Bash compose array with the input of other arrays, respecting a specific loop order

Question

I am trying to generate a new array, with the combination of other arrays, respecting a specific sequence. In pure Bash. Example:

numbers=(0 1 2 3 4 5 6 7 8); colors=(red blue green); loop_sequence=(numbers numbers colors numbers colors colors) 

Example output:

0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green... 

But I find very difficult to make the internal loops of iterations. Any help is very welcome.

Answer 1

Dynamic variable names are tricky in bash, but do-able with variable indirection.

numbers=(0 1 2 3 4 5 6 7 8) colors=(red blue green) loop_sequence=(numbers numbers colors numbers colors colors) # keep track of where you are in each array declare -A idx=([numbers]=0 [colors]=0) for varname in "${loop_sequence[@]}"; do tmp="${varname}[${idx[$varname]}]" # construct the array reference echo "$varname => ${!tmp}" # variable indirection gets the value (( idx[$varname]++ )) done 

outputs

numbers => 0 numbers => 1 colors => red numbers => 2 colors => blue colors => green 

To indefinitely repeat the loop_sequence, you can:

declare -A idx=([numbers]=0 [colors]=0) # store the array sizes for convenience declare -A size=([numbers]=${#numbers[@]} [colors]=${#colors[@]}) while true; do for varname in "${loop_sequence[@]}"; do tmp="${varname}[${idx[$varname]}]" echo "$varname => ${!tmp}" # loop the array index (( idx[$varname] = (idx[$varname]+1) % size[$varname] )) done done | less 

Answer 2

x=$(( (l=${#loop_sequence[@]}) * (n=${#numbers[@]}) * (c=${#colors[@]}))) _n= _c= _l= set -- math(){ return "$(($1-=-($1<${1#?})|$1-1))"; } while [ "$((x-=1))" -ge 0 ] do math _l case "${loop_sequence[$?-1]}" in n*) math _n set -- "$@" "${numbers[$?-1]}";; *) math _c set -- "$@" "${colors[$?-1]}";; esac done; printf %s\\n "$@" 

---

0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green 0 1 red 2 blue green 3 4 red 5 blue green 6 7 red 8 blue green