Access bash associate array via variable indirection

Question

I wish to access an associative array using a variable. The example in the accepted answer to this post is exactly what I want:

$ declare -A FIRST=( [hello]=world [foo]=bar )
$ alias=FIRST
$ echo "${!alias[foo]}"

however this does not work for me when using bash 4.3.48 or bash 3.2.57. It does however work if I don't declare ("declare -A") the array i.e. this works:

$ FIRST[hello]=world 
$ FIRST[foo]=bar
$ alias=FIRST
$ echo "${!alias[foo]}"

Is there any problem with not declaring the array?

There's a huge problem: it creates a numerically-indexed array, rather than an associative (string-indexed) array. Since hello and foo aren't defined, FIRST[hello] and FIRST[foo] are both equivalent to FIRST[0]. — Gordon Davisson
– Gordon Davisson, Commented Mar 18, 2019 at 7:36
So as Gordon said, the second will not work: echo "${!alias[foo]}" "${!alias[hello]}" will output bar bar. The world is lost. — KamilCuk
– KamilCuk, Commented Mar 18, 2019 at 7:41

Inian · Accepted Answer · 2019-03-18 07:46:57Z

It works just as expected, you just missed out defining one more level of indirection to access the value,

declare -A first=()
first[hello]=world 
first[foo]=bar
alias=first
echo "${!alias[foo]}"

The above result would obviously be empty as the other answer points out as there is no reference created yet to the array key. Now define an item to introduce a second level of indirect reference to point out to the actual key value.

item=${alias}[foo]
echo "${!item}"
foo

Now point item to the next key hello

item=${alias}[hello]
echo "${!item}"
world

Or a more detailed example would be, to run a loop over the keys of the associative array

# Loop over the keys of the array, 'item' would contain 'hello', 'foo'
for item in "${!first[@]}"; do    
    # Create a second-level indirect reference to point to the key value
    # "$item" contains the key name 
    iref=${alias}["$item"]
    # Access the value from the reference created
    echo "${!iref}"
done

Collectives™ on Stack Overflow

Access bash associate array via variable indirection

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related