How do you append to an indirect parameter expansion of an array in BASH?

Question

I know you can create an indirect parameter expansion to an array like so:

var1=\"target\"
var2=\"arrayname\"
targetarrayname=( \"one\" \"two\" \"three\" )
b         


        

Answer 1

#!/bin/bash

var1="target"
var2="arrayname"
targetarrayname=( "one" "two" "three" )
builtarrayname="${var1}${var2}[@]"
echo ${!builtarrayname} # prints "one two three"

eval "${builtarrayname:0:-3}+=( 'foo' )"

echo ${!builtarrayname} # prints "one two three foo"

Do note though that eval could be considered evil :p You need to be sure that you only have sanitized input to eval statements, to avoid the possibility of unintended code execution.

EDIT:

The :0:-3 in eval "${builtarrayname:0:-3}+=( 'foo' )" removes [@] from the literal string that $builtarrayname contains. Since assignment of arrays only use the variable name, we had to remove it. ( read more here to see how string manipulation in variables work )

and no, I don't think it can be done without eval, as that's how the left side of the assignment gets resolved before the assignment occurs (see this nice answer for more info on eval.