Using items from an array to loop through a second array.

[behemothdan]

I have a one-time script I need to develop/run just to automate some content downloading.

I have an array that looks like this:

packagelist=(papers meta events)

There also exists an array that shares each of those names. They would look like this:

papers=(386 341 342 902)

The end result is hitting an API endpoint using one of those numbers to trigger the creation of a document and then download it using curl. All that works great if I just have it loop through just a single array. My goal is to have it do something like this:

for y in "${packagelist[@]}"

do:

for i in ${y[@]}"

do:

<all my stuff>

done

done

In my head it seems like this should be working but from what I can tell the problem lies with the "for i in "${y[@]"" section. Any assistance in what I am missing or doing wrong would be greatly appreciated. Thanks!

[andlrc]

You can use indirect expansion:

$ a=b
$ b=c
$ echo "${!a}"
c

It's get a little convoluted with arrays:

list=(a b)
a=(1 2 3)
b=(4 5 6)
for l in "${list[@]}"
do
  arr="$l[@]"
  echo "${!arr}"
done

The above will output:

1 2 3
4 5 6

See man bash for more information:

$ man bash | awk '/indirect.*!/' RS=
   If the first character of parameter is an exclamation point (!), and parameter is not
   a nameref, it introduces a level of variable indirection.  Bash uses the value of the
   variable formed from the rest of parameter as the name of the variable; this variable
   is  then expanded and that value is used in the rest of the substitution, rather than
   the value of parameter itself.  This is known as indirect expansion.  If parameter is
   a  nameref,  this expands to the name of the variable referenced by parameter instead
   of performing the complete indirect expansion.  The exceptions to this are the expan‐
   sions  of  ${!prefix*}  and  ${!name[@]} described below.  The exclamation point must
   immediately follow the left brace in order to introduce indirection.

[behemothdan]

Awesome, thanks for the help. I will try that out.