bash - How do you append to an already existing string?

Question

I want append to a string so that every time I loop over it will add say "test" to the string.

Like in PHP you would do:

$teststr = "test1
"
$teststr .= "test2
"
echo = "$teststr"

echos:

test1
test2

But I need to do this in a shell script

Answer 1

In classic sh, you have to do something like:

s=test1
s="${s}test2"

(there are lots of variations on that theme, like s="$s""test2")

In bash, you can use +=:

s=test1
s+=test2