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\n"
$teststr .= "test2\n"
echo = "$teststr"

echos:

test1
test2

But I need to do this in a shell script

Answer 1

teststr=$'test1\n'
teststr+=$'test2\n'
echo "$teststr"

Answer 2

$ string="test"
$ string="${string}test2"
$ echo $string
testtest2

Answer 3

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

Answer 4

#!/bin/bash
message="some text"
message="$message add some more"

echo $message

some text add some more