Bash – is there a way to list all ‘indexes IDs’ (keys) on a bash associative array variable

arraybash

I have this array:

declare -A astr

I add elements to it:

astr[elemA]=123
astr[elemB]=199

But later on I need to know what are the indexes IDs (elemA and elemB) and list them.

echo "${astr[@]}" #this only get me the values...

Best Answer

You can get the list of "keys" for the associative array like so:

$ echo "${!astr[@]}"
elemB elemA

You can iterate over the "keys" like so:

for i in "${!astr[@]}"
do   
  echo "key  : $i"
  echo "value: ${astr[$i]}"
done

Example

$ for i in "${!astr[@]}"; do echo "key  : $i"; echo "value: ${astr[$i]}"; done
key  : elemB
value: 199
key  : elemA
value: 123

References

How to iterate over associative array in bash

Related Solutions

Bash – How to sort an associative array and retain the keys

Assuming your keys don't contain colons or newlines and your values don't contain newlines:

for key in "${!MYARRAY[@]}"; do
  printf '%s:%s\n' "$key" "${MYARRAY[$key]}"
done | sort -t : -k 2n

If you need to arrange the key in the order given by the values, read back the output:

IFS=$'\n'; set -f
sorted_keys=($(
    for key in "${!MYARRAY[@]}"; do
      printf '%s:%s\n' "$key" "${MYARRAY[$key]}"
    done | sort -t : -k 2n | sed 's/:.*//'))
unset IFS; set +f

Bash Scripting – How to Read the Last Element of an Array

As of bash 4.2, you can just use a negative index ${myarray[-1]} to get the last element. You can do the same thing for the second-last, and so on; in Bash:

If the subscript used to reference an element of an indexed array evaluates to a number less than zero, it is interpreted as relative to one greater than the maximum index of the array, so negative indices count back from the end of the array, and an index of -1 refers to the last element.

The same also works for assignment. When it says "expression" it really means an expression; you can write in any arithmetic expression there to compute the index, including one that computes using the length of the array ${#myarray[@]} explicitly like ${myarray[${#myarray[@]} - 1]} for earlier versions.