eval

Example 1

eval("select -cl")

Executes the command select -cl, which deselects all objects in the scene. Though the return value is not used in this example, it contains the command output.

Example 2

string $cmd = "select -cl";
eval($cmd);

The first statement assigns the command string select -cl to the string variable $cmd. The second statement executes the contents of $cmd, which is the command select -cl.

Example 3

string $mycommand = "sphere";
eval($mycommand+"-r 5");

The first statement assigns the string sphere to the variable $mycommand. The second statement appends -r 5 to the string sphere and executes the complete command sphere -r 5. This creates a sphere with a radius of 5 grid units.

Example 4

string $a[];
$a = eval("ls -lights");
print($a);

The first statement defines an array of strings named $a. The second statement executes the MEL command ls -lights, then assigns the command’s output to array $a. The third statement displays the contents of $a to the Script Editor as follows:

ambientLightShape1
directionalLightShape1

Each line of command output appears on a new line. Each command output line is an array element. Maya formats array output with each array element on a new line.

Example 5

Suppose you’ve created a MEL script file named bunk.mel in your Maya scripts directory and it contains this procedure:

global proc string bunk()
{
string $fog;
if (rand(2) < 1)
	$fog = "particle";
else
	$fog = "sphere";
return $fog;
}

Further suppose you create this expression:

string $name = bunk();
eval($name);
print($name);

The first expression statement executes the bunk() procedure in the bunk.mel script file. In the bunk procedure, the if-else statement generates a random floating point value between 0 and 2, then compares its value to 1.

If the value is less than 1, the statement assigns the MEL command string particle to $fog. If the value is greater than 1, $fog receives the command string sphere.

The procedure finishes executing and passes the value of $fog back to the calling procedure, bunk() in the expression. This assigns the command string to the variable $name.

The eval function executes the command string stored in the $name. For example, the statement might execute particle, which creates a particle at the origin of the workspace.

The fourth statement displays the contents of $name, for example, particle.

The expression executes each frame and creates a new particle or sphere.