Append to variable with "read" command

Question

With Bash, you can append to a variable, example

$ foo=Hello

$ foo+=world

$ echo $foo
Helloworld

However, is this possible with the read command? Something like

$ foo=Hello

$ read --append foo
world

$ echo $foo
Helloworld

Answer 1

Not directly, so use a temp variable.

foo="Hello"
read tmp
foo+="$tmp"

Answer 2

You can fake it, kind of, using readline:

$ foo=Hello
$ read -e -i"$foo" foo
Hello

When using readline via the -e flag, the argument to -i is put on the first line of the input to get you started. You're not so much appending to foo as giving foo a whole new value, which just happens to begin with the old value if you don't edit the initial line.