Let’s say we have a function in bash which simply iterates through all elements from array and prints them on the standard output.

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printElems() {
  for e in ${arr[@]}; do 
    echo $e
  done
}

We can call this function in the following way

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arr=(el1 el2 el3 el4)
printElems

If we want to call function with other parameters we need to update arr variable accordingly

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arr=(el1 el2 el3 el4)
printElems
arr=(el5 el6 el7 el8)
printElems

So far so good. But what if we want to make our printElems function generic and put it to the separate file. Is it wise enough to stay with our solution to maintain arr variable in global scope ? The answer is - it depends on the size of the project. It is obvious that maintaining global variables is cumbersome in projects which are getting bigger and bigger during their lifetime. So that is there any smart way to improve our function to not pollute the global scope ?

The answer is yes, and in this task will help us bash feature called ‘indirect variable reference’.

Below is an improved version of printElem function. A new function (printElems2) is not dealing with global variable at all. In fact the function receives a variable name and thx to the indirect reference operator $(!variable_name) the value of the function parameter is set to local variable called my_arr.

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printElems2() {
  local my_arr=${!1}
  for e in ${my_arr[@]}; do 
    echo $e
  done
}

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arr1=(el1 el2 el3 el4)
arr2=(el5 el6 el7 el8)

printElems2 arr1[@]
printElems2 arr2[@]

More information about ‘indirect variable reference’ feature you can find here