Numeric Built-in Functions

Here is a full list of built-in functions that work with numbers. Optional parameters are enclosed in square brackets ("[" and "]").

int(x)

This produces the nearest integer to x, located between x and zero, truncated toward zero. For example, int(3) is three, int(3.9) is three, int(-3.9) is -3, and int(-3) is -3 as well.

sqrt(x)

This gives you the positive square root of x. It reports an error if x is negative. Thus, sqrt(4) is two.

exp(x)

This gives you the exponential of x (e ^ x), or reports an error if x is out of range. The range of values x can have depends on your machine's floating point representation.

log(x)

This gives you the natural logarithm of x, if x is positive; otherwise, it reports an error.

sin(x)

This gives you the sine of x, with x in radians.

cos(x)

This gives you the cosine of x, with x in radians.

atan2(y, x)

This gives you the arctangent of y / x in radians.

rand()

This gives you a random number. The values of rand are uniformly-distributed between zero and one. The value is never zero and never one. Often you want random integers instead. Here is a user-defined function you can use to obtain a random non-negative integer less than n:

function randint(n) {
     return int(n * rand())
}

The multiplication produces a random real number greater than zero and less than n. We then make it an integer (using int) between zero and n - 1, inclusive. Here is an example where a similar function is used to produce random integers between one and n. This program prints a new random number for each input record.

awk '
# Function to roll a simulated die.
function roll(n) { return 1 + int(rand() * n) }

# Roll 3 six-sided dice and
# print total number of points.
{
      printf("%d points\n",
             roll(6)+roll(6)+roll(6))
}'

Caution: In most awk implementations, including gawk, rand starts generating numbers from the same starting number, or seed, each time you run awk. Thus, a program will generate the same results each time you run it. The numbers are random within one awk run, but predictable from run to run. This is convenient for debugging, but if you want a program to do different things each time it is used, you must change the seed to a value that will be different in each run. To do this, use srand.

srand([x])

The function srand sets the starting point, or seed, for generating random numbers to the value x. Each seed value leads to a particular sequence of random numbers.(10) Thus, if you set the seed to the same value a second time, you will get the same sequence of random numbers again. If you omit the argument x, as in srand(), then the current date and time of day are used for a seed. This is the way to get random numbers that are truly unpredictable. The return value of srand is the previous seed. This makes it easy to keep track of the seeds for use in consistently reproducing sequences of random numbers.

Go to the first, previous, next, last section, table of contents.