How to rename an associative array in Bash?

Question

I need to loop over an associative array and drain the contents of it to a temp array (and perform some update to the value).

The leftover contents of the first array should then be discarded and i want to assign the temp array to the original array variable.

Sudo code:

declare -A MAINARRAY
declare -A TEMPARRAY
... populate ${MAINARRAY[...]} ...

while something; do     #Drain some values from MAINARRAY to TEMPARRAY
    ${TEMPARRAY["$name"]}=((${MAINARRAY["$name"]} + $somevalue))
done
... other manipulations to TEMPARRAY ...

unset MAINARRAY        #discard left over values that had no update
declare -A MAINARRAY
MAINARRAY=${TEMPARRAY[@]}  #assign updated TEMPARRAY back to MAINARRAY (ERROR HERE)

Answer 1

expanding on Luca Borrione's cp_hash - which didn't work for me, and I gave up trying to track down the eval expansion issue - I ran into differences before and after bash 4.2. after 4.2(something) this gets a lot easier... but that's not backwards compatible. See 1 and 2

so my variation tested on 4.1.2(1) and 4.3.46(1):

#!/bin/bash
## bash4 due to associative arrays!

    function cp_hash() {
        ## REQUIRES you to declare -A $2 in advance.
        local original_hash_name="$1"
        local copy_hash_name="$2"
        #
        # sadly we have no way to identify if you have already declared it, so bull ahead.
        #
        ## store the definition of the old array
        local __copy__=$(declare -p $original_hash_name)
        ## rename the array inside the definition
        __copy__=${__copy__/${original_hash_name}=/__copy__=}

        ## for bash 4.2 > we could end here.
        ## declare -A creates local scope variables by default, so add -g
        ## this DOES NOT work prior to 4.2, even w/o -g and w/ a declare outside.
        #    __copy__=${__copy__/${original_hash_name}=/${copy_hash_name}=}
        #    eval ${__copy__/-A/-g -A}

        ## for bash4 where we can't do -g, then:
        ## local associative array based on the definition we stored and modified
        eval ${__copy__}
        ## loop through the local copy, and store it in the declared-outside copy.
        for i in "${!__copy__[@]}"
        do
            eval ${copy_hash_name}[$i]=${__copy__[$i]}
        done
    }

    declare -A hash
    hash[hello]=world
    hash[ab]=cd

    #not required for 4.2+ if you use -g, neither helps nor hinders
    declare -A copy

    cp_hash 'hash' 'copy'

    echo hash: ${hash[@]}
    echo copy: ${copy[@]}

    echo "copy result loop"
    for i in "${!copy[@]}"
    do
        echo "key  : $i | value: ${copy[$i]}"
    done

Answer 2

MAINARRAY=( "${TEMPARRAY[@]}" )

Answer 3

Copying associative arrays is not directly possible in bash. The best solution probably is, as already been pointed out, to iterate through the array and copy it step by step.

There is another solution which I used to pass variables to functions. You could use the same technique for copying associative arrays:

# declare associative array
declare -A assoc_array=(["key1"]="value1" ["key2"]="value2")
# convert associative array to string
assoc_array_string=$(declare -p assoc_array)
# create new associative array from string
eval "declare -A new_assoc_array="${assoc_array_string#*=}
# show array definition
declare -p new_assoc_array

Answer 4

How about this one (Doesn't create a real copy, just a link to source variable):

#!/bin/bash
declare -A my_array=(["key1"]="value1" ["key2"]="value2")
declare -n arr=my_array
arr['LOG_FILE']=/tmp/log.txt
echo ${arr['key1']}
echo ${arr['LOG_FILE']}

Will print:

value1
/tmp/log.txt

Answer 5

With associative arrays, I don't believe there's any other method than iterating

for key in "${!TEMPARRAY[@]}"  # make sure you include the quotes there
do
  MAINARRAY["$key"]="${TEMPARRAY["$key"]}"
  # or: MAINARRAY+=( ["$key"]="${TEMPARRAY["$key"]}" )
done

Answer 6

Following both the suggestions of glenn jackman and ffeldhaus, you can build a function which might become handy:

function cp_hash
{
    local original_hash_name="$1"
    local copy_hash_name="$2"

    local __copy__=$(declare -p $original_hash_name);
    eval declare -A __copy__="${__copy__:$(expr index "${__copy__}" =)}";

    for i in "${!__copy__[@]}"
    do
        eval ${copy_hash_name}[$i]=${__copy__[$i]}
    done
}

Usage:

declare -A copy_hash_name
cp_hash 'original_hash_name' 'copy_hash_name'

Example:

declare -A hash
hash[hello]=world
hash[ab]=cd

declare -A copy
cp_hash 'hash' 'copy'

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

Will output

key  : ab | value: cd
key  : hello | value: world