mjhjmtu

Below is an example, where I am using two arrays which could be initiated with many elements, for now having "None" as the only element, is there any way to delete existing element/elements and then keep appending new elements when given condition matches otherwise leave the array unaltered.

Looking for a way with minimal coding.

array_a=(None)
array_b=(None)
declare -A DICT=([1]="source" [11]="destination" [2]="nowhere")
for index in $!DICT[@] ; do
 [[ $index =~ 1 ]] && array_a+=("$DICT[$index]") 
 [[ $index =~ 50 ]] && array_b+=("$DICT[$index]")
done 
echo $array_a[@]
echo $array_b[@]

Output:

None destination source 
None

Expected Output:

destination source
None

I am having a dumb solution for this

array_a=(None)
array_b=(None)
declare -A DICT=([1]="source" [11]="destination" [2]="nowhere")
a=0
b=0
for index in $!DICT[@] ; do
if [[ $index =~ 1 ]] ; then if [[ $a -eq 0 ]] ; then ((a++)) ; unset array_a ; fi ; array_a+=("$DICT[$index]") ; fi
if [[ $index =~ 50 ]]; then if [[ $b -eq 0 ]] ; then ((b++)) ; unset array_b ; fi ; array_b+=("$DICT[$index]") ; fi
done 
echo $array_a[@]
echo $array_b[@]

Output:

destination source
None

Use this:

ini_array_a=(None xyz)
ini_array_b=()
array_a=()
array_b=()
[...]
array_a=($array_a[@]:-$ini_array_a[@])
array_b=($array_b[@]:-$ini_array_b[@])
echo $array_a[@]:-None
echo $array_b[@]:-None

Where $ini_array_a and $ini_array_b are the already initialized arrays. We define two new arrays with no value inside. Then do your processing. For echoing the arrays, use Parameter Expansion. The arrays $array_a and array_b are those to print in the end (this is to address your comment).

$parameter:-word

 If parameter is unset or null, the expansion of word is substituted.
 Otherwise, the value of parameter is substituted.