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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?

John
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  • 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 Mar 18 '19 at 07:36
  • So as Gordon said, the second will not work: `echo "${!alias[foo]}" "${!alias[hello]}"` will output `bar bar`. The `world` is lost. – KamilCuk Mar 18 '19 at 07:41

1 Answers1

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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
Inian
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