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

Note that this won't work

foo=HELLO
bar=WORLD
foobar=PREFIX_$foo_$bar

as it seems to drop $foo and leaves you with:

PREFIX_WORLD

but this will work:

foobar=PREFIX_"$foo"_"$bar"

and leave you with the correct output:

PREFIX_HELLO_WORLD