[%CFEngine_function_prototype(mode, options, expression)%]

Description: Returns expression evaluated according to mode and options. Currently only the math mode with infix option is supported for evaluating traditional math expressions.

All the math is done with the C double type internally. The results are returned as a string

The supported infix mathematical syntax, in order of precedence, is:

• ( and ) parentheses for grouping expressions
• ^ operator for exponentiation
• * and / operators for multiplication and division
• % operators for modulo operation
• + and - operators for addition and subtraction
• == “close enough” operator to tell if two expressions evaluate to the same number, with a tiny margin to tolerate floating point errors. It returns 1 or 0.

The numbers can be in any format acceptable to the C scanf function with the %lf format specifier, followed by the k, m, g, t, or p SI units. So e.g. -100 and 2.34m are valid numbers.

In addition, the following constants are recognized:

• e: 2.7182818284590452354
• log2e: 1.4426950408889634074
• log10e: 0.43429448190325182765
• ln2: 0.69314718055994530942
• ln10: 2.30258509299404568402
• pi: 3.14159265358979323846
• pi_2: 1.57079632679489661923 (pi over 2)
• pi_4: 0.78539816339744830962 (pi over 4)
• 1_pi: 0.31830988618379067154 (1 over pi)
• 2_pi: 0.63661977236758134308 (2 over pi)
• 2_sqrtpi: 1.12837916709551257390 (2 over square root of pi)
• sqrt2: 1.41421356237309504880 (square root of 2)
• sqrt1_2: 0.70710678118654752440 (square root of 1/2)

The following functions can be used, with parentheses:

• ceil and floor: the next highest or the previous highest integer
• log10, log2, log
• sqrt
• sin, cos, tan, asin, acos, atan
• abs: absolute value
• step: 0 if the argument is negative, 1 otherwise

[%CFEngine_function_attributes(mode, options, expression)%]

Example:

[%CFEngine_include_snippet(eval.cf, #+begin_src cfengine3, .*end_src)%]

Output:

2013-09-14T08:34:16-0400 info: eval error: expression could not be parsed (input 'x') 2013-09-14T08:34:16-0400 info: eval error: expression could not be parsed (input '+ 200') 2013-09-14T08:34:16-0400 info: eval error: expression could not be parsed (input '- - -') 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('x') = '' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('+ 200') = '' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('floor(3.4)') = '3.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('sqrt(0.2)') = '0.447214' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('2 + 3 - 1') = '4.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('sin(20)') = '0.912945' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('200 - 100') = '100.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('20 % 3') = '2.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('ceil(3.5)') = '4.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('200 + 100') = '300.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('pi') = '3.141593' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('- - -') = '' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('-3.400000 == -3.400001') = '0.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('3 / 0') = 'inf' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('e') = '2.718282' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('cos(20)') = '0.408082' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('') = '0.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('-1^2.1') = '-nan' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('abs(-3.4)') = '3.400000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('-3.4 == -3.4') = '1.000000' 2013-09-14T08:34:16-0400 notice: R: math/prefix eval('3^3') = '27.000000'