Defining an array from concatenated variables in bash

Question

Outside of the code I posted below I defined an array fanrp0[1] and fanrp0[2] I did the same for fans 0 through 3. I'm trying to make fstat change and echo each of the fans in two arrays.

    for (( f=1; f<=2; f++ ))
     do
       for (( f2=0; f2<=3; f2++ ))
        do
          fstat="${(fanrp$f2)[$f]}"
          echo $fstat
        done
     done

It looks like you're trying to do what bash refers to as an indirect reference, which are apparently fairly difficult and cumbersome to do with array variables, judging by this Bash FAQ page, which I found on this question. You can accomplish what you need with eval somewhat more easily, as in eval "fstat=\${fanrp$f2[$f]}", but keep in mind that there are some security issues with using eval. I'd start by reading that Bash FAQ page I linked to. — Mike Holt
– Mike Holt, Commented Mar 14, 2014 at 0:23
Indirect array references are easier once you start thinking of the [...] not as indexing syntax, but as part of the name of the variable. If you have an array foo, then foo[0], foo[1], etc. are just oddly named variables, each with their own value. Then x=foo[0] leads naturally to ${!x} being equivalent to ${foo[0]}. — chepner
– chepner, Commented Mar 14, 2014 at 2:51

chepner · Accepted Answer · 2014-03-14 02:56:11Z

3

If fanrp0, fanrp1, fanrp2, and fanrp3 are all arrays, you can write your loops as

for (( f=1; f<=2; f++ ))
do
  for (( f2=0; f2<=3; f2++ ))
  do
    x="fanrp$f2[$f]"
    fstat="${!x}"
    echo $fstat
  done
done

Since f2 is used only to generate the array names, a slightly cleaner syntax would be

for f in {1..2}; do
  for arr in fanrp{0..3}; do
    x="$arr[$f]"
    fstat=${!x}
    echo $fstat
  done
done

answered Mar 14, 2014 at 2:56

chepner

538k77 gold badges594 silver badges746 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Cfoote7 Over a year ago

The first option actually gave me a bad substitute error, that's what I wrote for my first attempt and I couldn't figure out why I was getting that error. However, I think your second solution made a lot more sense to me, thanks it worked great I wasn't aware of the for arr

Collectives™ on Stack Overflow

Defining an array from concatenated variables in bash

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related