Many people are unaware that string concatenation using the += syntax is fully supported in modern versions of both the Bash and Korn shells
Here is a simple example which demonstrates the syntax:
str="Hello" $ str+=" " $ str+="World" $ echo $str Hello World $
If you use this syntax with “numbers”, you end up with a string that looks like a number but is not a number.
$ a=2 $ a+=4 $ echo $a $ 24