Mathematical Calculations & Expression Evaluation:
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  Gui4Cli will evaluate a mathematical expression, if enclosed in 
  brackets with a $ (dollar sign) in front.

  x = $(4*2)     ; will set x to 8

  This can be used anywhere, just as if it were a variable :

  Say 'The result is $(45/(2*4.56))n'

  Gui4Cli will read brackets as if they were quotes - i.e. you
  can have spaces inside the brackets without having to quote 
  the whole thing :

  x = $( 4 * 2 )

  You can also have variables in the brackets, but..
  BECAREFULL : Gui4Cli allows almost any character to be a part
  of a variable name. (This is done because file names - which can
  have almost any character in them - can also be variables (env:)
  or part of the specification of variables (GuiName/VarName))

  So Gui4Cli will also consider things such as +, *, -, / etc to 
  be included in the variable name if there is no space between 
  the end of the name and the operator :

  x = $($var*3)      ; <- wrong

  is wrong, because Gui4Cli will try to find variable "var*3"
  Gui4Cli will understand the end of a variable name if it is
  followed by a space, or a bracket or a '', so

  x = $($var *3)     ; is correct
  x = $(3*$var)      ; is correct
  x = $($var*3)     ; is correct

  The available operators are :

  + - * /    as you know..
  ^          means to the power of = 4^2 = 16

  Note that to get a square root you can do : 

  x = $(25^(1/2))   ; 25 to the half = 5

  Inside the brackets, you can also use the following math
  functions :

  abs(x)     absolute value of x
  sin(x)     sin of x
  cos(x)     cosine of x
  tan(x)     tagent of x
  log(x)     logarithm of x
  ln(x)      natural log of x
  exp(x)     exp of x
  pi         = 3.141592654
  
  example :

  x = $($MyVariable * pi + tan(0.85)-(4*sin(45)))

  I used to know all this stuff, now I can't remember a thing..
  The parser which does the actual calculation was written by 
  Kittiphan Techakittiroj, who put it in the public domain where 
  from I appropriated it with his blessings and put it to good use.

  Here's a calculator :  Run Gui   Source