‘11’ in
hexadecimal is 1 times 16 plus 1, which equals 17 in decimal.
Just by looking at plain ‘11’, you can’t tell what base it’s in. So, in C, C++, and other languages derived from C, there is a special notation to signify the base. Octal numbers start with a leading ‘0’, and hexadecimal numbers start with a leading ‘0x’ or ‘0X’:
11Decimal value 11
011Octal 11, decimal value 9
0x11Hexadecimal 11, decimal value 17
This example shows the difference:
$ gawk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }'
-| 9, 11, 17
Being able to use octal and hexadecimal constants in your programs is most useful when working with data that cannot be represented conveniently as characters or as regular numbers, such as binary data of various sorts.
gawk allows the use of octal and hexadecimal
constants in your program text. However, such numbers in the input data
are not treated differently; doing so by default would break old
programs.
(If you really need to do this, use the --non-decimal-data
command-line option;
see Allowing Nondecimal Input Data.)
If you have octal or hexadecimal data,
you can use the strtonum() function
(see String-Manipulation Functions)
to convert the data into a number.
Most of the time, you will want to use octal or hexadecimal constants
when working with the built-in bit-manipulation functions;
see Bit-Manipulation Functions
for more information.
Unlike in some early C implementations, ‘8’ and ‘9’ are not
valid in octal constants. For example, gawk treats ‘018’
as decimal 18:
$ gawk 'BEGIN { print "021 is", 021 ; print 018 }'
-| 021 is 17
-| 18
Octal and hexadecimal source code constants are a gawk extension.
If gawk is in compatibility mode
(see Command-Line Options),
they are not available.
| A Constant’s Base Does Not Affect Its Value |
|---|
|
Once a numeric constant has
been converted internally into a number,
$ gawk 'BEGIN { printf "0x11 is <%s>\n", 0x11 }'
-| 0x11 is <17>
|