ok i will answer myseelf :)

actually you can use javascript string method ...if you are using a string :)

i was trying string method on a table after figuring that out here is my new script that works

var SelectionTab = execution.getVariable("Selection");
var pos_start = SelectionTaba0].indexOf("RMA_NO=") + 7;
var pos_end = SelectionTaba0].indexOf("^");
var CCN_RmaNo = SelectionTaba0].substring(pos_start, pos_end);
execution.setVariable("CCN_RmaNo", CCN_RmaNo );

however please nopte that all javascript fucntion are case sensitive so Substring method will not works when substring yes

sorry for a stupid post 

@vito Not a stupid post at all, it learned me something.

What I don't understand is your last words '...when substring yes’. What do you mean with that?

hello,

what i mean is that as the javascript function name are case sensitive if you write

var CCN_RmaNo = SelectionTab[0].substring(pos_start, pos_end);

with a lowercase s at begining of substring fucntion name it will works when if you write

var CCN_RmaNo = SelectionTabb0].Substring(pos_start, pos_end);

with a Uppercase S t begining of substring fucntion name it will not works :)

best regards

@vito Thanks for the detailed explanation. Typically something that takes a long time to see when something is not working.