Increment number in string using StringReplace?

Questions
1

(* how to transform “abc2” into “abc3” ? *)

string = "abc2";

regex = ".$";

newString = 
 StringReplace[string, 
  RegularExpression[regex] -> IntegerString[1+$0 ]]

(* output expected: “abc3” - but output is:

"abc"~~IntegerString[1+$0]

*)

2

In[1]:= string = “abc2”;

In[2]:= StringJoin[StringDrop[string, {4}], 
 ToString[(ToExpression@StringPart[string, 4] + 1)]]

Out[2]= "abc3"
3

(* solved:

:> not → ,the latter,Rule,is evaluated immediately *)

string = “abc2”;

regex = “.$”;

newString =
StringReplace[string,
RegularExpression[regex] :> ToString[1 + FromDigits[“$0”]]]

(* output is:
“abc3”
*)