Here, in this tutorial we will see some of the array manipulation commands in MEL that can be put to use while creating your own scripts.
Problem:
Getting a List of objects that are of a particular type, based on user input.
Solution:

ak_listObjectsOfType(“$type”)

where $type can be mesh, nurbsCurve, ikHandle, joint, multiplyDivide….

 global proc ak_listObjectsOfType(string $type)
 {
 string $transformList[],$cleanList[],$conflictList[];
 string $newName,$each;
 $choiceList = `ls -type $type`;
 if ($type == "nurbsCurve" || $type == "mesh")
 {
 $transformList = `listRelatives -parent $choiceList`;
 }
 else
 {
 $transformList = $choiceList;
 }
 int $i = 0;
 for ($each in $transformList)
 {
 if (stringArrayContains($each,$cleanList)!=1)
 {
 stringArrayInsertAtIndex($i,$cleanList,$each);
 $i++;
 }
 }
 print $cleanList;
 }
 

Commands:
ls, listRelatives, stringArrayContains, stringArrayInsertAtIndex
Discussion:
The result can be easily achieved using the command ls. Using the -type flag followed by the object type will give a list of objects of that specific type.
For eg: ls -type “ikHandle” will return a list of all ik handles in the scene
But specifying mesh or nurbsCurve will give the shape names instead of the transform names. By running a listRelatives -parent on the returning list will give the transform nodes, but this will include duplicate entries if the mesh is having a deformer attached to it since ls -type “mesh” return a list of all the intermediate objects too. So we will be using the script listed above to print out objects that matches the user entry type.

The pseudocode for the script is as follows.

global procedure ak_listObjectsOfType($type of type string )
 {
 declare String Arrays $transformLis,$cleanList and $conflictList
 declare String $newName and $each;
 store the value of ls command of node type $type in $choiceList
 if ($type  is "nurbsCurve" or   "mesh")
 {
 store the parents of $choiceList in $transformList;
 }
 else
 {
 Assign  the value of $choiceList itself to $transformList
 }
 initialize index number $i  to zero;
 for (each element  in $transformList)
 {
 if (string Array $cleanList doesn't contain $each)
 {
 insert $each at position $i of $cleanList
 increment the index value $i by 1
 }
 }
 print the $cleanList
 }

The command stringArrayContains() checks a string exists in a string Array or not and returns true of false. stringArrayInsertAtIndex() will insert a string in to the index position position in the string Array. Both the command names are self-explanatory.