"Basically I am trying to merge abc_1, abc_2 and abc_3 into abc_1 and than delete abc_2 and abc_3. Not sure how am I suppose to call them in the while loop"
Basically what you are writing is slow, buggy, complex code. Making this easy would encourage people to use it, which would make their code slow, buggy, insecure, pointlessly complex, and harder to debug. Deciding to use numbered variables is how some beginners force themselves into writing slow code. But you don't have to do this.
Your best solution is to avoid this situation entirely: do not magically access variable names using slow introspective methods (e.g. who, etc). There is no reason why you should have numbered variables in your workspace: whether loading the data from file or generating it in a loop it is trivial to put all of that data into one array using indexing. Indexing is simple, neat, easy to debug, and very very efficient (unlike what you are trying to do). Read the links at the bottom of this post to see examples of how to avoid this situation.
You would do well to consult the relevant parts of the documentation: "A frequent use of the eval function is to create sets of variables such as A1, A2, ..., An, but this approach does not use the array processing power of MATLAB and is not recommended. The preferred method is to store related data in a single array"
Note that accessing is just as slow as creating those variables, for the reasons discussed in the documentation, the blogs, and this forum. You might as well read some of the discussions on this topic:
https://www.mathworks.com/matlabcentral/answers/143-how-do-i-make-a-series-of-variables-a1-a2-a3-a10
or any of the other countless times that this has been discussed before.
