How to concatenate string variables in Bash

Question

In PHP, strings are concatenated together as follows:

$foo = \"Hello\";
$foo .= \" World\";

Here, $foo becomes \"Hello World\"

Answer 1

Here is the one through AWK:

$ foo="Hello"
$ foo=$(awk -v var=$foo 'BEGIN{print var" World"}')
$ echo $foo
Hello World